阻尼滑动--能够滑动过度的ScrollView（OverScrollView）

贴上一个我自己用过的阻尼滑动的ScrollView，像QQ里面那种滑动效果，尽管不是我写的，可是我认为还能够，贴出来做个记录，实用到的时候免得到处去找。

代码例如以下：

/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import android.content.Context;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.FocusFinder;
import android.view.KeyEvent;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.view.animation.AnimationUtils;
import android.view.animation.OvershootInterpolator;
import android.widget.FrameLayout;
import android.widget.Scroller;
import android.view.View.OnTouchListener;

import java.lang.reflect.Field;
import java.util.List;

/**
 * Layout container for a view hierarchy that can be scrolled by the user,
 * allowing it to be larger than the physical display. A ScrollView is a
 * {@link FrameLayout}, meaning you should place one child in it containing the
 * entire contents to scroll; this child may itself be a layout manager with a
 * complex hierarchy of objects. A child that is often used is a
 * {@link LinearLayout} in a vertical orientation, presenting a vertical array
 * of top-level items that the user can scroll through.
 *
 * <p>
 * The {@link TextView} class also takes care of its own scrolling, so does not
 * require a ScrollView, but using the two together is possible to achieve the
 * effect of a text view within a larger container.
 *
 * <p>
 * ScrollView only supports vertical scrolling.
 */
public class OverScrollView extends FrameLayout implements OnTouchListener
{
	private static final String TAG = OverScrollView.class.getName();
	static final int ANIMATED_SCROLL_GAP = 250;

	static final float MAX_SCROLL_FACTOR = 0.5f;
	private static final float SCROLL_RATIO = 0.3f;// 阻尼系数
	static final float OVERSHOOT_TENSION = 0.75f;

	private long mLastScroll;

	private final Rect mTempRect = new Rect();
	private Scroller mScroller;

	protected Context mContext;

	Field mScrollYField;
	Field mScrollXField;

	boolean hasFailedObtainingScrollFields;
	int prevScrollY;
	boolean isInFlingMode = false;

	DisplayMetrics metrics;
	LayoutInflater inflater;
	protected View child;

	private Runnable overScrollerSpringbackTask;

	/**
	 * Flag to indicate that we are moving focus ourselves. This is so the code
	 * that watches for focus changes initiated outside this ScrollView knows
	 * that it does not have to do anything.
	 */
	private boolean mScrollViewMovedFocus;

	/**
	 * Position of the last motion event.
	 */
	private float mLastMotionY;

	/**
	 * True when the layout has changed but the traversal has not come through
	 * yet. Ideally the view hierarchy would keep track of this for us.
	 */
	private boolean mIsLayoutDirty = true;

	/**
	 * The child to give focus to in the event that a child has requested focus
	 * while the layout is dirty. This prevents the scroll from being wrong if
	 * the child has not been laid out before requesting focus.
	 */
	private View mChildToScrollTo = null;

	/**
	 * True if the user is currently dragging this ScrollView around. This is
	 * not the same as 'is being flinged', which can be checked by
	 * mScroller.isFinished() (flinging begins when the user lifts his finger).
	 */
	private boolean mIsBeingDragged = false;

	/**
	 * Determines speed during touch scrolling
	 */
	private VelocityTracker mVelocityTracker;

	/**
	 * When set to true, the scroll view measure its child to make it fill the
	 * currently visible area.
	 */
	private boolean mFillViewport;

	/**
	 * Whether arrow scrolling is animated.
	 */
	private boolean mSmoothScrollingEnabled = true;

	private int mTouchSlop;
	private int mMinimumVelocity;
	private int mMaximumVelocity;

	/**
	 * ID of the active pointer. This is used to retain consistency during
	 * drags/flings if multiple pointers are used.
	 */
	private int mActivePointerId = INVALID_POINTER;

	/**
	 * Sentinel value for no current active pointer. Used by
	 * {@link #mActivePointerId}.
	 */
	private static final int INVALID_POINTER = -1;

	public OverScrollView(Context context)
	{
		this(context, null);
		mContext = context;
		initBounce();
	}

	public OverScrollView(Context context, AttributeSet attrs)
	{

		this(context, attrs, 0);
		mContext = context;
		initBounce();
	}

	public OverScrollView(Context context, AttributeSet attrs, int defStyle)
	{
		super(context, attrs, defStyle);
		mContext = context;

		initScrollView();
		setFillViewport(true);
		initBounce();
	}

	private void initBounce()
	{
		metrics = this.mContext.getResources().getDisplayMetrics();

		// init the bouncy scroller, and make sure the layout is being drawn
		// after the top padding
		mScroller = new Scroller(getContext(), new OvershootInterpolator(OVERSHOOT_TENSION));
		overScrollerSpringbackTask = new Runnable()
		{
			@Override
			public void run()
			{
				// scroll till after the padding
				mScroller.computeScrollOffset();
				scrollTo(0, mScroller.getCurrY());

				if (!mScroller.isFinished())
				{
					post(this);
				}
			}
		};
		prevScrollY = getPaddingTop();

		try
		{
			mScrollXField = View.class.getDeclaredField("mScrollX");
			mScrollYField = View.class.getDeclaredField("mScrollY");

		} catch (Exception e)
		{
			hasFailedObtainingScrollFields = true;
		}
	}

	private void SetScrollY(int value)
	{
		if (mScrollYField != null)
		{
			try
			{
				mScrollYField.setInt(this, value);
			} catch (Exception e)
			{
			}
		}
	}

	private void SetScrollX(int value)
	{
		if (mScrollXField != null)
		{
			try
			{
				mScrollXField.setInt(this, value);
			} catch (Exception e)
			{
			}
		}
	}

	public void initChildPointer()
	{
		Log.i(TAG,"initChildPointer");
		child = getChildAt(0);
		child.setPadding(0, 1500, 0, 1500);

	}

	@Override
	protected float getTopFadingEdgeStrength()
	{
		if (getChildCount() == 0)
		{
			return 0.0f;
		}

		final int length = getVerticalFadingEdgeLength();
		if (getScrollY() < length)
		{
			return getScrollY() / (float) length;
		}

		return 1.0f;
	}

	@Override
	protected float getBottomFadingEdgeStrength()
	{
		if (getChildCount() == 0)
		{
			return 0.0f;
		}

		final int length = getVerticalFadingEdgeLength();
		final int bottomEdge = getHeight() - getPaddingBottom();
		final int span = getChildAt(0).getBottom() - getScrollY() - bottomEdge;
		if (span < length)
		{
			return span / (float) length;
		}

		return 1.0f;
	}

	/**
	 * @return The maximum amount this scroll view will scroll in response to an
	 *         arrow event.
	 */
	public int getMaxScrollAmount()
	{
		return (int) (MAX_SCROLL_FACTOR * (getBottom() - getTop()));
	}

	private void initScrollView()
	{
		mScroller = new Scroller(getContext());
		setFocusable(true);
		setDescendantFocusability(FOCUS_AFTER_DESCENDANTS);
		setWillNotDraw(false);
		final ViewConfiguration configuration = ViewConfiguration.get(mContext);
		mTouchSlop = configuration.getScaledTouchSlop();
		mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
		mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();

		setOnTouchListener(this);

		post(new Runnable()
		{
			public void run()
			{
				scrollTo(0, child.getPaddingTop());
			}
		});
	}

	@Override
	public void addView(View child)
	{
		if (getChildCount() > 0)
		{
			throw new IllegalStateException("ScrollView can host only one direct child");
		}

		super.addView(child);
		initChildPointer();
	}

	@Override
	public void addView(View child, int index)
	{
		if (getChildCount() > 0)
		{
			throw new IllegalStateException("ScrollView can host only one direct child");
		}

		super.addView(child, index);
		initChildPointer();
	}

	@Override
	public void addView(View child, ViewGroup.LayoutParams params)
	{
		if (getChildCount() > 0)
		{
			throw new IllegalStateException("ScrollView can host only one direct child");
		}

		super.addView(child, params);
		initChildPointer();
	}

	@Override
	public void addView(View child, int index, ViewGroup.LayoutParams params)
	{
		if (getChildCount() > 0)
		{
			throw new IllegalStateException("ScrollView can host only one direct child");
		}

		super.addView(child, index, params);
	}

	/**
	 * @return Returns true this ScrollView can be scrolled
	 */
	private boolean canScroll()
	{
		View child = getChildAt(0);
		if (child != null)
		{
			int childHeight = child.getHeight();
			return getHeight() < childHeight + getPaddingTop() + getPaddingBottom();
		}
		return false;
	}

	/**
	 * Indicates whether this ScrollView's content is stretched to fill the
	 * viewport.
	 *
	 * @return True if the content fills the viewport, false otherwise.
	 */
	public boolean isFillViewport()
	{
		return mFillViewport;
	}

	/**
	 * Indicates this ScrollView whether it should stretch its content height to
	 * fill the viewport or not.
	 *
	 * @param fillViewport
	 *            True to stretch the content's height to the viewport's
	 *            boundaries, false otherwise.
	 */
	public void setFillViewport(boolean fillViewport)
	{
		if (fillViewport != mFillViewport)
		{
			mFillViewport = fillViewport;
			requestLayout();
		}
	}

	/**
	 * @return Whether arrow scrolling will animate its transition.
	 */
	public boolean isSmoothScrollingEnabled()
	{
		return mSmoothScrollingEnabled;
	}

	/**
	 * Set whether arrow scrolling will animate its transition.
	 *
	 * @param smoothScrollingEnabled
	 *            whether arrow scrolling will animate its transition
	 */
	public void setSmoothScrollingEnabled(boolean smoothScrollingEnabled)
	{
		mSmoothScrollingEnabled = smoothScrollingEnabled;
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
	{
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);

		if (!mFillViewport)
		{
			return;
		}

		final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
		if (heightMode == MeasureSpec.UNSPECIFIED)
		{
			return;
		}

		if (getChildCount() > 0)
		{
			final View child = getChildAt(0);
			int height = getMeasuredHeight();
			if (child.getMeasuredHeight() < height)
			{
				final FrameLayout.LayoutParams lp = (LayoutParams) child.getLayoutParams();

				int childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec, getPaddingLeft() + getPaddingRight(), lp.width);
				height -= getPaddingTop();
				height -= getPaddingBottom();
				int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);

				child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
			}
		}
	}

	@Override
	public boolean dispatchKeyEvent(KeyEvent event)
	{
		// Let the focused view and/or our descendants get the key first
		return super.dispatchKeyEvent(event) || executeKeyEvent(event);
	}

	/**
	 * You can call this function yourself to have the scroll view perform
	 * scrolling from a key event, just as if the event had been dispatched to
	 * it by the view hierarchy.
	 *
	 * @param event
	 *            The key event to execute.
	 * @return Return true if the event was handled, else false.
	 */
	public boolean executeKeyEvent(KeyEvent event)
	{
		mTempRect.setEmpty();

		if (!canScroll())
		{
			if (isFocused() && event.getKeyCode() != KeyEvent.KEYCODE_BACK)
			{
				View currentFocused = findFocus();
				if (currentFocused == this)
					currentFocused = null;
				View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused, View.FOCUS_DOWN);
				return nextFocused != null && nextFocused != this && nextFocused.requestFocus(View.FOCUS_DOWN);
			}
			return false;
		}

		boolean handled = false;
		if (event.getAction() == KeyEvent.ACTION_DOWN)
		{
			switch (event.getKeyCode())
			{
			case KeyEvent.KEYCODE_DPAD_UP:
				if (!event.isAltPressed())
				{
					handled = arrowScroll(View.FOCUS_UP);
				} else
				{
					handled = fullScroll(View.FOCUS_UP);
				}
				break;
			case KeyEvent.KEYCODE_DPAD_DOWN:
				if (!event.isAltPressed())
				{
					handled = arrowScroll(View.FOCUS_DOWN);
				} else
				{
					handled = fullScroll(View.FOCUS_DOWN);
				}
				break;
			case KeyEvent.KEYCODE_SPACE:
				pageScroll(event.isShiftPressed() ?

View.FOCUS_UP : View.FOCUS_DOWN);
				break;
			}
		}

		return handled;
	}

	public boolean inChild(int x, int y)
	{
		if (getChildCount() > 0)
		{
			final int scrollY = getScrollY();
			final View child = getChildAt(0);
			return !(y < child.getTop() - scrollY || y >= child.getBottom() - scrollY || x < child.getLeft() || x >= child.getRight());
		}
		return false;
	}

	@Override
	public boolean onInterceptTouchEvent(MotionEvent ev)
	{
		/*
		 * This method JUST determines whether we want to intercept the motion.
		 * If we return true, onMotionEvent will be called and we do the actual
		 * scrolling there.
		 */

		/*
		 * Shortcut the most recurring case: the user is in the dragging state
		 * and he is moving his finger. We want to intercept this motion.
		 */
		final int action = ev.getAction();
		if ((action == MotionEvent.ACTION_MOVE) && (mIsBeingDragged))
		{
			return true;
		}

		switch (action & MotionEvent.ACTION_MASK)
		{
		case MotionEvent.ACTION_MOVE:
		{
			/*
			 * mIsBeingDragged == false, otherwise the shortcut would have
			 * caught it. Check whether the user has moved far enough from his
			 * original down touch.
			 */

			/*
			 * Locally do absolute value. mLastMotionY is set to the y value of
			 * the down event.
			 */
			final int activePointerId = mActivePointerId;
			if (activePointerId == INVALID_POINTER)
			{
				// If we don't have a valid id, the touch down wasn't on
				// content.
				break;
			}

			final int pointerIndex = ev.findPointerIndex(activePointerId);
			final float y = ev.getY(pointerIndex);
			final int yDiff = (int) Math.abs(y - mLastMotionY);
			if (yDiff > mTouchSlop)
			{
				mIsBeingDragged = true;
				mLastMotionY = y;
			}
			break;
		}

		case MotionEvent.ACTION_DOWN:
		{
			final float y = ev.getY();
			if (!inChild((int) ev.getX(), (int) y))
			{
				mIsBeingDragged = false;
				break;
			}

			/*
			 * Remember location of down touch. ACTION_DOWN always refers to
			 * pointer index 0.
			 */
			mLastMotionY = y;
			mActivePointerId = ev.getPointerId(0);

			/*
			 * If being flinged and user touches the screen, initiate drag;
			 * otherwise don't. mScroller.isFinished should be false when being
			 * flinged.
			 */
			mIsBeingDragged = !mScroller.isFinished();
			break;
		}

		case MotionEvent.ACTION_CANCEL:
		case MotionEvent.ACTION_UP:
			/* Release the drag */
			mIsBeingDragged = false;
			mActivePointerId = INVALID_POINTER;
			break;
		case MotionEvent.ACTION_POINTER_UP:
			onSecondaryPointerUp(ev);
			break;
		}

		/*
		 * The only time we want to intercept motion events is if we are in the
		 * drag mode.
		 */
		return mIsBeingDragged;
	}

	@Override
	public boolean onTouchEvent(MotionEvent ev)
	{

		if (ev.getAction() == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0)
		{
			// Don't handle edge touches immediately -- they may actually belong
			// to one of our
			// descendants.
			return false;
		}

		if (mVelocityTracker == null)
		{
			mVelocityTracker = VelocityTracker.obtain();
		}
		mVelocityTracker.addMovement(ev);

		final int action = ev.getAction();

		switch (action & MotionEvent.ACTION_MASK)
		{
		case MotionEvent.ACTION_DOWN:
		{
			final float y = ev.getY();
			if (!(mIsBeingDragged = inChild((int) ev.getX(), (int) y)))
			{
				return false;
			}

			/*
			 * If being flinged and user touches, stop the fling. isFinished
			 * will be false if being flinged.
			 */
			if (!mScroller.isFinished())
			{
				mScroller.abortAnimation();
			}

			// Remember where the motion event started
			mLastMotionY = y;
			mActivePointerId = ev.getPointerId(0);
			break;
		}
		case MotionEvent.ACTION_MOVE:
			if (mIsBeingDragged)
			{
				// Scroll to follow the motion event
				final int activePointerIndex = ev.findPointerIndex(mActivePointerId);
				final float y = ev.getY(activePointerIndex);
				final int deltaY = (int) (mLastMotionY - y);
				mLastMotionY = y;

				if (isOverScrolled())
				{
					// when overscrolling, move the scroller just half of the
					// finger movement, to make it feel like a spring...
					scrollBy(0,(int)(deltaY * SCROLL_RATIO));
				} else
				{
					scrollBy(0, deltaY);
				}
			}
			break;
		case MotionEvent.ACTION_UP:
			if (mIsBeingDragged)
			{
				final VelocityTracker velocityTracker = mVelocityTracker;
				velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
				int initialVelocity = (int) velocityTracker.getYVelocity(mActivePointerId);

				if (getChildCount() > 0 && Math.abs(initialVelocity) > mMinimumVelocity)
				{
					fling(-initialVelocity);
				}

				mActivePointerId = INVALID_POINTER;
				mIsBeingDragged = false;

				if (mVelocityTracker != null)
				{
					mVelocityTracker.recycle();
					mVelocityTracker = null;
				}
			}
			break;
		case MotionEvent.ACTION_CANCEL:
			if (mIsBeingDragged && getChildCount() > 0)
			{
				mActivePointerId = INVALID_POINTER;
				mIsBeingDragged = false;
				if (mVelocityTracker != null)
				{
					mVelocityTracker.recycle();
					mVelocityTracker = null;
				}
			}
			break;
		case MotionEvent.ACTION_POINTER_UP:
			onSecondaryPointerUp(ev);
			break;
		}
		return true;
	}

	public boolean isOverScrolled()
	{
		return (getScrollY() < child.getPaddingTop() || getScrollY() > child.getBottom() - child.getPaddingBottom() - getHeight());
	}

	private void onSecondaryPointerUp(MotionEvent ev)
	{
		final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
		final int pointerId = ev.getPointerId(pointerIndex);
		if (pointerId == mActivePointerId)
		{
			// This was our active pointer going up. Choose a new
			// active pointer and adjust accordingly.
			// TODO: Make this decision more intelligent.
			final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
			mLastMotionY = ev.getY(newPointerIndex);
			mActivePointerId = ev.getPointerId(newPointerIndex);
			if (mVelocityTracker != null)
			{
				mVelocityTracker.clear();
			}
		}
	}

	/**
	 * <p>
	 * Finds the next focusable component that fits in this View's bounds
	 * (excluding fading edges) pretending that this View's top is located at
	 * the parameter top.
	 * </p>
	 *
	 * @param topFocus
	 *            look for a candidate is the one at the top of the bounds if
	 *            topFocus is true, or at the bottom of the bounds if topFocus
	 *            is false
	 * @param top
	 *            the top offset of the bounds in which a focusable must be
	 *            found (the fading edge is assumed to start at this position)
	 * @param preferredFocusable
	 *            the View that has highest priority and will be returned if it
	 *            is within my bounds (null is valid)
	 * @return the next focusable component in the bounds or null if none can be
	 *         found
	 */
	private View findFocusableViewInMyBounds(final boolean topFocus, final int top, View preferredFocusable)
	{
		/*
		 * The fading edge's transparent side should be considered for focus
		 * since it's mostly visible, so we divide the actual fading edge length
		 * by 2.
		 */
		final int fadingEdgeLength = getVerticalFadingEdgeLength() / 2;
		final int topWithoutFadingEdge = top + fadingEdgeLength;
		final int bottomWithoutFadingEdge = top + getHeight() - fadingEdgeLength;

		if ((preferredFocusable != null) && (preferredFocusable.getTop() < bottomWithoutFadingEdge)
				&& (preferredFocusable.getBottom() > topWithoutFadingEdge))
		{
			return preferredFocusable;
		}

		return findFocusableViewInBounds(topFocus, topWithoutFadingEdge, bottomWithoutFadingEdge);
	}

	/**
	 * <p>
	 * Finds the next focusable component that fits in the specified bounds.
	 * </p>
	 *
	 * @param topFocus
	 *            look for a candidate is the one at the top of the bounds if
	 *            topFocus is true, or at the bottom of the bounds if topFocus
	 *            is false
	 * @param top
	 *            the top offset of the bounds in which a focusable must be
	 *            found
	 * @param bottom
	 *            the bottom offset of the bounds in which a focusable must be
	 *            found
	 * @return the next focusable component in the bounds or null if none can be
	 *         found
	 */
	private View findFocusableViewInBounds(boolean topFocus, int top, int bottom)
	{

		List<View> focusables = getFocusables(View.FOCUS_FORWARD);
		View focusCandidate = null;

		/*
		 * A fully contained focusable is one where its top is below the bound's
		 * top, and its bottom is above the bound's bottom. A partially
		 * contained focusable is one where some part of it is within the
		 * bounds, but it also has some part that is not within bounds. A fully
		 * contained focusable is preferred to a partially contained focusable.
		 */
		boolean foundFullyContainedFocusable = false;

		int count = focusables.size();
		for (int i = 0; i < count; i++)
		{
			View view = focusables.get(i);
			int viewTop = view.getTop();
			int viewBottom = view.getBottom();

			if (top < viewBottom && viewTop < bottom)
			{
				/*
				 * the focusable is in the target area, it is a candidate for
				 * focusing
				 */

				final boolean viewIsFullyContained = (top < viewTop) && (viewBottom < bottom);

				if (focusCandidate == null)
				{
					/* No candidate, take this one */
					focusCandidate = view;
					foundFullyContainedFocusable = viewIsFullyContained;
				} else
				{
					final boolean viewIsCloserToBoundary = (topFocus && viewTop < focusCandidate.getTop())
							|| (!topFocus && viewBottom > focusCandidate.getBottom());

					if (foundFullyContainedFocusable)
					{
						if (viewIsFullyContained && viewIsCloserToBoundary)
						{
							/*
							 * We're dealing with only fully contained views, so
							 * it has to be closer to the boundary to beat our
							 * candidate
							 */
							focusCandidate = view;
						}
					} else
					{
						if (viewIsFullyContained)
						{
							/*
							 * Any fully contained view beats a partially
							 * contained view
							 */
							focusCandidate = view;
							foundFullyContainedFocusable = true;
						} else if (viewIsCloserToBoundary)
						{
							/*
							 * Partially contained view beats another partially
							 * contained view if it's closer
							 */
							focusCandidate = view;
						}
					}
				}
			}
		}

		return focusCandidate;
	}

	/**
	 * <p>
	 * Handles scrolling in response to a "page up/down" shortcut press. This
	 * method will scroll the view by one page up or down and give the focus to
	 * the topmost/bottommost component in the new visible area. If no component
	 * is a good candidate for focus, this scrollview reclaims the focus.
	 * </p>
	 *
	 * @param direction
	 *            the scroll direction: {@link android.view.View#FOCUS_UP} to go
	 *            one page up or {@link android.view.View#FOCUS_DOWN} to go one
	 *            page down
	 * @return true if the key event is consumed by this method, false otherwise
	 */
	public boolean pageScroll(int direction)
	{
		boolean down = direction == View.FOCUS_DOWN;
		int height = getHeight();

		if (down)
		{
			mTempRect.top = getScrollY() + height;
			int count = getChildCount();
			if (count > 0)
			{
				View view = getChildAt(count - 1);
				if (mTempRect.top + height > view.getBottom())
				{
					mTempRect.top = view.getBottom() - height;
				}
			}
		} else
		{
			mTempRect.top = getScrollY() - height;
			if (mTempRect.top < 0)
			{
				mTempRect.top = 0;
			}
		}
		mTempRect.bottom = mTempRect.top + height;

		return scrollAndFocus(direction, mTempRect.top, mTempRect.bottom);
	}

	/**
	 * <p>
	 * Handles scrolling in response to a "home/end" shortcut press. This method
	 * will scroll the view to the top or bottom and give the focus to the
	 * topmost/bottommost component in the new visible area. If no component is
	 * a good candidate for focus, this scrollview reclaims the focus.
	 * </p>
	 *
	 * @param direction
	 *            the scroll direction: {@link android.view.View#FOCUS_UP} to go
	 *            the top of the view or {@link android.view.View#FOCUS_DOWN} to
	 *            go the bottom
	 * @return true if the key event is consumed by this method, false otherwise
	 */
	public boolean fullScroll(int direction)
	{
		boolean down = direction == View.FOCUS_DOWN;
		int height = getHeight();

		mTempRect.top = 0;
		mTempRect.bottom = height;

		if (down)
		{
			int count = getChildCount();
			if (count > 0)
			{
				View view = getChildAt(count - 1);
				mTempRect.bottom = view.getBottom();
				mTempRect.top = mTempRect.bottom - height;
			}
		}

		return scrollAndFocus(direction, mTempRect.top, mTempRect.bottom);
	}

	/**
	 * <p>
	 * Scrolls the view to make the area defined by <code>top</code> and
	 * <code>bottom</code> visible. This method attempts to give the focus to a
	 * component visible in this area. If no component can be focused in the new
	 * visible area, the focus is reclaimed by this scrollview.
	 * </p>
	 *
	 * @param direction
	 *            the scroll direction: {@link android.view.View#FOCUS_UP} to go
	 *            upward {@link android.view.View#FOCUS_DOWN} to downward
	 * @param top
	 *            the top offset of the new area to be made visible
	 * @param bottom
	 *            the bottom offset of the new area to be made visible
	 * @return true if the key event is consumed by this method, false otherwise
	 */
	private boolean scrollAndFocus(int direction, int top, int bottom)
	{
		boolean handled = true;

		int height = getHeight();
		int containerTop = getScrollY();
		int containerBottom = containerTop + height;
		boolean up = direction == View.FOCUS_UP;

		View newFocused = findFocusableViewInBounds(up, top, bottom);
		if (newFocused == null)
		{
			newFocused = this;
		}

		if (top >= containerTop && bottom <= containerBottom)
		{
			handled = false;
		} else
		{
			int delta = up ?

(top - containerTop) : (bottom - containerBottom);
			doScrollY(delta);
		}

		if (newFocused != findFocus() && newFocused.requestFocus(direction))
		{
			mScrollViewMovedFocus = true;
			mScrollViewMovedFocus = false;
		}

		return handled;
	}

	/**
	 * Handle scrolling in response to an up or down arrow click.
	 *
	 * @param direction
	 *            The direction corresponding to the arrow key that was pressed
	 * @return True if we consumed the event, false otherwise
	 */
	public boolean arrowScroll(int direction)
	{

		View currentFocused = findFocus();
		if (currentFocused == this)
			currentFocused = null;

		View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused, direction);

		final int maxJump = getMaxScrollAmount();

		if (nextFocused != null && isWithinDeltaOfScreen(nextFocused, maxJump, getHeight()))
		{
			nextFocused.getDrawingRect(mTempRect);
			offsetDescendantRectToMyCoords(nextFocused, mTempRect);
			int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
			doScrollY(scrollDelta);
			nextFocused.requestFocus(direction);
		} else
		{
			// no new focus
			int scrollDelta = maxJump;

			if (direction == View.FOCUS_UP && getScrollY() < scrollDelta)
			{
				scrollDelta = getScrollY();
			} else if (direction == View.FOCUS_DOWN)
			{
				if (getChildCount() > 0)
				{
					int daBottom = getChildAt(0).getBottom();

					int screenBottom = getScrollY() + getHeight();

					if (daBottom - screenBottom < maxJump)
					{
						scrollDelta = daBottom - screenBottom;
					}
				}
			}
			if (scrollDelta == 0)
			{
				return false;
			}
			doScrollY(direction == View.FOCUS_DOWN ?

scrollDelta : -scrollDelta);
		}

		if (currentFocused != null && currentFocused.isFocused() && isOffScreen(currentFocused))
		{
			// previously focused item still has focus and is off screen, give
			// it up (take it back to ourselves)
			// (also, need to temporarily force FOCUS_BEFORE_DESCENDANTS so we
			// are
			// sure to
			// get it)
			final int descendantFocusability = getDescendantFocusability(); // save
			setDescendantFocusability(ViewGroup.FOCUS_BEFORE_DESCENDANTS);
			requestFocus();
			setDescendantFocusability(descendantFocusability); // restore
		}
		return true;
	}

	/**
	 * @return whether the descendant of this scroll view is scrolled off
	 *         screen.
	 */
	private boolean isOffScreen(View descendant)
	{
		return !isWithinDeltaOfScreen(descendant, 0, getHeight());
	}

	/**
	 * @return whether the descendant of this scroll view is within delta pixels
	 *         of being on the screen.
	 */
	private boolean isWithinDeltaOfScreen(View descendant, int delta, int height)
	{
		descendant.getDrawingRect(mTempRect);
		offsetDescendantRectToMyCoords(descendant, mTempRect);

		return (mTempRect.bottom + delta) >= getScrollY() && (mTempRect.top - delta) <= (getScrollY() + height);
	}

	/**
	 * Smooth scroll by a Y delta
	 *
	 * @param delta
	 *            the number of pixels to scroll by on the Y axis
	 */
	private void doScrollY(int delta)
	{
		if (delta != 0)
		{
			if (mSmoothScrollingEnabled)
			{
				smoothScrollBy(0, delta);
			} else
			{
				scrollBy(0, delta);
			}
		}
	}

	/**
	 * Like {@link View#scrollBy}, but scroll smoothly instead of immediately.
	 *
	 * @param dx
	 *            the number of pixels to scroll by on the X axis
	 * @param dy
	 *            the number of pixels to scroll by on the Y axis
	 */
	public final void smoothScrollBy(int dx, int dy)
	{
		if (getChildCount() == 0)
		{
			// Nothing to do.
			return;
		}
		long duration = AnimationUtils.currentAnimationTimeMillis() - mLastScroll;
		if (duration > ANIMATED_SCROLL_GAP)
		{
			final int height = getHeight() - getPaddingBottom() - getPaddingTop();
			final int bottom = getChildAt(0).getHeight();
			final int maxY = Math.max(0, bottom - height);
			final int scrollY = getScrollY();
			dy = Math.max(0, Math.min(scrollY + dy, maxY)) - scrollY;

			mScroller.startScroll(getScrollX(), scrollY, 0, dy);
			invalidate();
		} else
		{
			if (!mScroller.isFinished())
			{
				mScroller.abortAnimation();
			}
			scrollBy(dx, dy);
		}
		mLastScroll = AnimationUtils.currentAnimationTimeMillis();
	}

	public final void smoothScrollToTop()
	{
		smoothScrollTo(0, child.getPaddingTop());
	}

	public final void smoothScrollToBottom()
	{
		smoothScrollTo(0, child.getHeight() - child.getPaddingTop() - getHeight());
	}

	/**
	 * Like {@link #scrollTo}, but scroll smoothly instead of immediately.
	 *
	 * @param x
	 *            the position where to scroll on the X axis
	 * @param y
	 *            the position where to scroll on the Y axis
	 */
	public final void smoothScrollTo(int x, int y)
	{
		smoothScrollBy(x - getScrollX(), y - getScrollY());
	}

	/**
	 * <p>
	 * The scroll range of a scroll view is the overall height of all of its
	 * children.
	 * </p>
	 */
	@Override
	protected int computeVerticalScrollRange()
	{
		final int count = getChildCount();
		final int contentHeight = getHeight() - getPaddingBottom() - getPaddingTop();
		if (count == 0)
		{
			return contentHeight;
		}

		return getChildAt(0).getBottom();
	}

	@Override
	protected int computeVerticalScrollOffset()
	{
		return Math.max(0, super.computeVerticalScrollOffset());
	}

	@Override
	protected void measureChild(View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec)
	{
		ViewGroup.LayoutParams lp = child.getLayoutParams();

		int childWidthMeasureSpec;
		int childHeightMeasureSpec;

		childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec, getPaddingLeft() + getPaddingRight(), lp.width);

		childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);

		child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
	}

	@Override
	protected void measureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec,
			int heightUsed)
	{
		final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

		final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec, getPaddingLeft() + getPaddingRight() + lp.leftMargin
				+ lp.rightMargin + widthUsed, lp.width);
		final int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(lp.topMargin + lp.bottomMargin, MeasureSpec.UNSPECIFIED);

		child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
	}

	@Override
	public void computeScroll()
	{
		// If android implementation has changed and we cannot obtain mScrollY -
		// The default behavior will be applied by the parent.
		if (hasFailedObtainingScrollFields)
		{
			super.computeScroll();
			return;
		}

		if (mScroller.computeScrollOffset())
		{
			// This is called at drawing time by ViewGroup. We don't want to
			// re-show the scrollbars at this point, which scrollTo will do,
			// so we replicate most of scrollTo here.
			//
			// It's a little odd to call onScrollChanged from inside the
			// drawing.
			//
			// It is, except when you remember that computeScroll() is used to
			// animate scrolling. So unless we want to defer the
			// onScrollChanged()
			// until the end of the animated scrolling, we don't really have a
			// choice here.
			//
			// I agree. The alternative, which I think would be worse, is to
			// post
			// something and tell the subclasses later. This is bad because
			// there
			// will be a window where getScrollX()/Y is different from what the
			// app
			// thinks it is.
			//
			int oldX = getScrollX();
			int oldY = getScrollY();
			int x = mScroller.getCurrX();
			int y = mScroller.getCurrY();

			if (getChildCount() > 0)
			{
				View child = getChildAt(0);
				x = clamp(x, getWidth() - getPaddingRight() - getPaddingLeft(), child.getWidth());
				y = clamp(y, getHeight() - getPaddingBottom() - getPaddingTop(), child.getHeight());
				if (x != oldX || y != oldY)
				{
					SetScrollX(x);
					// mScrollX = x;
					SetScrollY(y);
					// mScrollY = y;
					onScrollChanged(x, y, oldX, oldY);
				}
			}
			awakenScrollBars();

			// Keep on drawing until the animation has finished.
			postInvalidate();
		}
	}

	/**
	 * Scrolls the view to the given child.
	 *
	 * @param child
	 *            the View to scroll to
	 */
	private void scrollToChild(View child)
	{
		child.getDrawingRect(mTempRect);

		/* Offset from child's local coordinates to ScrollView coordinates */
		offsetDescendantRectToMyCoords(child, mTempRect);

		int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);

		if (scrollDelta != 0)
		{
			scrollBy(0, scrollDelta);
		}
	}

	/**
	 * If rect is off screen, scroll just enough to get it (or at least the
	 * first screen size chunk of it) on screen.
	 *
	 * @param rect
	 *            The rectangle.
	 * @param immediate
	 *            True to scroll immediately without animation
	 * @return true if scrolling was performed
	 */
	private boolean scrollToChildRect(Rect rect, boolean immediate)
	{
		final int delta = computeScrollDeltaToGetChildRectOnScreen(rect);
		final boolean scroll = delta != 0;
		if (scroll)
		{
			if (immediate)
			{
				scrollBy(0, delta);
			} else
			{
				smoothScrollBy(0, delta);
			}
		}
		return scroll;
	}

	/**
	 * Compute the amount to scroll in the Y direction in order to get a
	 * rectangle completely on the screen (or, if taller than the screen, at
	 * least the first screen size chunk of it).
	 *
	 * @param rect
	 *            The rect.
	 * @return The scroll delta.
	 */
	protected int computeScrollDeltaToGetChildRectOnScreen(Rect rect)
	{
		if (getChildCount() == 0)
			return 0;

		int height = getHeight();
		int screenTop = getScrollY();
		int screenBottom = screenTop + height;

		int fadingEdge = getVerticalFadingEdgeLength();

		// leave room for top fading edge as long as rect isn't at very top
		if (rect.top > 0)
		{
			screenTop += fadingEdge;
		}

		// leave room for bottom fading edge as long as rect isn't at very
		// bottom
		if (rect.bottom < getChildAt(0).getHeight())
		{
			screenBottom -= fadingEdge;
		}

		int scrollYDelta = 0;

		if (rect.bottom > screenBottom && rect.top > screenTop)
		{
			// need to move down to get it in view: move down just enough so
			// that the entire rectangle is in view (or at least the first
			// screen size chunk).

			if (rect.height() > height)
			{
				// just enough to get screen size chunk on
				scrollYDelta += (rect.top - screenTop);
			} else
			{
				// get entire rect at bottom of screen
				scrollYDelta += (rect.bottom - screenBottom);
			}

			// make sure we aren't scrolling beyond the end of our content
			int bottom = getChildAt(0).getBottom();
			int distanceToBottom = bottom - screenBottom;
			scrollYDelta = Math.min(scrollYDelta, distanceToBottom);

		} else if (rect.top < screenTop && rect.bottom < screenBottom)
		{
			// need to move up to get it in view: move up just enough so that
			// entire rectangle is in view (or at least the first screen
			// size chunk of it).

			if (rect.height() > height)
			{
				// screen size chunk
				scrollYDelta -= (screenBottom - rect.bottom);
			} else
			{
				// entire rect at top
				scrollYDelta -= (screenTop - rect.top);
			}

			// make sure we aren't scrolling any further than the top our
			// content
			scrollYDelta = Math.max(scrollYDelta, -getScrollY());
		}
		return scrollYDelta;
	}

	@Override
	public void requestChildFocus(View child, View focused)
	{
		if (!mScrollViewMovedFocus)
		{
			if (!mIsLayoutDirty)
			{
				scrollToChild(focused);
			} else
			{
				// The child may not be laid out yet, we can't compute the
				// scroll yet
				mChildToScrollTo = focused;
			}
		}
		super.requestChildFocus(child, focused);
	}

	/**
	 * When looking for focus in children of a scroll view, need to be a little
	 * more careful not to give focus to something that is scrolled off screen.
	 *
	 * This is more expensive than the default {@link android.view.ViewGroup}
	 * implementation, otherwise this behavior might have been made the default.
	 */
	@Override
	protected boolean onRequestFocusInDescendants(int direction, Rect previouslyFocusedRect)
	{

		// convert from forward / backward notation to up / down / left / right
		// (ugh).
		if (direction == View.FOCUS_FORWARD)
		{
			direction = View.FOCUS_DOWN;
		} else if (direction == View.FOCUS_BACKWARD)
		{
			direction = View.FOCUS_UP;
		}

		final View nextFocus = previouslyFocusedRect == null ? FocusFinder.getInstance().findNextFocus(this, null, direction) : FocusFinder
				.getInstance().findNextFocusFromRect(this, previouslyFocusedRect, direction);

		if (nextFocus == null)
		{
			return false;
		}

		if (isOffScreen(nextFocus))
		{
			return false;
		}

		return nextFocus.requestFocus(direction, previouslyFocusedRect);
	}

	@Override
	public boolean requestChildRectangleOnScreen(View child, Rect rectangle, boolean immediate)
	{
		// offset into coordinate space of this scroll view
		rectangle.offset(child.getLeft() - child.getScrollX(), child.getTop() - child.getScrollY());

		return scrollToChildRect(rectangle, immediate);
	}

	@Override
	public void requestLayout()
	{
		mIsLayoutDirty = true;
		super.requestLayout();
	}

	@Override
	protected void onLayout(boolean changed, int l, int t, int r, int b)
	{
		super.onLayout(changed, l, t, r, b);
		mIsLayoutDirty = false;
		// Give a child focus if it needs it
		if (mChildToScrollTo != null && isViewDescendantOf(mChildToScrollTo, this))
		{
			scrollToChild(mChildToScrollTo);
		}
		mChildToScrollTo = null;

		// Calling this with the present values causes it to re-clam them
		scrollTo(getScrollX(), getScrollY());
		post(new Runnable()
		{
			public void run()
			{
				scrollTo(0, child.getPaddingTop());
			}
		});
	}

	@Override
	protected void onSizeChanged(int w, int h, int oldw, int oldh)
	{
		super.onSizeChanged(w, h, oldw, oldh);

		View currentFocused = findFocus();
		if (null == currentFocused || this == currentFocused)
			return;

		// If the currently-focused view was visible on the screen when the
		// screen was at the old height, then scroll the screen to make that
		// view visible with the new screen height.
		if (isWithinDeltaOfScreen(currentFocused, 0, oldh))
		{
			currentFocused.getDrawingRect(mTempRect);
			offsetDescendantRectToMyCoords(currentFocused, mTempRect);
			int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
			doScrollY(scrollDelta);
		}
	}

	@Override
	protected void onScrollChanged(int leftOfVisibleView, int topOfVisibleView, int oldLeftOfVisibleView, int oldTopOfVisibleView)
	{
		int displayHeight = getHeight();
		int paddingTop = child.getPaddingTop();
		int contentBottom = child.getHeight() - child.getPaddingBottom();

		if (isInFlingMode)
		{

			if (topOfVisibleView < paddingTop || topOfVisibleView > contentBottom - displayHeight)
			{
				if (topOfVisibleView < paddingTop)
				{
					mScroller.startScroll(0, topOfVisibleView, 0, paddingTop - topOfVisibleView, 1000);
				} else if (topOfVisibleView > contentBottom - displayHeight)
				{
					mScroller.startScroll(0, topOfVisibleView, 0, contentBottom - displayHeight - topOfVisibleView, 1000);
				}

				// Start animation.
				post(overScrollerSpringbackTask);
				isInFlingMode = false;
				return;

			}
		}
		super.onScrollChanged(leftOfVisibleView, topOfVisibleView, oldLeftOfVisibleView, oldTopOfVisibleView);
	}

	/**
	 * Return true if child is an descendant of parent, (or equal to the
	 * parent).
	 */
	private boolean isViewDescendantOf(View child, View parent)
	{
		if (child == parent)
		{
			return true;
		}

		final ViewParent theParent = child.getParent();
		return (theParent instanceof ViewGroup) && isViewDescendantOf((View) theParent, parent);
	}

	/**
	 * Fling the scroll view
	 *
	 * @param velocityY
	 *            The initial velocity in the Y direction. Positive numbers mean
	 *            that the finger/cursor is moving down the screen, which means
	 *            we want to scroll towards the top.
	 */
	public void fling(int velocityY)
	{
		if (getChildCount() > 0)
		{
			int height = getHeight() - getPaddingBottom() - getPaddingTop();
			int bottom = getChildAt(0).getHeight();

			mScroller.fling(getScrollX(), getScrollY(), 0, velocityY, 0, 0, 0, Math.max(0, bottom - height));

			final boolean movingDown = velocityY > 0;

			View newFocused = findFocusableViewInMyBounds(movingDown, mScroller.getFinalY(), findFocus());
			if (newFocused == null)
			{
				newFocused = this;
			}

			if (newFocused != findFocus() && newFocused.requestFocus(movingDown ? View.FOCUS_DOWN : View.FOCUS_UP))
			{
				mScrollViewMovedFocus = true;
				mScrollViewMovedFocus = false;
			}

			invalidate();
		}
	}

	/**
	 * {@inheritDoc}
	 *
	 * <p>
	 * This version also clamps the scrolling to the bounds of our child.
	 */
	@Override
	public void scrollTo(int x, int y)
	{
		// we rely on the fact the View.scrollBy calls scrollTo.
		if (getChildCount() > 0)
		{
			View child = getChildAt(0);
			x = clamp(x, getWidth() - getPaddingRight() - getPaddingLeft(), child.getWidth());
			y = clamp(y, getHeight() - getPaddingBottom() - getPaddingTop(), child.getHeight());
			if (x != getScrollX() || y != getScrollY())
			{
				super.scrollTo(x, y);
			}
		}
	}

	private int clamp(int n, int my, int child)
	{
		if (my >= child || n < 0)
		{
			/*
			 * my >= child is this case: |--------------- me ---------------|
			 * |------ child ------| or |--------------- me ---------------|
			 * |------ child ------| or |--------------- me ---------------|
			 * |------ child ------|
			 *
			 * n < 0 is this case: |------ me ------| |-------- child --------|
			 * |-- getScrollX() --|
			 */
			return 0;
		}
		if ((my + n) > child)
		{
			/*
			 * this case: |------ me ------| |------ child ------| |--
			 * getScrollX() --|
			 */
			return child - my;
		}
		return n;
	}

	@Override
	public boolean onTouch(View v, MotionEvent event)
	{
		// Stop scrolling calculation.
		mScroller.forceFinished(true);
		// Stop scrolling animation.
		removeCallbacks(overScrollerSpringbackTask);

		if (event.getAction() == MotionEvent.ACTION_UP)
		{
			return overScrollView();
		}

		else if (event.getAction() == MotionEvent.ACTION_CANCEL)
		{
			return overScrollView();
		}

		return false;
	}

	private boolean overScrollView()
	{

		// The height of scroll view, in pixels
		int displayHeight = getHeight();
		Log.i(TAG , "displayHeight = "+displayHeight);
		// The top of content view, in pixels.
		int contentTop = child.getPaddingTop();
		// The top of content view, in pixels.
		int contentBottom = child.getHeight() - child.getPaddingBottom();
		// The scrolled top position of scroll view, in pixels.
		int currScrollY = getScrollY();
		Log.i(TAG , "currScrollY = "+currScrollY);
		Log.i(TAG , "contentTop = "+contentTop);
		int scrollBy;

		// Scroll to content top
		if (currScrollY < contentTop)
		{

			onOverScroll(currScrollY);
			scrollBy = contentTop - currScrollY;
		} else if (currScrollY + displayHeight > contentBottom)
		{
			// Scroll to content top
			if (child.getHeight() - child.getPaddingTop() - child.getPaddingBottom() < displayHeight)
			{

				scrollBy = contentTop - currScrollY;
			}
			// Scroll to content bottom
			else
			{

				scrollBy = contentBottom - displayHeight - currScrollY;
				// Log.d(Definitions.LOG_TAG, "scrollBy=" + scrollBy);
			}

			// fire onOverScroll event, and update scrollBy if a loadingView has
			// been added to the scroller.
			scrollBy += onOverScroll(currScrollY);
		}
		// scrolling between the contentTop and contentBottom
		else
		{
			isInFlingMode = true;
			return false;
		}
		mScroller.startScroll(0, currScrollY, 0, scrollBy, 500);

		// Start animation.
		post(overScrollerSpringbackTask);

		prevScrollY = currScrollY;

		// consume(to stop fling)
		return true;

	}

	protected int onOverScroll(int scrollY)
	{
		return 0;
	}

}

拿去能够直接用哟