ViewFlow增强onItemClick功能及ViewFlow AbsListView源代码分析

先看实现效果，上图： 

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ViewFlow是一个非常好用的，用于不确定item个数的水平滑动切换的开源项目。

可是从github上下载的ViewFlow事实上是不支持onItemClick功能的，touch事件中并没有处理click。 

那么怎样去支持onItemClick功能呢？

一、在实现前，先带着三个问题:

序号	问题
1	ViewFlow须要OnItemClickListener接口吗?
2	ListView又是怎样实现OnItemClick的呢?
3	OnItemClick又是怎样被调用的呢?

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1.1、问题一

从源代码中能够看出ViewFlow是继承extends AdapterView 的。而AdapterView就是通常ListView、GridView等继承的且已经定义过OnItemClickListener了。

1.2、问题二

分析ListView源代码知道其继承extends AbsListView。而AbsListView又是继承extends AdapterView。

在AbsListView中事实上是实现了OnItemClickListener了。那么接下来的步骤仅仅要变化，仿AbsListView实现OnItemClick就可以。

1.3、问题三

分析AbsListView源代码。能够发现有个方法performItemClick方法。此方法一运行，自然就运行到了OnItemClick，不多说上源代码看：

/**
     * Call the OnItemClickListener, if it is defined.
     *
     * @param view The view within the AdapterView that was clicked.
     * @param position The position of the view in the adapter.
     * @param id The row id of the item that was clicked.
     * @return True if there was an assigned OnItemClickListener that was
     *         called, false otherwise is returned.
     */
    public boolean performItemClick(View view, int position, long id) {
        if (mOnItemClickListener != null) {
            playSoundEffect(SoundEffectConstants.CLICK);
            if (view != null) {
                view.sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
            }
            mOnItemClickListener.onItemClick(this, view, position, id);
            return true;
        }

        return false;
    }

那么仅仅要我们想办法在ViewFlow中运行performItemClick就OK了。

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二、AbsListView是怎样运行performItemClick?

一般用onItemClick中比較重要的是方法入參的postion。那么怎样获取postion呢?

2.1、postion的获取

2.1.1 在AbsListView的onTouchEvent中，在MotionEvent.ACTION_DOWN时evnet.getX与event.getY，获取出x与y坐标，再依据pointToPosition方法计算出点击item的position下标。截取片断代码例如以下：

@Override
    public boolean onTouchEvent(MotionEvent ev) {
        if (!isEnabled()) {
            // A disabled view that is clickable still consumes the touch
            // events, it just doesn't respond to them.
            return isClickable() || isLongClickable();
        }
        ....
        switch (action & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN: {
            switch (mTouchMode) {
            case TOUCH_MODE_OVERFLING: {
                ...
                break;
            }

            default: {
                mActivePointerId = ev.getPointerId(0);
                final int x = (int) ev.getX();
                final int y = (int) ev.getY();
                int motionPosition = pointToPosition(x, y);//计算出down的是哪个item的postion
	}

2.1.2 pointToPosition方法例如以下：

/**
     * Maps a point to a position in the list.
     *
     * @param x X in local coordinate
     * @param y Y in local coordinate
     * @return The position of the item which contains the specified point, or
     *         {@link #INVALID_POSITION} if the point does not intersect an item.
     */
    public int pointToPosition(int x, int y) {
        Rect frame = mTouchFrame;
        if (frame == null) {//仅仅是为了避免反复new Rect
            mTouchFrame = new Rect();
            frame = mTouchFrame;
        }

        final int count = getChildCount();
        for (int i = count - 1; i >= 0; i--) {
            final View child = getChildAt(i);
            if (child.getVisibility() == View.VISIBLE) {
                child.getHitRect(frame);//获取子控件在父控件坐标系中的矩形坐标
                if (frame.contains(x, y)) {
                    return mFirstPosition + i;
                }
            }
        }
        return INVALID_POSITION;
    }

2.2、PerformClick的运行

2.2.1 点击也是在touch里处理的。那么直接看onTouchEvent中怎样将点击关联运行的。

  case MotionEvent.ACTION_UP: {
            switch (mTouchMode) {
            case TOUCH_MODE_DOWN:
            case TOUCH_MODE_TAP:
            case TOUCH_MODE_DONE_WAITING:
                final int motionPosition = mMotionPosition;
                final View child = getChildAt(motionPosition - mFirstPosition);

                ....
                //构造了PerformClick内部来用于运行点击事件
	             if (mPerformClick == null) {
                       mPerformClick = new PerformClick();
	              }
                    final AbsListView.PerformClick performClick = mPerformClick;
                    performClick.mClickMotionPosition = motionPosition;
                    performClick.rememberWindowAttachCount();
....

   if (mTouchMode == TOUCH_MODE_DOWN || mTouchMode == TOUCH_MODE_TAP) {
   ...
    mLayoutMode = LAYOUT_NORMAL;
    if (!mDataChanged && mAdapter.isEnabled(motionPosition)) {
       ....
        if (mTouchModeReset != null) {
            removeCallbacks(mTouchModeReset);
        }
        mTouchModeReset = new Runnable() {
            @Override
            public void run() {
                mTouchMode = TOUCH_MODE_REST;
                child.setPressed(false);
                setPressed(false);
                if (!mDataChanged) {
                    performClick.run();//直接运行run方法
                }
            }
        };
        postDelayed(mTouchModeReset,
                ViewConfiguration.getPressedStateDuration());
    	} else {
       	 mTouchMode = TOUCH_MODE_REST;
        	updateSelectorState();
    	}
    	return true;
	} else if (!mDataChanged && mAdapter.isEnabled(motionPosition)) {
    	performClick.run();//直接运行run方法
	...

2.2.2 再看看PerformClick是怎样实现的

/**
     * A base class for Runnables that will check that their view is still attached to
     * the original window as when the Runnable was created.
     *
     */
    private class WindowRunnnable { //只用于推断当前即将要运行click时window是否是同一窗体，有没有由于异常情况新开的窗体了
        private int mOriginalAttachCount;

        public void rememberWindowAttachCount() {
            mOriginalAttachCount = getWindowAttachCount();
        }

        public boolean sameWindow() {
            return hasWindowFocus() && getWindowAttachCount() == mOriginalAttachCount;
        }
    }

    private class PerformClick extends WindowRunnnable implements Runnable {
        int mClickMotionPosition;

        public void run() {
            // The data has changed since we posted this action in the event queue,
            // bail out before bad things happen
            if (mDataChanged) return;

            final ListAdapter adapter = mAdapter;
            final int motionPosition = mClickMotionPosition;
            if (adapter != null && mItemCount > 0 &&
                    motionPosition != INVALID_POSITION &&
                    motionPosition < adapter.getCount() && sameWindow()) {
                final View view = getChildAt(motionPosition - mFirstPosition);
                // If there is no view, something bad happened (the view scrolled off the
                // screen, etc.) and we should cancel the click
                if (view != null) {//performItemClick被运行，至此AbsListView实现了onItemClick了
                    performItemClick(view, motionPosition, adapter.getItemId(motionPosition));
                }
            }
        }
    }

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三、ViewFlow运行performItemClick?

3.1、postion的获取

ViewFlow的postion事实上和AbsListView的postion获取有点差别。由于ViewFlow是水平滑动而AbsListView是竖向的。

item会不在同一屏幕宽中。使用x与y坐标再遍历ChildView的矩形坐标系并不能适用。

那么怎样来获取postion呢?

翻看源代码有ViewFlow有个ViewSwitchListener，onSwitched中有对应的postion与View。

仅仅须要查看onSwitched在何处被调用，postion与view是怎样被斌值就可以。

private void postViewSwitched(int direction) {
		if (direction == 0)
			return;

		if (direction > 0) { // to the right
			mCurrentAdapterIndex++;
			mCurrentBufferIndex++;
			...

		} else { // to the left
			mCurrentAdapterIndex--;
			mCurrentBufferIndex--;
			...
		}

		...
		if (mViewSwitchListener != null) { //通过在构造方法mLoadedViews(List<View>)初始化,mCurrentAdapterIndex当前显示的adapter中position位置
			mViewSwitchListener
					.onSwitched(mLoadedViews.get(mCurrentBufferIndex),
							mCurrentAdapterIndex);
		}
		logBuffer();
	}

3.2、PerformClick的运行

同AbsListView的PerformClick运行是同理，这里也是通过在0nTouchEvent的up中运行的。

@Override
	public boolean onTouchEvent(MotionEvent ev) {
		....

		final int action = ev.getAction();
		final float x = ev.getX();

		//---------add start  获取Y坐标
		final float y = ev.getY();
		//---------add end

		switch (action) {
		case MotionEvent.ACTION_DOWN:
			...

			// Remember where the motion event started
			mLastMotionX = x;
			//---------add start
			mLastMotionY = y;
			//---------add start
			mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST
					: TOUCH_STATE_SCROLLING;
			mIsClick = true; //每次down是默认是一次点击事件，在move中有x轴或y轴的偏移时则取消是click
			break;

		case MotionEvent.ACTION_MOVE:
			final int deltaX = (int) (mLastMotionX - x);

			boolean xMoved = Math.abs(deltaX) > mTouchSlop;
			//---------add start  计算y移动偏移量 推断y轴是否有移动过及本次down下，是否是一次click事件
			float tempDeltaX = mLastMotionX - ev.getX();
			float tempdeltaY = mLastMotionY - ev.getY();
			boolean isXMoved = Math.abs(tempDeltaX) > MOVE_TOUCHSLOP;
			boolean isYMoved = Math.abs(tempdeltaY) > MOVE_TOUCHSLOP;
			boolean tempIsMoved = isXMoved || isYMoved ; //xy有点偏移都觉得不是点击事件
			mIsClick = !tempIsMoved;  //若x与y偏移量都过小，则觉得是一次click事件
			//Log.e("------->", "ACTION_MOVE tempDeltaX:"+tempDeltaX+" tempdeltaY: "+tempdeltaY+" mTouchSlop:"+mTouchSlop+" isXMoved:"+isXMoved+" isYMoved:"+isYMoved+" isClick:"+mIsClick);
			//---------add start  

			...
			break;

		case MotionEvent.ACTION_UP:
			....
			//------------------若是一次click。则运行点击。

这里仿AbsListView 採用PerformClick
			//Log.e("------->", "ACTION_UP isClick:"+mIsClick);
			if(mIsClick){
				if (mPerformClick == null) {
					mPerformClick = new PerformClick();
				}
				final ViewFlow.PerformClick performClick = mPerformClick;
				performClick.mClickMotionPosition = mCurrentAdapterIndex;
				performClick.rememberWindowAttachCount(); //记录点击时的连接窗体次数
				performClick.run();
			}
			//------------------
			.....

			break;
		....
		}
		return true;
	}

而PerformClick的实现例如以下：

/**
     * A base class for Runnables that will check that their view is still attached to
     * the original window as when the Runnable was created.
     *
     */
    private class WindowRunnnable {
        private int mOriginalAttachCount;

        public void rememberWindowAttachCount() {
            mOriginalAttachCount = getWindowAttachCount(); //getWindowAttachCount 获取控件绑在窗体上的次数
        }

        public boolean sameWindow() {  //推断是否是同一个窗体，异常情况时界面attachWindowCount会是+1，那么此时就不是同一个窗体了。
            return hasWindowFocus() && getWindowAttachCount() == mOriginalAttachCount;
        }
    }

    private class PerformClick extends WindowRunnnable implements Runnable {
        int mClickMotionPosition;

        public void run() {
            // The data has changed since we posted this action in the event queue,
            // bail out before bad things happen
            //if (mDataChanged) return;

            final Adapter adapter = mAdapter;
            final int motionPosition = mClickMotionPosition;
			if (adapter != null && mAdapter.getCount() > 0 &&
                    motionPosition != INVALID_POSITION &&
                    motionPosition < adapter.getCount() && sameWindow()) {
                //final View view = getChildAt(motionPosition - mFirstPosition); // mFirstPosition不关注
                final View view = mLoadedViews.get(mCurrentBufferIndex); //position及view的获取借鉴onSwitched方法
                // If there is no view, something bad happened (the view scrolled off the
                // screen, etc.) and we should cancel the click
                if (view != null) {
                    performItemClick(view, motionPosition, adapter.getItemId(motionPosition));
                }
            }
        }
    }

至此搞定了ViewFlow的onItemClick了。

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附

最后上个ViewFlow的使用演示样例Demo

public class CircleViewFlowExample extends Activity {

	private ViewFlow viewFlow;

	/** Called when the activity is first created. */
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setTitle(R.string.circle_title);
		setContentView(R.layout.circle_layout);

		viewFlow = (ViewFlow) findViewById(R.id.viewflow);
		viewFlow.setOnItemClickListener(new OnItemClickListener() {

			@Override
			public void onItemClick(AdapterView<?

> parent, View view,
					int position, long id) {
				Toast.makeText(CircleViewFlowExample.this, "CircleViewFlowExample点击了position:"+position+"的图片", 1).show();
				Log.e("-----", "CircleViewFlowExample点击了position:"+position+"的图片");
			}
		});
		viewFlow.setAdapter(new ImageAdapter(this), 5);
		CircleFlowIndicator indic = (CircleFlowIndicator) findViewById(R.id.viewflowindic);
		viewFlow.setFlowIndicator(indic);
		Log.e("-----", "CircleViewFlowExample onCreate");
	}
	/* If your min SDK version is < 8 you need to trigger the onConfigurationChanged in ViewFlow manually, like this */
	@Override
	public void onConfigurationChanged(Configuration newConfig) {
		super.onConfigurationChanged(newConfig);
		viewFlow.onConfigurationChanged(newConfig);
	}
}

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总结

先吐槽一两句：CSDN的markdown编辑的时候感觉好爽，但最后保存公布时。老是出问题。

不是timeout，就是服务异常，公布不了。

保存在草稿箱中也能够正常预览。就是不能正常公布。

无奈仅仅好转成普通模式。代码都一块一块贴进来。郁闷....

github上ViewFlow下载地址：

https://github.com/pakerfeldt/android-viewflow

完整源代码demo下载(支持onItemClick的ViewFlow)

http://download.csdn.net/detail/chenshufei2/9003119