android中getWidth()和getMeasuredWidth()之间的区别

先给出一个结论：getMeasuredWidth()获取的是view原始的大小，也就是这个view在XML文件中配置或者是代码中设置的大小。getWidth（）获取的是这个view最终显示的大小，这个大小有可能等于原始的大小也有可能不等于原始大小。

从源码上开始分析一下这两个方法的区别。首先来看一下getMeasuredWidth()这个方法。

   public final int getMeasuredWidth() {
         return mMeasuredWidth & MEASURED_SIZE_MASK;
     }
 
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
         setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
                 getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
     }
 
   protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) {
         boolean optical = isLayoutModeOptical(this);
         if (optical != isLayoutModeOptical(mParent)) {
             Insets insets = getOpticalInsets();
             int opticalWidth  = insets.left + insets.right;
             int opticalHeight = insets.top  + insets.bottom;
 
             measuredWidth  += optical ? opticalWidth  : -opticalWidth;
             measuredHeight += optical ? opticalHeight : -opticalHeight;
         }
         setMeasuredDimensionRaw(measuredWidth, measuredHeight);
     }
 
   private void setMeasuredDimensionRaw(int measuredWidth, int measuredHeight) {
         mMeasuredWidth = measuredWidth;
25         mMeasuredHeight = measuredHeight;
 
         mPrivateFlags |= PFLAG_MEASURED_DIMENSION_SET;
     }

从源码上来看，getMeasuredWidth（）获取的是mMeasuredWidth的这个值。这个值是一个8位的十六进制的数字，高两位表示的是这个measure阶段的Mode的值，具体可以查看MeasureSpec的原理。这里mMeasuredWidth & MEASURED_SIZE_MASK表示的是测量阶段结束之后，view真实的值。而且这个值会在调用了setMeasuredDimensionRaw（）函数之后会被设置。所以getMeasuredWidth（）的值是measure阶段结束之后得到的view的原始的值。

再来看看getWidth（）的源码：

   public final int getWidth() {
         return mRight - mLeft;
     }

那么问题来了，mRight和mLeft是什么值，是在什么时候被设置的。我们再看layout阶段的源码：

   public void layout(int l, int t, int r, int b) {
         if ((mPrivateFlags3 & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) {
             onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec);
             mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
         }
 
         int oldL = mLeft;
         int oldT = mTop;
         int oldB = mBottom;
         int oldR = mRight;
 
         boolean changed = isLayoutModeOptical(mParent) ?
                 setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);
 
       ...
 }

在layout阶段会去调用setOpticalFrame（）或者调用setFrame（）方法，从源码中可知setOpticalFrame（）方法，最终还是调用的setFrame（）方法。

   protected boolean setFrame(int left, int top, int right, int bottom) {
         boolean changed = false;
 
         if (DBG) {
             Log.d("View", this + " View.setFrame(" + left + "," + top + ","
                     + right + "," + bottom + ")");
         }
 
         if (mLeft != left || mRight != right || mTop != top || mBottom != bottom) {
             changed = true;
 
             // Remember our drawn bit
             int drawn = mPrivateFlags & PFLAG_DRAWN;
 
             int oldWidth = mRight - mLeft;
             int oldHeight = mBottom - mTop;
             int newWidth = right - left;
             int newHeight = bottom - top;
             boolean sizeChanged = (newWidth != oldWidth) || (newHeight != oldHeight);
 
             // Invalidate our old position
             invalidate(sizeChanged);
 
             mLeft = left;
             mTop = top;
             mRight = right;
             mBottom = bottom;
             mRenderNode.setLeftTopRightBottom(mLeft, mTop, mRight, mBottom);
 
             mPrivateFlags |= PFLAG_HAS_BOUNDS;
    ...
 }

所以最终的mLeft和mRight的值是在setFrame（）方法中被设置的。而且这些mLeft，mRight代表了view最终显示在界面中的大小。

下面我们自定义一个简单的ViewGroup，在layout阶段改变left，right的值，观察getMeasuredWidth（）和getWidth（）方法之间的区别。

 package com.gearmotion.app.customviewgroup;
 
 import android.content.Context;
 import android.util.AttributeSet;
 import android.view.View;
 import android.widget.RelativeLayout;
 
 /**
  * Created by Charles on 2015/11/21.
  */
 public class CustomViewGroup extends RelativeLayout {
 
     public CustomViewGroup(Context context) {
         super(context);
     }
 
     public CustomViewGroup(Context context, AttributeSet attrs) {
         super(context, attrs);
     }
 
     public CustomViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {
         super(context, attrs, defStyleAttr);
     }
 
     @Override
     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
         super.onMeasure(widthMeasureSpec, heightMeasureSpec);
     }
 
     @Override
     protected void onLayout(boolean changed, int l, int t, int r, int b) {
         super.onLayout(changed, l, t, r, b);
         View child = this.getChildAt(1);  //the textview
         //add 100px for right
         child.layout(child.getLeft(), child.getTop(),child.getRight() + 100,child.getBottom());
 
     }

<?xml version="1.0" encoding="utf-8"?>
<com.gearmotion.app.customviewgroup.CustomViewGroup xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.gearmotion.app.customviewgroup.MainActivity">
 
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
 
        <Button
            android:id="@+id/left"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center"
            android:text="width" />
 
        <Button
            android:id="@+id/right"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center"
            android:text="measuredWidth" />
    </LinearLayout>
 
    <TextView
        android:id="@+id/textview"
        android:layout_width="100px"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:background="#8EE5EE"
        android:gravity="center"
        android:text="textview" />
 
</com.gearmotion.app.customviewgroup.CustomViewGroup>

package com.gearmotion.app.customviewgroup;
 
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
 
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
 
    TextView mTextView;
    Button mLeftBtn;
    Button mRightBtn;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        mTextView = (TextView) this.findViewById(R.id.textview);
        mLeftBtn = (Button) this.findViewById(R.id.left);
        mRightBtn = (Button) this.findViewById(R.id.right);
        mLeftBtn.setOnClickListener(this);
        mRightBtn.setOnClickListener(this);
    }
 
    @Override
    public void onClick(View v) {
        int id = v.getId();
        switch (id) {
            case R.id.left:   //width
                Toast.makeText(MainActivity.this, "width:" + mTextView.getWidth(), Toast.LENGTH_SHORT).show();
                break;
            case R.id.right:  //measuredWidth
                Toast.makeText(MainActivity.this,"measuredWidth:"+mTextView.getMeasuredWidth(),Toast.LENGTH_SHORT).show();
                break;
        }
    }
}

在这个demo中，我们给textview设置宽度为100px，但是在layout阶段给它加大到200，最终结果是：点击width按钮，显示为200，点解measuredWidth按钮显示为100.