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。

1   public final int getMeasuredWidth() {
2         return mMeasuredWidth & MEASURED_SIZE_MASK;
3     }
4
5   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
6         setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
7                 getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
8     }
9
10   protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) {
11         boolean optical = isLayoutModeOptical(this);
12         if (optical != isLayoutModeOptical(mParent)) {
13             Insets insets = getOpticalInsets();
14             int opticalWidth  = insets.left + insets.right;
15             int opticalHeight = insets.top  + insets.bottom;
16
17             measuredWidth  += optical ? opticalWidth  : -opticalWidth;
18             measuredHeight += optical ? opticalHeight : -opticalHeight;
19         }
20         setMeasuredDimensionRaw(measuredWidth, measuredHeight);
21     }
22
23   private void setMeasuredDimensionRaw(int measuredWidth, int measuredHeight) {
24         mMeasuredWidth = measuredWidth;
25         mMeasuredHeight = measuredHeight;
26
27         mPrivateFlags |= PFLAG_MEASURED_DIMENSION_SET;
28     }

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：

1   public final int getWidth() {
2         return mRight - mLeft;
3     }

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：

1   public void layout(int l, int t, int r, int b) {
2         if ((mPrivateFlags3 & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) {
3             onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec);
4             mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
5         }
6
7         int oldL = mLeft;
8         int oldT = mTop;
9         int oldB = mBottom;
10         int oldR = mRight;
11
12         boolean changed = isLayoutModeOptical(mParent) ?
13                 setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);
14
15       ...
16 }

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。

1   protected boolean setFrame(int left, int top, int right, int bottom) {
2         boolean changed = false;
3
4         if (DBG) {
5             Log.d("View", this + " View.setFrame(" + left + "," + top + ","
6                     + right + "," + bottom + ")");
7         }
8
9         if (mLeft != left || mRight != right || mTop != top || mBottom != bottom) {
10             changed = true;
11
12             // Remember our drawn bit
13             int drawn = mPrivateFlags & PFLAG_DRAWN;
14
15             int oldWidth = mRight - mLeft;
16             int oldHeight = mBottom - mTop;
17             int newWidth = right - left;
18             int newHeight = bottom - top;
19             boolean sizeChanged = (newWidth != oldWidth) || (newHeight != oldHeight);
20
21             // Invalidate our old position
22             invalidate(sizeChanged);
23
24             mLeft = left;
25             mTop = top;
26             mRight = right;
27             mBottom = bottom;
28             mRenderNode.setLeftTopRightBottom(mLeft, mTop, mRight, mBottom);
29
30             mPrivateFlags |= PFLAG_HAS_BOUNDS;
31    ...
32 }

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。

1 package com.gearmotion.app.customviewgroup;
2
3 import android.content.Context;
4 import android.util.AttributeSet;
5 import android.view.View;
6 import android.widget.RelativeLayout;
7
8 /**
9  * Created by Charles on 2015/11/21.
10  */
11 public class CustomViewGroup extends RelativeLayout {
12
13     public CustomViewGroup(Context context) {
14         super(context);
15     }
16
17     public CustomViewGroup(Context context, AttributeSet attrs) {
18         super(context, attrs);
19     }
20
21     public CustomViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {
22         super(context, attrs, defStyleAttr);
23     }
24
25     @Override
26     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
27         super.onMeasure(widthMeasureSpec, heightMeasureSpec);
28     }
29
30     @Override
31     protected void onLayout(boolean changed, int l, int t, int r, int b) {
32         super.onLayout(changed, l, t, r, b);
33         View child = this.getChildAt(1);  //the textview
34         //add 100px for right
35         child.layout(child.getLeft(), child.getTop(),child.getRight() + 100,child.getBottom());
36
37
38     }
39

<?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.