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

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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 bit13             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 position22             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     @Override26     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {27         super.onMeasure(widthMeasureSpec, heightMeasureSpec);28     }29 30     @Override31     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 textview34         //add 100px for right35         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.

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