前言

前几天被问到了getMeasuredWidth和getWidth之间的区别，因此回来看了一下源码，又顺便复习了一遍measure/layout/draw的过程，有兴趣的同学可以看前面的几篇文章

• View 绘制体系知识梳理(3) - 绘制流程之 Measure 详解
• View 绘制体系知识梳理(4) - 绘制过程之 Layout 详解
• View 绘制体系知识梳理(5) - 绘制过程之 Draw 详解

一、getMeasuredWidth 和 getWidth 的定义

1.1 getMeasuredWidth

我们来看一下getMeasuredWidth方法的内部实现：

    /*** Like {@link #getMeasuredWidthAndState()}, but only returns the* raw width component (that is the result is masked by* {@link #MEASURED_SIZE_MASK}).** @return The raw measured width of this view.*/public final int getMeasuredWidth() {return mMeasuredWidth & MEASURED_SIZE_MASK;}
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这里可以看到，该方法返回的是setMeasuredDimensionRaw中设置的mMeasuredWidth的size部分，也就是说，该方法返回的是在 测量阶段中计算出的宽度。

    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;mMeasuredHeight = measuredHeight;}
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1.2 getWidth

    /*** Return the width of the your view.** @return The width of your view, in pixels.*/@ViewDebug.ExportedProperty(category = "layout")public final int getWidth() {return mRight - mLeft;}
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getWidth的值是根据mRight和mLeft之间的差值计算出来的，在setFrame方法中，会对View的四个点坐标mLeft/mRigth/mTop/mBottom进行赋值，它决定了View在其父容器中所处的位置：

    protected boolean setFrame(int left, int top, int right, int bottom) {boolean changed = false;if (mLeft != left || mRight != right || mTop != top || mBottom != bottom) {changed = true;mLeft = left;mTop = top;mRight = right;mBottom = bottom;//....}return changed;}
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而setFrame就是在layout过程中调用的：

    public void layout(int l, int t, int r, int b) {int oldL = mLeft;int oldT = mTop;int oldB = mBottom;int oldR = mRight;//通过之前介绍的 setFrame 方法进行赋值。boolean changed = isLayoutModeOptical(mParent) ?setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {onLayout(changed, l, t, r, b);if (shouldDrawRoundScrollbar()) {if(mRoundScrollbarRenderer == null) {mRoundScrollbarRenderer = new RoundScrollbarRenderer(this);}} else {mRoundScrollbarRenderer = null;}mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;ListenerInfo li = mListenerInfo;if (li != null && li.mOnLayoutChangeListeners != null) {ArrayList<OnLayoutChangeListener> listenersCopy =(ArrayList<OnLayoutChangeListener>)li.mOnLayoutChangeListeners.clone();int numListeners = listenersCopy.size();for (int i = 0; i < numListeners; ++i) {listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);}}}}
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1.3 小结

在之前的两篇文章 View 绘制体系知识梳理(3) - 绘制流程之 Measure 详解 和 View 绘制体系知识梳理(4) - 绘制过程之 Layout 详解，我们介绍了measure和layout的内部实现，而getMeasuredWidth和getWidth就分别对应于上面这两个阶段获得的宽度，也就是说：

• getMeasuredWidth是measure阶段获得的View的原始宽度。
• getWidth是layout阶段完成后，其在父容器中所占的最终宽度

1.4 注释说明

下面是Google文档中对于上面这两个方法的注释说明：

• getMeasuredWidth：

The width of this view as measured in the most recent call to measure().
This should be used during measurement and layout calculations only.
Use getWidth() to see how wide a view is after layout.Returns: the measured width of this view
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• getWidth

Return the width of the your view.Returns: the width of your view, in pixels
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二、示例

我们用一个简单的示例，来演示getMeasuredWidth和getWidth的区别：

2.1 布局定义

首先定义一个自定义的LinearLayout，它包含两个子View，在xml中它们的宽度都被指定为200dp。

<?xml version="1.0" encoding="utf-8"?>
<com.demo.lizejun.repoopt.WidthDemoLayoutxmlns:android="http://schemas.android.com/apk/res/android"android:orientation="vertical"android:layout_width="match_parent"android:layout_height="match_parent"><Viewandroid:background="@android:color/holo_blue_bright"android:layout_width="200dp"android:layout_height="100dp"/><Viewandroid:background="@android:color/holo_orange_light"android:layout_width="200dp"android:layout_height="100dp"/>
</com.demo.lizejun.repoopt.WidthDemoLayout>
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2.2 重写 onLayout 方法

在WidthDemoLayout中，我们重写它的onLayout方法，对它的子View重新摆放，并打印出getMeasuredWidth和getWidth方法的值：

public class WidthDemoLayout extends LinearLayout {public WidthDemoLayout(Context context) {super(context);}public WidthDemoLayout(Context context, @Nullable AttributeSet attrs) {super(context, attrs);}public WidthDemoLayout(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {super.onMeasure(widthMeasureSpec, heightMeasureSpec);}@Overrideprotected void onLayout(boolean changed, int l, int t, int r, int b) {super.onLayout(changed, l, t, r, b);int childCount = getChildCount();for (int i = 0; i < childCount; i++) {View child = getChildAt(i);if (i == childCount - 1) {child.layout(child.getLeft() ,child.getTop(), child.getRight() + 400, child.getBottom());}Log.d("WidthDemoLayout", "measuredWidth=" + child.getMeasuredWidth() + ",width=" + child.getWidth());}}
}
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输出的结果为：

>> 12-04 12:48:58.788 24935-24935/com.demo.lizejun.repoopt D/WidthDemoLayout: measuredWidth=800,width=800
>> 12-04 12:48:58.788 24935-24935/com.demo.lizejun.repoopt D/WidthDemoLayout: measuredWidth=800,width=1200
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最终展示的时候，虽然我们在xml中指定了相同的宽度，但是最终显示是以getWidth为准：

更多文章，欢迎访问我的 Android 知识梳理系列：

• Android 知识梳理目录：www.jianshu.com/p/fd82d1899…
• Android 面试文档分享：www.jianshu.com/p/8456fe6b2…