下面是我的测试程序, 重写了 View 中的 getDefaultSize 方法，打印出每次调用 getDefaultSize 的时候传递进来的 measureSpec 的模式，在主 activity 的 xml 中放了 3 个 TestView，分别使用 wrap_content、match_parent、具体 dp 值，来指定 layout_width 和 layout_height 的值，期望通过 log 看到 3 个 view 在调用自己的 onMeasure 方法的时候传递进来的测量约束的模式。但是打印结果让我很糊涂，因为打印的结果和设置的值看起来并不是一一对应的关系？所以我想问，测量模式和 layout_width 的值的类型是到底什么对应关系？
MainActivity 布局文件如下：
<RelativeLayout 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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.testmeasurespec.MainActivity" >
<com.example.testmeasurespec.TestView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@drawable/ic_launcher"
android:tag="test1" />
<com.example.testmeasurespec.TestView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/ic_launcher"
android:tag="test2" />
<com.example.testmeasurespec.TestView
android:layout_width="20dp"
android:layout_height="20dp"
android:background="@drawable/ic_launcher"
android:tag="test3" />
</RelativeLayout>
测试 TestView 类如下：
public class TestView extends View {
private static final String TAG = "TestView";
public TestView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
public TestView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public TestView(Context context) {
super(context);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// TODO Auto-generated method stub
Log.i(TAG, "onMeasure:" + getTag());
setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
}
public static int getDefaultSize(int size, int measureSpec) {
int result = size;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
switch (specMode) {
case MeasureSpec.UNSPECIFIED:
Log.i(TAG, "specMode:MeasureSpec.UNSPECIFIED");
result = size;
break;
case MeasureSpec.AT_MOST:
Log.i(TAG, "specMode:MeasureSpec.AT_MOST");
case MeasureSpec.EXACTLY:
Log.i(TAG, "specMode:MeasureSpec.EXACTLY");
result = specSize;
break;
}
return result;
}
}
打印结果如下：
11-21 16:13:48.812: I/TestView(21213): onMeasure:test3
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.AT_MOST
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.812: I/TestView(21213): onMeasure:test2
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.812: I/TestView(21213): onMeasure:test1
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.AT_MOST
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.AT_MOST
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.812: I/TestView(21213): onMeasure:test3
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.812: I/TestView(21213): onMeasure:test2
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.812: I/TestView(21213): onMeasure:test1
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.AT_MOST
11-21 16:13:48.812: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.892: I/TestView(21213): onMeasure:test3
11-21 16:13:48.892: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.892: I/TestView(21213): specMode:MeasureSpec.AT_MOST
11-21 16:13:48.892: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.892: I/TestView(21213): onMeasure:test2
11-21 16:13:48.892: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.892: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.902: I/TestView(21213): onMeasure:test1
11-21 16:13:48.902: I/TestView(21213): specMode:MeasureSpec.AT_MOST
11-21 16:13:48.902: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.902: I/TestView(21213): specMode:MeasureSpec.AT_MOST
11-21 16:13:48.902: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.902: I/TestView(21213): onMeasure:test3
11-21 16:13:48.902: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.902: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.902: I/TestView(21213): onMeasure:test2
11-21 16:13:48.902: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.902: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.902: I/TestView(21213): onMeasure:test1
11-21 16:13:48.902: I/TestView(21213): specMode:MeasureSpec.EXACTLY
11-21 16:13:48.902: I/TestView(21213): specMode:MeasureSpec.AT_MOST
11-21 16:13:48.902: I/TestView(21213): specMode:MeasureSpec.EXACTLY
最簡單的映射關係是：
* wrap_parent -> MeasureSpec.AT_MOST
* match_parent -> MeasureSpec.EXACTLY
* 具體值 -> MeasureSpec.EXACTLY
但上面程式碼由於放在RelativeLayout 中，RelativeLayout 是一個比較複雜的ViewGroup，其中子view 的大小不僅跟layout_width、layout_height 屬性相關，還更很多屬性有關係，所以會改變上述映射情況，使結果變得特別複雜。