View的onMeasure方法

最新推荐文章于 2022-07-06 11:40:45 发布

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本文介绍了Android中View.MeasureSpec类的使用方法，详细解释了MeasureSpec如何帮助确定View的宽度和高度规格。通过具体代码示例展示了如何获取MeasureSpec的模式和大小。

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View.MeasureSpec类中的常量：

private static final int MODE_SHIFT = 30;
public static final int UNSPECIFIED = 0 << MODE_SHIFT;//0
public static final int EXACTLY     = 1 << MODE_SHIFT;//1073741824
public static final int AT_MOST     = 2 << MODE_SHIFT;//-2147483648

由onMeasure方法带的参数widthMeasureSpec、heightMeasureSpec，得到View的尺寸的规格和大小：

int specMode = MeasureSpec.getMode(measureSpec);//UNSPECIFIED，EXACTLY，AT_MOST
int specSize = MeasureSpec.getSize(measureSpec);

实例代码

public class TestView extends View {

	public TestView(Context context, AttributeSet attrs) {
		super(context, attrs);
		// TODO Auto-generated constructor stub
	}
	public TestView(Context context) {
		super(context);
		// TODO Auto-generated constructor stub
	}
	@Override
	public void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		Log.v("view.onMeasure", "widthMeasureSpec="+widthMeasureSpec);
		Log.v("view.onMeasure", "heightMeasureSpec="+heightMeasureSpec);
		
		int widthMode = MeasureSpec.getMode(widthMeasureSpec);
		int heightMode = MeasureSpec.getMode(heightMeasureSpec);
		int widthSize = MeasureSpec.getSize(widthMeasureSpec);
		int heightSize = MeasureSpec.getSize(heightMeasureSpec);
		
		Log.v("view.onMeasure", "widthMode="+widthMode);
		Log.v("view.onMeasure", "heightMode="+heightMode);
		Log.v("view.onMeasure", "widthSize="+widthSize);
		Log.v("view.onMeasure", "heightSize="+heightSize);
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);
	}
}

<LinearLayout 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.example.viewlearning.MainActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />
	<com.example.viewlearning.TestView 
	    android:layout_width="50dp"
	    android:layout_height="50dp"
	    android:background="#666666"/>
</LinearLayout>