ViewTreeObserver示例(一)

main.xml如下:

<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
  >

    <TextView
        android:id="@+id/textview"
        android:layout_width="200dip"
        android:layout_height="100dip"
        android:text="@string/hello_world" 
        android:gravity="center"
        android:layout_centerInParent="true"
    />

</RelativeLayout>

MainActivity如下:

package cn.com.testviewtreeobserver1;
import android.os.Bundle;
import android.view.ViewTreeObserver;
import android.widget.TextView;
import android.app.Activity;
/**
 * 在Activity的onCreate()方法中
 * 利用ViewTreeObserver获取控件的高和宽
 */
public class MainActivity extends Activity {
    private TextView mTextView;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		init();
	}
   private void init(){
	   mTextView=(TextView) findViewById(R.id.textview);
	   //在onCreate()中获取控件的方法一(不可取)
	   int width=mTextView.getWidth();
	   int height=mTextView.getHeight();
	   System.out.println("方法一中---->width="+width+",height="+height);
	   //在onCreate()中获取控件的方法二(可行的)
	   ViewTreeObserver mViewTreeObserver = mTextView.getViewTreeObserver();
	   mViewTreeObserver.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
			public boolean onPreDraw() {
				int height = mTextView.getMeasuredHeight();
				int width = mTextView.getMeasuredWidth();
				System.out.println("方法二中---->width="+width+",height="+height);
				return true;
			}
		});
   }

}