Android 中View.onDraw(Canvas canvas)的使用方法

<?xml version="1.0" encoding="utf-8"?  
<FrameLayout 
  android:layout_width="fill_parent" 
  android:layout_height="fill_parent" 
  xmlns:android="http://schemas.android.com/apk/res/android"  
  <com.android.test.TestView 
    android:id="@+id/testview" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent"/  
</FrameLayout  

package com.android.test; 
import android.app.Activity; 
import android.content.Context; 
import android.graphics.Canvas; 
import android.graphics.Color; 
import android.graphics.Paint; 
import android.graphics.Rect; 
import android.graphics.Typeface; 
import android.os.Bundle; 
import android.view.View; 
public class TestActivity extends Activity { 
  /** Called when the activity is first created. */ 
  @Override 
  public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(new TestView(this)); 
  } 
  public class TestView extends View { 
    private Paint mPaint = new Paint(); 
    public TestView(Context context) { 
      super(context); 
    } 
     
    @Override 
    protected void onDraw(Canvas canvas) { 
      // TODO Auto-generated method stub 
      super.onDraw(canvas); 
       
      String text = "Android - 机器人";      
      mPaint.setColor(Color.WHITE); 
       
      Paint paint = new Paint(); 
      paint.setColor(Color.RED); 
       
      String familyName = "宋体"; 
      Typeface font = Typeface.create(familyName,Typeface.BOLD); 
      paint.setTypeface(font); 
       
      paint.setTextSize(22); 
       
      canvas.drawRect(new Rect(0, 0, 320, 240), mPaint); 
      canvas.drawText(text, 0, 100, paint); 
    } 
  } 
}