android 定时器与Canvas结合使用

根据别人的例子自己写了，并理解了下

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
   
    <LinearLayout android:id="@+id/LinearLayout01"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content">
        
  <Button android:id="@+id/Button01"
    android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:text="Button1"
     />
     
     <Button android:id="@+id/Button02"
    android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:text="Button2"
     />
          
    </LinearLayout>
       
        <SurfaceView android:id="@+id/SurfaceView01"
      android:layout_width="fill_parent"
         android:layout_height="fill_parent"
  />
</LinearLayout>

package MyTestSurfaceView.code;

import java.util.Timer;
import java.util.TimerTask;

import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {
    /** Called when the activity is first created. */

 private Button btnSimpleDraw;
 private Button btnTimerDraw;
 private SurfaceView sfv;
 private SurfaceHolder sfh;
 
 private Timer mTimer;
 private MyTimerTask mTimerTask;
 int Y_axis[],centerY,oldX,oldY,currentX;
 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        btnSimpleDraw = (Button)findViewById(R.id.Button01);
        btnTimerDraw = (Button)findViewById(R.id.Button02);
        btnSimpleDraw.setOnClickListener(new ClickEvent());
        btnTimerDraw.setOnClickListener(new ClickEvent());
       
        sfv = (SurfaceView)findViewById(R.id.SurfaceView01);
        sfh = sfv.getHolder();
       
        mTimer = new Timer();
        mTimerTask = new MyTimerTask();
       
        centerY = (getWindowManager().getDefaultDisplay().getHeight() - sfv.getTop())/ 2 ;
        Y_axis = new int[getWindowManager().getDefaultDisplay().getWidth()];
        oldX = 0;
        oldY = 0;
               
        for( int i = 1; i < Y_axis.length; ++ i )
        {
         Y_axis[i-1] = centerY - (int)(100*Math.sin(i*2*Math.PI/180));
        }
    }

    class ClickEvent implements View.OnClickListener
    {
     @Override
     public void onClick(View v )
     {
      if( v == btnSimpleDraw )
      {
       SimpleDraw(Y_axis.length - 1 );
      }
      else if( v == btnTimerDraw )
      {
       oldY = centerY;
       mTimer.schedule(mTimerTask,0,50);
      }
     }
    }
   
   
    class MyTimerTask extends TimerTask
    {
     @Override
     public void run()
     {
      SimpleDraw(currentX);
      ++currentX;
      
      if( currentX == Y_axis.length - 1 )
      {
       ClearDraw();
       currentX = 0;
       oldY = centerY;
      }
     }
    }
   
   
    void SimpleDraw( int length )
    {
     if( length == 0 )
     {
      oldX = 0;
     }
         
     Canvas canvas = sfh.lockCanvas( new Rect(oldX,0,oldX + length , getWindowManager().getDefaultDisplay().getHeight()));
     
     Paint paint = new Paint();
     paint.setColor(Color.GREEN);
     paint.setStrokeWidth(2);
     
     int y;
     for( int i = oldX + 1; i < length; ++ i )
     {
      y = Y_axis[i-1];
      canvas.drawLine(oldX,oldY,i,y,paint);
      Log.i("Rollrock" , "Line:" + oldX + " " + oldY + "  " + i + "  " + y );
      oldX = i;
      oldY = y;
     }

　　
     
     sfh.unlockCanvasAndPost(canvas);
    }
   
    private void ClearDraw()
    {
     Canvas canvas = sfh.lockCanvas(null);
     canvas.drawColor(Color.BLACK);
     sfh.unlockCanvasAndPost(canvas);
    }
}

  附: 虽然在 xml里面我们可以看到  SurfaceView01 android:layout_height="fill_parent" ，但是通过实际的数据发现，canvas的y坐标的0点再button的下方。