<?xml version="1.0" encoding="utf-8"?> 
 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
android:layout_width="fill_parent" 
android:layout_height="fill_parent" 
android:orientation="vertical" 
> 
 
<SurfaceView 
android:id="@+id/surfaceview"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_above="@+id/line"
android:layout_alignParentTop="true"
/>
 
<LinearLayout
android:id="@+id/line"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
>
 
<Button
android:id="@+id/flushbutton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="清屏"
/>
 
<Button
android:id="@+id/colorbutton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1" 
android:text="颜色"
/>
</LinearLayout>
</RelativeLayout> 

package com.nan.wall;   
   
import android.app.Activity;   
import android.app.AlertDialog;   
import android.app.Dialog;   
import android.content.DialogInterface;   
import android.graphics.Canvas;   
import android.graphics.Color;   
import android.graphics.Paint;   
import android.graphics.Rect;   
import android.os.Bundle;   
import android.view.MotionEvent;   
import android.view.SurfaceHolder;    
import android.view.SurfaceView;   
import android.view.View;    
import android.widget.Button;    
   
public class MyWallActivity extends Activity    
{    
private SurfaceView mSurfaceView = null;    
private SurfaceHolder mSurfaceHolder = null;    
private Button cleanButton = null;    
private Button colorButton = null;    
   
private float oldX = 0f;    
private float oldY = 0f;    
   
private boolean canDraw = false;   
private Paint mPaint = null;   
//用来记录当前是哪一种颜色    
private int whichColor = 0;    
   
/** Called when the activity is first created. */   
  @Override    
public void onCreate(Bundle savedInstanceState)    
{    
super.onCreate(savedInstanceState);   
setContentView(R.layout.main);   
      
mSurfaceView = (SurfaceView)this.findViewById(R.id.surfaceview);   
mSurfaceHolder = mSurfaceView.getHolder();   
   
mPaint = new Paint();    
//画笔的颜色    
mPaint.setColor(Color.RED);    
//画笔的粗细    
mPaint.setStrokeWidth(2.0f);   
cleanButton = (Button)this.findViewById(R.id.flushbutton);    
//按钮监听    
cleanButton.setOnClickListener(new View.OnClickListener()    
{    
   
@Override    
public void onClick(View v)    
{    
// TODO Auto-generated method stub    
//锁定整个SurfaceView    
Canvas mCanvas = mSurfaceHolder.lockCanvas();    
mCanvas.drawColor(Color.BLACK);    
//绘制完成，提交修改   
mSurfaceHolder.unlockCanvasAndPost(mCanvas);    
//重新锁一次    
mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));    
mSurfaceHolder.unlockCanvasAndPost(mCanvas);    
}   
});     
   
colorButton = (Button)this.findViewById(R.id.colorbutton);   
//按钮监听    
colorButton.setOnClickListener(new View.OnClickListener()    
{    
   
@Override    
public void onClick(View v)    
{    
 // TODO Auto-generated method stub   
   
Dialog mDialog = new AlertDialog.Builder(MyWallActivity.this)    
.setTitle("颜色设置")    
.setSingleChoiceItems(new String[]{"红色","绿色","蓝色"}, whichColor, new DialogInterface.OnClickListener()    
{    
@Override   
public void onClick(DialogInterface dialog, int which)    
{    
 // TODO Auto-generated method stub    
switch(which)    
{    
case 0:    
{    
//画笔的颜色    
mPaint.setColor(Color.RED);    
whichColor = 0;    
break;    
}    
case 1:    
{    
//画笔的颜色   
mPaint.setColor(Color.GREEN);   
whichColor = 1;   
break;   
}   
case 2:   
{   
//画笔的颜色106                 
mPaint.setColor(Color.BLUE);   
whichColor = 2;                 
break;                 
}   
}   
}   
})   
.setPositiveButton("确定", new DialogInterface.OnClickListener()   
{   
@Override   
public void onClick(DialogInterface dialog, int which)    
{   
// TODO Auto-generated method stub   
dialog.dismiss();   
}   
})   
.create();   
mDialog.show();   
}   
});   
   
   
@Override   
public boolean onTouchEvent(MotionEvent event)   
{      
//获取x坐标   
float x = event.getX();   
//获取y坐标（不知道为什么要减去一个偏移值才对得准屏幕）   
float y = event.getY()-50;   
//第一次进来先不管   
if(canDraw)   
{      
//获取触屏事件   
switch(event.getAction())   
{   
//如果是拖动事件   
case MotionEvent.ACTION_MOVE:   
{   
//锁定整个SurfaceView   
Canvas mCanvas = mSurfaceHolder.lockCanvas();     
mCanvas.drawLine(x, y, oldX, oldY, mPaint);   
mSurfaceHolder.unlockCanvasAndPost(mCanvas);   
//重新锁一次   
mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));   
mSurfaceHolder.unlockCanvasAndPost(mCanvas);   
break;   
}   
}   
}   
//保存目前的x坐标值   
oldX = x;   
//保存目前的y坐标值   
oldY = y;   
   
canDraw = true;   
   
return true;   
}   
   
}