android脚步---跟随手指动的小球

package org.crazyit.helloworld;
import android.content.Context; 

import android.graphics.Canvas; 

import android.graphics.Color; 

import android.graphics.Paint; 

import android.view.View; 

public class DrawView extends View{
	   public float currentX=40; 

	    public float currentY=50; 

	     

	    //必须重写一个构造方法 

	    public DrawView(Context context) { 

	        super(context); 

	        // TODO Auto-generated constructor stub 

	    } 

	    //重写onDraw方法通过Canvas绘画 

	 

		@Override 

	    public void onDraw(Canvas canvas) {       

	        super.onDraw(canvas); 

	        //创建画笔 

	        Paint paint=new Paint(); 

	        paint.setColor(Color.RED); 

	        //绘制一个小圆 

	        canvas.drawCircle(currentX, currentY, 25, paint); 

	 

	    } 

}

package org.crazyit.helloworld;

import android.app.Activity; 
import android.os.Bundle; 
import android.util.Log;
import android.view.MotionEvent; 
import android.view.View; 
import android.widget.LinearLayout; 


public class MainActivity extends Activity {
	    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 

	        setContentView(R.layout.activity_main); 
	        LinearLayout root=(LinearLayout) findViewById(R.id.root); 
	        //创建一个自己继承于View的对象 

	        final DrawView drawView=new DrawView(this); 

	        //设置自定义组件的最大宽度和高度 

	        drawView.setMinimumWidth(300); 

	        drawView.setMinimumHeight(500); 
            //为drawview组件绑定tounch事件
	        drawView.setOnTouchListener(new View.OnTouchListener() {     

	            public boolean onTouch(View v, MotionEvent event) { 
	            	Log.e("onTouch", "onTouch");

	                drawView.currentX=event.getX(); 

	                drawView.currentY=event.getY();  

	                //通知drawview组件重绘 

	                drawView.invalidate(); 

	                //返回true表明算是方法已经处理该事件 

	                return true; 

	            } 

	        }); 

	        root.addView(drawView); 

	    }
	}

<LinearLayout 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" 

    android:orientation="vertical"  

    android:background="#00FFCC" //定义背景颜色

    android:id="@+id/root"> 

</LinearLayout>