挥动的小球

编写时遇到的问题：声明int变量时没有声明public，在重写ondraw方法时。没有继承，并且没有canvas；布局时Lineration写在了外面；重绘的语句不会写；

第一个文件：

package com.android.test;

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 x;
  public  float y;
 public DrawView(Context context) {
  super(context);
  // TODO Auto-generated constructor stub
 }
 public void onDraw(Canvas canvas){
  super.onDraw(canvas);
  Paint paint =new Paint();
  paint.setColor(Color.GREEN);
  canvas.drawCircle(x,y, 15, paint);
 
 }
}

第二个文件：

package com.android.test;

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

public class MoveBallActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
   
    LinearLayout layout =(LinearLayout)findViewById(R.id.root);
    final DrawView drawView =new DrawView(this);
    drawView.setMinimumHeight(400);
    drawView.setMinimumWidth(400);
    drawView.setOnTouchListener(new OnTouchListener() {
  
  @Override
  public boolean onTouch(View v, MotionEvent event) {
   drawView.x= event.getX();
   drawView.y= event.getY();
     drawView.invalidate();
   return true;
  }
 });
    layout.addView(drawView);
}
}