今天要实现的是一个跟随手指的小球，说白了就是让小球按着手指滑动的轨迹运动，实现起来还是比较容易的。

用到的类是drawView，我们先自定义一个DrawView组件。

DrawView.java:

package cn.csdn.android.view;

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 = 300;
 public float currentY = 500;
 
 public DrawView(Context context) {
  super(context);
  // TODO Auto-generated constructor stub
 }

 @Override
 protected void onDraw(Canvas canvas) {
  // TODO Auto-generated method stub
  super.onDraw(canvas);
  Paint p = new Paint();
  p.setColor(Color.RED);
  canvas.drawCircle(currentX, currentY, 15, p);
 }
 
 
}

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在main.xml文件中给一个android:id="@+id/root";

然后写java代码实现跟踪效果：

CustomView.java

package cn.csdn.android.view;

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 CustomViewActivity extends Activity{

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  // TODO Auto-generated method stub
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  
  LinearLayout main = (LinearLayout) findViewById(R.id.root);
  final DrawView draw = new DrawView(this);
     draw.setMinimumWidth(300);
     draw.setMinimumHeight(500);
    
     draw.setOnTouchListener(new OnTouchListener() {
   
   @Override
   public boolean onTouch(View v, MotionEvent event) {
    draw.currentX = event.getX();
    draw.currentY = event.getY();
    draw.invalidate();
    return true;
   }
  });
     main.addView(draw);
 }
 
}