1 跟随手指移动的球

package ui;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by Administrator on 2016/4/3.
 */
public class MoveCircle extends View{
    public MoveCircle(Context context) {
        super(context);
    }

    public MoveCircle(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public MoveCircle(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    float currentX = 50.0f;
    float currentY = 50.0f;

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint = new Paint();
        paint.setColor(Color.RED);
        canvas.drawCircle(currentX,currentY,10,paint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        super.onTouchEvent(event);
        currentX = event.getX();
        currentY = event.getY();
        //重绘
        invalidate();
        return  true;

    }
}

<ui.MoveCircle
       android:id="@+id/circle"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:minHeight="100dp"
       android:minWidth="100dp"
       />