跟随手指的小球

    

Crize_demo\draw_demo\src\main\java\com\ly\draw_demo\DrawView.java

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;

    public DrawView(Context context) {
        super(context);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //创建画笔
        Paint paint = new Paint();
        //设置画笔的颜色
        paint.setColor(Color.RED);
        //绘制一个小圆(作为小球)
        canvas.drawCircle(currentX,currentY,15,paint);
    }
}

Crize_demo\draw_demo\src\main\res\layout\activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:id="@+id/root"
    tools:context=".MainActivity">

</LinearLayout>

Crize_demo\draw_demo\src\main\java\com\ly\draw_demo\MainActivity.java

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

public class MainActivity extends Activity {
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //获取布局文件中的LinearLayout容器
        LinearLayout root = (LinearLayout) findViewById(R.id.root);
        //创建DrawView组件
        final DrawView drawView = new DrawView(this);
        //设置自定义框架的宽度和高度
        drawView.setMinimumWidth(300);
        drawView.setMinimumHeight(500);
        //为drawView绑定Touch事件(触摸屏幕的监听事件)
        drawView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                //修改drawView组件的currentX,currentY两个属性
                drawView.currentX = event.getX();
                drawView.currentY = event.getY();
                //通知drawView组件重绘
                drawView.invalidate();
                //返回true表明处理方法已经处理该事件
                return true;
            }
        });
        root.addView(drawView);
    }


}