自定义view——随手指移动的小球

参考《Android疯狂讲义》（第三版）2.1。

 

核心代码：自定义View类——继承View，重写OnDraw(Canvas canvas)和onTouchEvent(MotionEvent event)两个方法。

package yuhao.user_defined_view.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 Yuhao on 2016/10/11.
 */
public class View_BallMoveFollowFinger extends View {
    public float currentX = 40;
    public float currentY = 50;
    //定义并创建画笔
    Paint paint = new Paint();
    public View_BallMoveFollowFinger(Context context){
        super(context);
    }
    public View_BallMoveFollowFinger(Context context, AttributeSet set){
        super(context, set);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //设置画笔颜色
        paint.setColor(Color.GREEN);
        canvas.drawCircle(currentX, currentY, 30, paint);
    }
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        //修改currentX, currentY的值
        currentX = event.getX();
        currentY = event.getY();
        //通知当前组件重绘自身
        invalidate();
        //返回true表明该处理方法已经处理该事件
        return true;
    }
}

 

 

自定义符合我们所需功能的View后，其它用法与我们常用的TextView、Button等类似。在XML加入自定义View组件如下（15-17行）：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_ball_move_follow_finger"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context="yuhao.user_defined_view.BallMoveFollowFinger">
    <!-- 加入自定义组件 -->
    <yuhao.user_defined_view.ui.View_BallMoveFollowFinger
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

 

 

如果不在XML中引入，我们也可以通过JAVA代码添加：

package yuhao.user_defined_view;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.LinearLayout;
import yuhao.user_defined_view.ui.View_BallMoveFollowFinger;
public class BallMoveFollowFinger extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_ball_move_follow_finger);
        //以下为不在布局中加入自定义组件而在Java代码中添加的方法
        LinearLayout ll_bmff = (LinearLayout) findViewById(R.id.activity_ball_move_follow_finger);
        //创建View_BallMoveFollowFinger组件并设置最小高宽
        View_BallMoveFollowFinger view_ballMoveFollowFinger = new View_BallMoveFollowFinger(this);
        view_ballMoveFollowFinger.setMinimumHeight(300);
        view_ballMoveFollowFinger.setMinimumWidth(500);
        //将View_BallMoveFollowFinger添加到布局中
        ll_bmff.addView(view_ballMoveFollowFinger);
    }
}

 

 

效果图：