[Android] 开发第十天

package com.oazzz.test7;

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;

public class DrawView extends View {
    public float currentX = 40;
    public float currentY = 50;
    // 定义 并创建画笔
    Paint p = new Paint();

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

    public DrawView(Context context, AttributeSet set) {
        super(context, set);
    }

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

    // 为该组件的触碰事件重写事件处理方法
    @Override
    public boolean onTouchEvent(MotionEvent event){
        // 修改 currentX 、 currentY 两个属性
        currentX = event.getX();
        currentY = event.getY();
        // 通知当前组件重绘自己
        invalidate();
        // 返回 true 表明该方法已经处理该事件
        return true;
    }
}

package com.oazzz.test7;

import android.os.Bundle;
import android.support.constraint.ConstraintLayout;
import android.support.v7.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    @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
        ConstraintLayout root = (ConstraintLayout)findViewById(R.id.root);
        // 创建 DrawView 组件
        final DrawView draw = new DrawView(this);
        // 设置自定义组件的最大宽度、高度
        draw.setMinimumWidth(300);
        draw.setMinimumHeight(500);
        root.addView(draw);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.oazzz.test7.MainActivity"
    android:id="@+id/root">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>