UI复习-自定义View（触摸画圆)

1>定义继承View的子类,根据业务需求重写View的方法

package com.brady.view;

import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.MotionEvent;
import android.view.View;

@SuppressLint("ClickableViewAccessibility")
public class DrawView extends View {

    //半径
    private int radius = 15;
    private float currentX = 25;
    private float currentY = 25;

    //创建画笔
    private Paint paint = new Paint();

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

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        currentX = event.getX();
        currentY = event.getY();

        //使整个View实现，如果View可见，则onDraw会被调用
        //This must be called from a UI thread. To call from a non-UI thread, call postInvalidate().
        invalidate();

        return true;
    }

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

}

引用该子类方式:

1>直接实例化添加

2>在xml中引用

<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: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"
    android:id="@+id/root"
    tools:context="com.brady.est.MainActivity" >
    <!-- 引入自定义组件 -->
    <com.brady.view.DrawView
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</LinearLayout>