单个水波纹

paint的使用

<RelativeLayout 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"
    tools:context=".MainActivity" >

    <com.itheima.wave28.MyRring
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />

</RelativeLayout>

package com.itheima.wave28;

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

public class MyRring extends View{

	/**
	 * 圆环圆心的X坐标
	 */
	private int cx;

	/**
	 * 圆环圆心的Y坐标
	 */
	private int cy;

	private Paint paint;

	/**
	 * 圆环的半径
	 */
	private float radius;

	/**
	 * 线条的厚度
	 */
	private float strokeWidth;

	public MyRring(Context context, AttributeSet attrs) {
		super(context, attrs);

		initView();
	}

	private void initView() {
		//初始化paint
		paint = new Paint();
		paint.setAntiAlias(true); // 抗矩齿
		paint.setColor(Color.RED);
		paint.setStyle(Style.STROKE); //刻画，画线条  默认的是Fill状态，就是填充颜色
		paint.setStrokeWidth(strokeWidth); //设置条线的厚度
		paint.setAlpha(255); //设置透明度 ，0--255  0代表完全透明

		//
		this.radius =0;
		strokeWidth = 0;
	}

	@Override
	/**
	 * 绘制我们的内容
	 */
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);

		/**
		 * 绘制圆环
		 * 由onTouchEvent获取圆心 就是点击下去时的位置
		 */
		canvas.drawCircle(cx, cy, radius, paint);

	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		super.onTouchEvent(event);

		switch (event.getAction()) {
		case MotionEvent.ACTION_DOWN: // 点击，获得圆环的中心
			cx = (int) event.getX();
			cy = (int) event.getY();
			//初始化画笔
			initView();
			handler.sendEmptyMessage(0);
			break;
		}

		return true;
	}

	/*
	 * 刷新状态
	 */
	private void flushState() {

		this.radius+=10;
		this.strokeWidth = radius/4;
		paint.setStrokeWidth(strokeWidth);

		int nextAlpha = paint.getAlpha()-20;

		//小于20再减就负数了  所以直接等于0即可
		if(nextAlpha<=20){
			nextAlpha = 0;
		}
		paint.setAlpha(nextAlpha);

	}

	private Handler handler = new Handler(){
		public void handleMessage(android.os.Message msg) {

			//刷新状态
			flushState();
			// 刷新页面 执行onDraw()方法绘制
			invalidate();

			if(paint.getAlpha() !=0){
				//第二参数是延迟时间
				handler.sendEmptyMessageDelayed(0, 100);
			}
		};
	};

	@Override
	/**
	 * 大小的测量按系统的默认规则
	 * 默认规则就是在xml布局里面定义的
	 * android:layout_width="match_parent"
     * android:layout_height="match_parent"
	 */
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);
	}

}