Android简易实战教程--第五十三话《多彩波浪》

今天带来一篇自定义View的小案例，点击屏幕随机生成五颜六色的波浪效果。逻辑十分简单，Demo挺有趣，直接代码分享在下面：

public class MyWaveView extends View {

	List<Wave> waveList = new ArrayList<MyWaveView.Wave>();
	List<Wave> currentList = new ArrayList<MyWaveView.Wave>();
	
	private int alpha;

	int[] colors = new int[] { Color.BLUE, Color.RED, Color.GREEN, Color.YELLOW ,Color.GRAY,Color.LTGRAY};

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

			flushData();

			if (!waveList.isEmpty()) {// 集合若为空没必要发消息
				// 发延时消息，形成循环
				handler.sendEmptyMessageDelayed(0, 80);
			}

			// 刷新界面
			invalidate();
		}
	};
	
	private void flushData() {
		
		for (Wave wave : waveList) {
			// 半径增加
			wave.radius += 3;
			wave.paint.setStrokeWidth(wave.radius / 3);

			alpha = wave.paint.getAlpha();

			if (alpha <= 0) {
				// 当前wave消失，集合移除该对象，放置内存溢出
				currentList.add(wave);
				continue;
			}
			// 透明度降低
			alpha -= 5;
			if (alpha < 0) {
				alpha = 0;
			}

			wave.paint.setAlpha(alpha);
		}
		//统一移除
		waveList.remove(currentList);
	}

	public MyWaveView(Context context) {
		this(context, null);
	}

	public MyWaveView(Context context, AttributeSet attrs) {
		super(context, attrs);
	}

	/**
	 * 随机获取颜色值
	 * 
	 * @return
	 */
	private int getRandomColor() {
		Random random = new Random();
		int n = random.nextInt(colors.length);
		return colors[n];
	}

	@Override
	protected void onDraw(Canvas canvas) {
		for (Wave wave : waveList) {
			canvas.drawCircle(wave.cx, wave.cy, wave.radius, wave.paint);
		}
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		switch (event.getAction()) {
		case MotionEvent.ACTION_DOWN:
		case MotionEvent.ACTION_MOVE:
			int cx = (int) event.getX();
			int cy = (int) event.getY();

			initWave(cx, cy);
			break;

		default:
			break;
		}
		return true;
	}

	/**
	 * 封装波浪信息
	 * 
	 * @param cx
	 * @param cy
	 */
	private void initWave(int cx, int cy) {
		if (waveList.isEmpty()) {// 第一次添加Wave对象

			addWave(cx, cy);

			// 发消息展示“动画”
			handler.sendEmptyMessage(0);
		} else {
			//获取上一次的最后一个波浪实例
			Wave lastWave = waveList.get(waveList.size() - 1);
			
			if(Math.abs(cx - lastWave.cx)>8 || Math.abs(cy - lastWave.cy)>8){
				addWave(cx, cy);
			}
			// 第一次已经发了消息，不必再去发消息
		}

	}

	/**
	 * 创建Wave对象，并添加到集合
	 * 
	 * @param cx
	 * @param cy
	 */
	private void addWave(int cx, int cy) {
		Wave wave = new Wave();
		wave.cx = cx;
		wave.cy = cy;

		Paint paint = new Paint();

		paint.setColor(getRandomColor());
		paint.setAntiAlias(true);
		// Style.STROKE:表示空心
		paint.setStyle(Style.STROKE);

		wave.paint = paint;

		waveList.add(wave);
	}

	/**
	 * 波纹的封装类,一个波纹代表一个对象
	 * 
	 * @author lenovo
	 * 
	 */
	public class Wave {
		public float radius;
		public int cx;
		public int cy;

		public Paint paint;
	}
}

关注本专栏，不定期更新简单有趣的小案例哦~

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