自定義view 製造水波紋的效果

要自定義View可以創一個新的class去繼承View這個類，

之後針對需要定義一些自己要的功能，

這裡提供一個類似水波紋效果的code。

	import android.content.Context;
	import android.graphics.Canvas;
	import android.graphics.Paint;
	import android.util.AttributeSet;
	import android.view.MotionEvent;
	import android.view.View;
	import java.util.ArrayList;
	import android.os.Handler;
	import java.util.logging.LogRecord;
	import static java.lang.StrictMath.abs;
	import static java.lang.StrictMath.pow;
	import static java.lang.StrictMath.sqrt;
	public class MyWave extends View {
	private ArrayList<Wave> wList;
	Handler handler = new Handler();
	int positionX=0;
	int positionY=0;
	public MyWave(Context context, AttributeSet attrs) {
	super(context, attrs);
	wList = new ArrayList<Wave>();
	handler.postDelayed(callOnDraw,100);
	}
	@Override
	protected void onDraw(Canvas canvas) {
	super.onDraw(canvas);
	for (int i = 0; i < wList.size(); i++) {
	Wave wave = wList.get(i);
	canvas.drawCircle(wave.pointX, wave.pointY, wave.radius, wave.paint);
	}
	}
	private class Wave {
	//圓心
	int pointX;
	int pointY;
	//畫筆
	Paint paint=new Paint();
	//半徑
	int radius;
	}
	@Override
	public boolean onTouchEvent(MotionEvent event) {
	super.onTouchEvent(event);
	switch (event.getAction()) {
	case MotionEvent.ACTION_DOWN:
	case MotionEvent.ACTION_MOVE:
	int x = (int) event.getX();
	int y = (int) event.getY();
	Wave temp = new Wave();
	double dis = sqrt(pow((positionX-x),2)+pow((positionY-y),2));
	temp.pointX = x;
	temp.pointY = y;
	temp.paint.setAlpha(100);
	temp.radius = 0;
	if(dis > 30){
	wList.add(temp);
	positionX = x;
	positionY = y;
	}
	// System.out.println(x);
	}
	return true;
	}
	private Runnable callOnDraw = new Runnable() {
	@Override
	public void run() {
	invalidate();
	System.out.println(wList.size()+" size");
	for(int i = 0 ;i<wList.size();i++){
	wList.get(i).radius = wList.get(i).radius +10;
	wList.get(i).paint.setAlpha(wList.get(i).paint.getAlpha() - 10);
	if(wList.get(i).paint.getAlpha() < 5){
	wList.remove(i);
	i--;
	}
	}
	handler.postDelayed(this,100);
	}
	};
	}

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