CustomView的手势缩放总结

	OnScaleGestureListener listener = new OnScaleGestureListener() {
		
		@Override
		public void onScaleEnd(ScaleGestureDetector detector) {
			Log.i("OnScaleGestureListener", "onScaleEnd");
		}
		
		@Override
		public boolean onScaleBegin(ScaleGestureDetector detector) {
			Log.i("OnScaleGestureListener", "onScaleBegin");
			return true;
		}
		
		@Override
		public boolean onScale(ScaleGestureDetector detector) {
			Log.i("OnScaleGestureListener", "onScale");
			
			float dXStart = detector.getPreviousSpanX();
			float dXEnd = detector.getCurrentSpanX();
			float dScale = (dXEnd - dXStart) / getWidth();
			scale += dScale;
			if(scale > 3f) {
				scale = 3f;
			}
			if(scale < 1) {
				scale = 1f;
			}
			
//			Log.i("xFirstStart,xSecondStart,xFirstEnd", xFirstStart + "," + xSecondStart + "," + xFirstEnd + "," + xSecondEnd);
//			Log.i("dXStart,dXEnd,scale,kcvKchart.getWidth()", dXStart + "," + dXEnd + "," + scale + "," + kcvKchart.getWidth());
			setScaleX(scale);
			
			return false;
		}
	};

// 没有使用MotionEvent.ACTION_POINTER_DOWN事件
kcvKchart.setOnTouchListener(new OnTouchListener() {
			private float xFirstStart;
			private float xSecondStart;
			private float xFirstEnd;
			private float xSecondEnd;
			private int dXFirst;
			private int oldPointerCount;
			private int newPointerCount;
			private float scale = 1f;
			@Override
			public boolean onTouch(View v, MotionEvent event) {// can be written in KChartView‘s onTouchEven(--)
				switch (event.getAction()) {
				case MotionEvent.ACTION_DOWN:
					xFirstStart = event.getX();// to WindowScreen
					oldPointerCount = event.getPointerCount();
					
					break;
				case MotionEvent.ACTION_MOVE:
					newPointerCount = event.getPointerCount();
					if(newPointerCount == 1) {// one finger translate
						xFirstEnd = event.getX();
						dXFirst = Math.round(xFirstStart - xFirstEnd);// the closest integer to the argument,including positive & negative .  
						// TODO condition:if left x axis < 0 || right x axis > view.getWidth, then left x=0 || right x=view.getWidth return
						kcvKchart.scrollBy(dXFirst, 0); // can called repeatedly
//						Log.i("startX - endX, distanceX", xFirstStart - xFirstEnd + "," + dXFirst);
						xFirstStart = xFirstEnd;
					} else {// two or more finger scale
						xFirstEnd = event.getX();
						xSecondEnd = event.getX(1);
						if(oldPointerCount == 1) {// initialize second pointer axis
							// 由于第二个pointer的初始坐标不能再down事件中获取，只能在第一次move时获取，故第一次move不能进行缩放，需要过滤
							oldPointerCount = newPointerCount;
						} else {
							float dXStart = Math.abs(xFirstStart - xSecondStart);
							float dXEnd = Math.abs(xFirstEnd - xSecondEnd);
							float dScale = (dXEnd - dXStart) / kcvKchart.getWidth();
							scale += dScale;
							if(scale > 3f) {
								scale = 3f;
							}
							if(scale < 1) {
								scale = 1f;
							}
							
//							Log.i("xFirstStart,xSecondStart,xFirstEnd", xFirstStart + "," + xSecondStart + "," + xFirstEnd + "," + xSecondEnd);
//							Log.i("dXStart,dXEnd,scale,kcvKchart.getWidth()", dXStart + "," + dXEnd + "," + scale + "," + kcvKchart.getWidth());
							kcvKchart.setScaleX(scale);
						}
						xFirstStart = xFirstEnd;
						xSecondStart = xSecondEnd;
					}
					break;
				case MotionEvent.ACTION_POINTER_DOWN:
					
					break;
				default:
					break;
				}
				return true;
			}
		} );