Android使用ImageView实现支持手势缩放效果

2019-12-12 05:25:17

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TouchImageView继承自ImageView具有ImageView的所有功能；除此之外，还有缩放、拖拽、双击放大等功能，支持viewpager和scaletype，并伴有动画效果。

sharedConstructingprivate void sharedConstructing(Context context) {super.setClickable(true);this.context = context;mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());mGestureDetector = new GestureDetector(context, new GestureListener());matrix = new Matrix();prevMatrix = new Matrix();m = new float[9];normalizedScale = 1;if (mScaleType == null) {mScaleType = ScaleType.FIT_CENTER;}minScale = 1;maxScale = 3;superMinScale = SUPER_MIN_MULTIPLIER * minScale;superMaxScale = SUPER_MAX_MULTIPLIER * maxScale;setImageMatrix(matrix);setScaleType(ScaleType.MATRIX);setState(State.NONE);onDrawReady = false;super.setOnTouchListener(new PrivateOnTouchListener());}

初始化，设置ScaleGestureDetector的监听器为ScaleListener，这是用来处理缩放手势的，设置GestureDetector的监听器为GestureListener，这是用来处理双击和fling手势的，前两个手势都会引起图片的缩放，而fling会引起图片的移动。

mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());mGestureDetector = new GestureDetector(context, new GestureListener());

最后设置自定义View的touch事件监听器为PrivateOnTouchListener，这是touch事件的入口。

super.setOnTouchListener(new PrivateOnTouchListener());PrivateOnTouchListenerprivate class PrivateOnTouchListener implements OnTouchListener {//// Remember last point position for dragging//private PointF last = new PointF();@Overridepublic boolean onTouch(View v, MotionEvent event) {mScaleDetector.onTouchEvent(event);mGestureDetector.onTouchEvent(event);PointF curr = new PointF(event.getX(), event.getY());if (state == State.NONE || state == State.DRAG || state == State.FLING) {switch (event.getAction()) {case MotionEvent.ACTION_DOWN:last.set(curr);if (fling != null)fling.cancelFling();setState(State.DRAG);break;case MotionEvent.ACTION_MOVE:if (state == State.DRAG) {float deltaX = curr.x - last.x;float deltaY = curr.y - last.y;float fixTransX = getFixDragTrans(deltaX, viewWidth, getImageWidth());float fixTransY = getFixDragTrans(deltaY, viewHeight, getImageHeight());matrix.postTranslate(fixTransX, fixTransY);fixTrans();last.set(curr.x, curr.y);}break;case MotionEvent.ACTION_UP:case MotionEvent.ACTION_POINTER_UP:setState(State.NONE);break;}}setImageMatrix(matrix);//// User-defined OnTouchListener//if(userTouchListener != null) {userTouchListener.onTouch(v, event);}//// OnTouchImageViewListener is set: TouchImageView dragged by user.//if (touchImageViewListener != null) {touchImageViewListener.onMove();}//// indicate event was handled//return true;}}

触摸时会走到PrivateOnTouchListener的onTouch，它又会将捕捉到的MotionEvent交给mScaleDetector和mGestureDetector来分析是否有合适的callback函数来处理用户的手势。

mScaleDetector.onTouchEvent(event);mGestureDetector.onTouchEvent(event);

同时在当前状态是DRAG时将X、Y移动的距离赋值给变换矩阵

matrix.postTranslate(fixTransX, fixTransY);

给ImageView设置矩阵，完成X、Y的移动，即实现单指拖拽动作

setImageMatrix(matrix);

ScaleListener

private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {@Overridepublic boolean onScaleBegin(ScaleGestureDetector detector) {setState(State.ZOOM);return true;}@Overridepublic boolean onScale(ScaleGestureDetector detector) {scaleImage(detector.getScaleFactor(), detector.getFocusX(), detector.getFocusY(), true);//// OnTouchImageViewListener is set: TouchImageView pinch zoomed by user.//if (touchImageViewListener != null) {touchImageViewListener.onMove();}return true;}@Overridepublic void onScaleEnd(ScaleGestureDetector detector) {super.onScaleEnd(detector);setState(State.NONE);boolean animateToZoomBoundary = false;float targetZoom = normalizedScale;if (normalizedScale > maxScale) {targetZoom = maxScale;animateToZoomBoundary = true;} else if (normalizedScale < minScale) {targetZoom = minScale;animateToZoomBoundary = true;}if (animateToZoomBoundary) {DoubleTapZoom doubleTap = new DoubleTapZoom(targetZoom, viewWidth / 2, viewHeight / 2, true);compatPostOnAnimation(doubleTap);}}}

两指缩放动作会走到ScaleListener的回调，在它的onScale回调中会处理图片的缩放

scaleImage(detector.getScaleFactor(), detector.getFocusX(), detector.getFocusY(), true);

scaleImage

private void scaleImage(double deltaScale, float focusX, float focusY, boolean stretchImageToSuper) {float lowerScale, upperScale;if (stretchImageToSuper) {lowerScale = superMinScale;upperScale = superMaxScale;} else {lowerScale = minScale;upperScale = maxScale;}float origScale = normalizedScale;normalizedScale *= deltaScale;if (normalizedScale > upperScale) {normalizedScale = upperScale;deltaScale = upperScale / origScale;} else if (normalizedScale < lowerScale) {normalizedScale = lowerScale;deltaScale = lowerScale / origScale;}matrix.postScale((float) deltaScale, (float) deltaScale, focusX, focusY);fixScaleTrans();}

这里会将多次缩放的缩放比累积，并设置有最大和最小缩放比，不能超出范围

normalizedScale *= deltaScale;

最后把X、Y的缩放比和焦点传给变换矩阵，通过矩阵关联到ImageView，完成缩放动作

matrix.postScale((float) deltaScale, (float) deltaScale, focusX, focusY);

在onScaleEnd回调中，我们会判断是否当前缩放比超出最大缩放比或者小于最小缩放比，如果是，会有一个动画回到最大或最小缩放比状态

DoubleTapZoom doubleTap = new DoubleTapZoom(targetZoom, viewWidth / 2, viewHeight / 2, true);compatPostOnAnimation(doubleTap);

这里的动画DoubleTapZoom就是双击动画，关于DoubleTapZoom我们下面会讲到。至此两指缩放动作就完成了，下面继续看双击缩放动作。

GestureListener

private class GestureListener extends GestureDetector.SimpleOnGestureListener {@Overridepublic boolean onSingleTapConfirmed(MotionEvent e){if(doubleTapListener != null) {return doubleTapListener.onSingleTapConfirmed(e);}return performClick();}@Overridepublic void onLongPress(MotionEvent e){performLongClick();}@Overridepublic boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY){if (fling != null) {//// If a previous fling is still active, it should be cancelled so that two flings// are not run simultaenously.//fling.cancelFling();}fling = new Fling((int) velocityX, (int) velocityY);compatPostOnAnimation(fling);return super.onFling(e1, e2, velocityX, velocityY);}@Overridepublic boolean onDoubleTap(MotionEvent e) {boolean consumed = false;if(doubleTapListener != null) {consumed = doubleTapListener.onDoubleTap(e);}if (state == State.NONE) {float targetZoom = (normalizedScale == minScale) ? maxScale : minScale;DoubleTapZoom doubleTap = new DoubleTapZoom(targetZoom, e.getX(), e.getY(), false);compatPostOnAnimation(doubleTap);consumed = true;}return consumed;}@Overridepublic boolean onDoubleTapEvent(MotionEvent e) {if(doubleTapListener != null) {return doubleTapListener.onDoubleTapEvent(e);}return false;}}

在onDoubleTap回调中，设置双击缩放比，如果当前无缩放，则设置缩放比为最大值，如果已经是最大值，则设置为无缩放

float targetZoom = (normalizedScale == minScale) ? maxScale : minScale;

然后将当前点击坐标做为缩放中心，连同缩放比一起交给DoubleTapZoom，完成缩放动画

DoubleTapZoom doubleTap = new DoubleTapZoom(targetZoom, e.getX(), e.getY(), false);compatPostOnAnimation(doubleTap);

DoubleTapZoom

private class DoubleTapZoom implements Runnable {private long startTime;private static final float ZOOM_TIME = 500;private float startZoom, targetZoom;private float bitmapX, bitmapY;private boolean stretchImageToSuper;private AccelerateDecelerateInterpolator interpolator = new AccelerateDecelerateInterpolator();private PointF startTouch;private PointF endTouch;DoubleTapZoom(float targetZoom, float focusX, float focusY, boolean stretchImageToSuper) {setState(State.ANIMATE_ZOOM);startTime = System.currentTimeMillis();this.startZoom = normalizedScale;this.targetZoom = targetZoom;this.stretchImageToSuper = stretchImageToSuper;PointF bitmapPoint = transformCoordTouchToBitmap(focusX, focusY, false);this.bitmapX = bitmapPoint.x;this.bitmapY = bitmapPoint.y;//// Used for translating image during scaling//startTouch = transformCoordBitmapToTouch(bitmapX, bitmapY);endTouch = new PointF(viewWidth / 2, viewHeight / 2);}@Overridepublic void run() {float t = interpolate();double deltaScale = calculateDeltaScale(t);scaleImage(deltaScale, bitmapX, bitmapY, stretchImageToSuper);translateImageToCenterTouchPosition(t);fixScaleTrans();setImageMatrix(matrix);//// OnTouchImageViewListener is set: double tap runnable updates listener// with every frame.//if (touchImageViewListener != null) {touchImageViewListener.onMove();}if (t < 1f) {//// We haven't finished zooming//compatPostOnAnimation(this);} else {//// Finished zooming//setState(State.NONE);}}/*** Interpolate between where the image should start and end in order to translate* the image so that the point that is touched is what ends up centered at the end* of the zoom.* @param t*/private void translateImageToCenterTouchPosition(float t) {float targetX = startTouch.x + t * (endTouch.x - startTouch.x);float targetY = startTouch.y + t * (endTouch.y - startTouch.y);PointF curr = transformCoordBitmapToTouch(bitmapX, bitmapY);matrix.postTranslate(targetX - curr.x, targetY - curr.y);}/*** Use interpolator to get t* @return*/private float interpolate() {long currTime = System.currentTimeMillis();float elapsed = (currTime - startTime) / ZOOM_TIME;elapsed = Math.min(1f, elapsed);return interpolator.getInterpolation(elapsed);}/*** Interpolate the current targeted zoom and get the delta* from the current zoom.* @param t* @return*/private double calculateDeltaScale(float t) {double zoom = startZoom + t * (targetZoom - startZoom);return zoom / normalizedScale;}}

DoubleTapZoom其实是一个线程，实现了Runnable，我们直接看它的Run方法吧，这里定义了一个时间t

float t = interpolate();

其实t在500ms内通过一个加速差值器从0到1加速增长

private float interpolate() {long currTime = System.currentTimeMillis();float elapsed = (currTime - startTime) / ZOOM_TIME;elapsed = Math.min(1f, elapsed);return interpolator.getInterpolation(elapsed);}

通过t计算出当前缩放比

double deltaScale = calculateDeltaScale(t);

实现缩放

scaleImage(deltaScale, bitmapX, bitmapY, stretchImageToSuper);

然后根据当前t的值判断动画是否结束，如果t小于1，表示动画还未结束，重新执行本线程，否则设置状态完成。这里就是通过在这500ms内多次执行线程，多次重绘ImageView实现动画效果的。

if (t < 1f) {compatPostOnAnimation(this);} else {setState(State.NONE);}

同时在GestureListener的onFling回调中，设置Fling的X、Y速度，然后执行Fling的位移动画

fling = new Fling((int) velocityX, (int) velocityY);compatPostOnAnimation(fling);

Fling

private class Fling implements Runnable {CompatScroller scroller;int currX, currY;Fling(int velocityX, int velocityY) {setState(State.FLING);scroller = new CompatScroller(context);matrix.getValues(m);int startX = (int) m[Matrix.MTRANS_X];int startY = (int) m[Matrix.MTRANS_Y];int minX, maxX, minY, maxY;if (getImageWidth() > viewWidth) {minX = viewWidth - (int) getImageWidth();maxX = 0;} else {minX = maxX = startX;}if (getImageHeight() > viewHeight) {minY = viewHeight - (int) getImageHeight();maxY = 0;} else {minY = maxY = startY;}scroller.fling(startX, startY, (int) velocityX, (int) velocityY, minX,maxX, minY, maxY);currX = startX;currY = startY;}public void cancelFling() {if (scroller != null) {setState(State.NONE);scroller.forceFinished(true);}}@Overridepublic void run() {//// OnTouchImageViewListener is set: TouchImageView listener has been flung by user.// Listener runnable updated with each frame of fling animation.//if (touchImageViewListener != null) {touchImageViewListener.onMove();}if (scroller.isFinished()) {scroller = null;return;}if (scroller.computeScrollOffset()) {int newX = scroller.getCurrX();int newY = scroller.getCurrY();int transX = newX - currX;int transY = newY - currY;currX = newX;currY = newY;matrix.postTranslate(transX, transY);fixTrans();setImageMatrix(matrix);compatPostOnAnimation(this);}}}

Fling其实也是一个线程，实现了Runnable，根据Fling手势的X、Y速度我们会执行Scroller的fling函数，并且将当前位置设置为起始位置

scroller.fling(startX, startY, (int) velocityX, (int) velocityY, minX,maxX, minY, maxY);currX = startX;currY = startY;

再来看看Run函数，根据scroller当前滚动位置计算出新的位置信息，与旧位置相减得出在X、Y轴平移距离，实现平移

if (scroller.computeScrollOffset()) {int newX = scroller.getCurrX();int newY = scroller.getCurrY();int transX = newX - currX;int transY = newY - currY;currX = newX;currY = newY;matrix.postTranslate(transX, transY);fixTrans();setImageMatrix(matrix);compatPostOnAnimation(this);}

最后延时一段时间再次调用线程完成新的平移绘图，如此往复，直到scroller停止滚动，多次重绘ImageView实现了fling动画效果。

private void compatPostOnAnimation(Runnable runnable) {if (VERSION.SDK_INT >= VERSION_CODES.JELLY_BEAN) {postOnAnimation(runnable);} else {postDelayed(runnable, 1000/60);}}

下面看一看显示效果吧：

单个图片

这里写图片描述