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前两篇文章讲解了Android的触控机制和手势操作，讲到多点触控时我们举了一个简单的手势缩放图片的例子，但是功能很有限。本篇我们通过解析一个国外大牛Mike Ortiz写的自定义TouchImageView的源码，来更加深入了解安卓触控和手势操作。
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。
private 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());private class PrivateOnTouchListener implements OnTouchListener {
//
// Remember last point position for dragging
//
private PointF last = new PointF();
@Override
public 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);private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
@Override
public boolean onScaleBegin(ScaleGestureDetector detector) {
setState(State.ZOOM);
return true;
}
@Override
public 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;
}
@Override
public 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); 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。
private class GestureListener extends GestureDetector.SimpleOnGestureListener {
@Override
public boolean onSingleTapConfirmed(MotionEvent e)
{
if(doubleTapListener != null) {
return doubleTapListener.onSingleTapConfirmed(e);
}
return performClick();
}
@Override
public void onLongPress(MotionEvent e)
{
performLongClick();
}
@Override
public 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);
}
@Override
public 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;
}
@Override
public 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); 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);
}
@Override
public 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); 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);
}
}
@Override
public 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
图片加载到ViewPager中
镜像图片
点击可改变图片
点击可改变ScaleType
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原文地址：http://blog.csdn.net/huaxun66/article/details/52386678
