可以看到，我们进行了两步判断，从而获得合适的宽高值，然后将图片进行布局，在自动布局时将图片中心与裁剪区域中心重合，最后我们会得到下面的效果图
支持移动和缩放图片
正如上面所讲，由于图片在裁剪区域内是以类似 UIViewContentModeScaleAspectFill 的方式放置的，很可能出现部分内容溢出裁剪区域，因此我们要让图片能支持动态移动和缩放，从而使用户能灵活地裁剪图片的内容。
具体实现上，我们其实是在 cropview 上加上手势，间接操作图片的尺寸和位置，这样有助于后面我们实现动态改变裁剪区域的实现。
缩放功能
这里实现缩放的原理实际是对放置图片的 UIImageView 的 frame 进行修改，首先我们要记录下最初的 UIImageView 的 frame
self.originalFrame = CGRectMake(self.cropAreaX - (tempWidth - self.cropAreaWidth)/2, self.cropAreaY - (tempHeight - self.cropAreaHeight)/2, tempWidth, tempHeight);
然后为 cropView 添加手势
// 捏合手势
UIPinchGestureRecognizer *pinGesture = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(handleCenterPinGesture:)];
[self.view addGestureRecognizer:pinGesture];
然后是手势处理函数
-(void)handleCenterPinGesture:(UIPinchGestureRecognizer *)pinGesture
{
CGFloat scaleRation = 3;
UIView * view = self.bigImageView;
// 缩放开始与缩放中
if (pinGesture.state == UIGestureRecognizerStateBegan || pinGesture.state == UIGestureRecognizerStateChanged) {
// 移动缩放中心到手指中心
CGPoint pinchCenter = [pinGesture locationInView:view.superview];
CGFloat distanceX = view.frame.origin.x - pinchCenter.x;
CGFloat distanceY = view.frame.origin.y - pinchCenter.y;
CGFloat scaledDistanceX = distanceX * pinGesture.scale;
CGFloat scaledDistanceY = distanceY * pinGesture.scale;
CGRect newFrame = CGRectMake(view.frame.origin.x + scaledDistanceX - distanceX, view.frame.origin.y + scaledDistanceY - distanceY, view.frame.size.width * pinGesture.scale, view.frame.size.height * pinGesture.scale);
view.frame = newFrame;
pinGesture.scale = 1;
}
// 缩放结束
if (pinGesture.state == UIGestureRecognizerStateEnded) {
CGFloat ration = view.frame.size.width / self.originalFrame.size.width;
// 缩放过大
if (ration > 5) {
CGRect newFrame = CGRectMake(0, 0, self.originalFrame.size.width * scaleRation, self.originalFrame.size.height * scaleRation);
view.frame = newFrame;
}
// 缩放过小
if (ration < 0.25) {
view.frame = self.originalFrame;
}
// 对图片进行位置修正
CGRect resetPosition = CGRectMake(view.frame.origin.x, view.frame.origin.y, view.frame.size.width, view.frame.size.height);
if (resetPosition.origin.x >= self.cropAreaX) {
resetPosition.origin.x = self.cropAreaX;
}
if (resetPosition.origin.y >= self.cropAreaY) {
resetPosition.origin.y = self.cropAreaY;
}
if (resetPosition.size.width + resetPosition.origin.x < self.cropAreaX + self.cropAreaWidth) {
CGFloat movedLeftX = fabs(resetPosition.size.width + resetPosition.origin.x - (self.cropAreaX + self.cropAreaWidth));
resetPosition.origin.x += movedLeftX;
}
if (resetPosition.size.height + resetPosition.origin.y < self.cropAreaY + self.cropAreaHeight) {
CGFloat moveUpY = fabs(resetPosition.size.height + resetPosition.origin.y - (self.cropAreaY + self.cropAreaHeight));
resetPosition.origin.y += moveUpY;
}
view.frame = resetPosition;
// 对图片缩放进行比例修正，防止过小
if (self.cropAreaX < self.bigImageView.frame.origin.x
|| ((self.cropAreaX + self.cropAreaWidth) > self.bigImageView.frame.origin.x + self.bigImageView.frame.size.width)
|| self.cropAreaY < self.bigImageView.frame.origin.y
|| ((self.cropAreaY + self.cropAreaHeight) > self.bigImageView.frame.origin.y + self.bigImageView.frame.size.height)) {
view.frame = self.originalFrame;
}
}
}
