#iOS开发笔记#如何限制UIImageView放大缩小的比例

最新推荐文章于 2022-02-16 10:14:36 发布

Bryster

最新推荐文章于 2022-02-16 10:14:36 发布

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本文介绍如何通过代码实现对UIImageView的放大缩小手势操作，并限制其最大最小缩放比例。使用UIPinchGestureRecognizer来监听两指缩放手势，通过计算当前缩放比例与目标比例之间的关系，确保UIImageView不会缩放到设定的最大最小值之外。

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当一个UIImageView实现了手势操作并可以用两指实现放大缩小之后，如何能限制放大缩小的比例？

(另：如何实现UIImageView的手势操作？ --> iOS UIImageView实现拖动，放大/缩小，旋转)

来源：

http://stackoverflow.com/a/5446348/2177332

代码实现：

@property CGFloat lastScale;

- (void)pinchGestureDetected:(UIPinchGestureRecognizer *)recognizer
{
    
    UIGestureRecognizerState state = [recognizer state];

    if(state == UIGestureRecognizerStateBegan) {
        // Reset the last scale, necessary if there are multiple objects with different scales
        _lastScale = [recognizer scale];
    }
    
    if (state == UIGestureRecognizerStateBegan ||
        state == UIGestureRecognizerStateChanged) {
        
        CGFloat currentScale = [[[recognizer view].layer valueForKeyPath:@"transform.scale"] floatValue];
        
        // Constants to adjust the max/min values of zoom
        const CGFloat kMaxScale = 3.0;
        const CGFloat kMinScale = 1.0;
        
        CGFloat newScale = 1 -  (_lastScale - [recognizer scale]);
        newScale = MIN(newScale, kMaxScale / currentScale);
        newScale = MAX(newScale, kMinScale / currentScale);
        CGAffineTransform transform = CGAffineTransformScale([[recognizer view] transform], newScale, newScale);
        [recognizer view].transform = transform;
        _lastScale = [recognizer scale];  // Store the previous scale factor for the next pinch gesture call

    }
}

注：kMaxScale和kMinScale分别代表最大和最小的缩放比例。