UIPinchGestureRecognizer向内捏“慢”

Question

我在我的应用程序中使用UIPinchGestureRecognizer来放大视图(是的，我不使用UIScrollView是有原因的)。当我用手指向外捏的时候，视图会像预期的那样放大，如果我在没有把手指从屏幕上拿下来的情况下倒转，它也会放大。但是，如果我通过向内收缩来启动缩放，视图缩放的速度会大大减慢。我猜这是因为UIPinchGestureRecognizer是如何工作的--当向外收缩时，UIPinchGestureRecognizer的规模大于1，而向内收缩时则小于1。不幸的是，我不知道如何在代码中准确地反映这一点。

- (IBAction)didDetectPinchGesture:(id)sender {
    UIPinchGestureRecognizer *gestureRecognizer = (UIPinchGestureRecognizer *)sender;

    CGFloat scale = [gestureRecognizer scale];

    switch ([gestureRecognizer state]) {
        case UIGestureRecognizerStateBegan:
            _lastScale = [gestureRecognizer scale];
            break;

        case UIGestureRecognizerStateChanged:

            CGFloat currentScale = [[self.imageView.layer valueForKeyPath:@"transform.scale"] floatValue];

            // Constants to adjust the max/min values of zoom
            const CGFloat kMaxScale = 5.0;
            const CGFloat kMinScale = 1.0;

            CGFloat newScale = 1 -  (_lastScale - scale); // new scale is in the range (0-1)
            newScale = MIN(newScale, kMaxScale / currentScale);
            newScale = MAX(newScale, kMinScale / currentScale);

            NSLog(@"%f", newScale);

            CGAffineTransform transform = CGAffineTransformScale([self.imageView transform], newScale, newScale);
            self.imageView.transform = transform;

            _lastScale = scale;  // Store the previous scale factor for the next pinch gesture call
            break;

        default:
            _lastScale = [gestureRecognizer scale];
            break;
    }
}

Answer 1

对此，一个非常简单的解决方案是，在您完成之后将gestureRecognizer scale重置为1：

    ...
    default:
        _lastScale = [gestureRecognizer scale];
        // Add this:
        [gestureRecognizer setScale:1];
        break;
    }