限制UIPinchGestureRecognizer缩放级别目标C斯威夫特3.0

Question

iOS的10.2雨燕3.0

试图这段代码从保罗·绍尔特博客翻译。由SO海报修正，更新代码！

http://paulsolt.com/blog/2011/03/limiting-uipinchgesturerecognizer-zoom-levels

示例代码

- (void)handlePinchGesture:(UIPinchGestureRecognizer *)gestureRecognizer { 

if([gestureRecognizer state] == UIGestureRecognizerStateBegan) { 
// Reset the last scale, necessary if there are multiple objects with different scales 
lastScale = [gestureRecognizer scale]; 
} 

if ([gestureRecognizer state] == UIGestureRecognizerStateBegan || 
[gestureRecognizer state] == UIGestureRecognizerStateChanged) { 

CGFloat currentScale = [[[gestureRecognizer view].layer  valueForKeyPath:@"transform.scale"] floatValue]; 

// Constants to adjust the max/min values of zoom 
const CGFloat kMaxScale = 2.0; 
const CGFloat kMinScale = 1.0; 

CGFloat newScale = 1 - (lastScale - [gestureRecognizer scale]); // new  scale is in the range (0-1) 
newScale = MIN(newScale, kMaxScale/currentScale); 
newScale = MAX(newScale, kMinScale/currentScale); 
CGAffineTransform transform = CGAffineTransformScale([[gestureRecognizer view] transform], newScale, newScale); 
[gestureRecognizer view].transform = transform; 

lastScale = [gestureRecognizer scale]; // Store the previous scale factor  for the next pinch gesture call 
} 
} 

差不多完成了，但似乎无法在这里找到用于雨燕3.0 CATransform关键的参考。我的代码...

if sender.state == .began { 
     // Reset the last scale, necessary if there are multiple objects with different scales 
     lastScale = sender.scale 
    } 

    if sender.state == .began || sender.state == .changed { 

     // UPDATED 
     currentScaleX = self.image2P.transform.scaleX 
     currentScaleY = self.image2P.transform.scaleY 


     self.image2P.transform = self.image2P.transform.scaledBy(x: 1.1, y: 1.1) 


     // Constants to adjust the max/min values of zoom 
     let kMaxScale:CGFloat = 2.0; 
     let kMinScale:CGFloat = 1.0; 

     var newScale = 1 - (lastScale - sender.scale) // new scale is in the range (0-1) 
     newScale = min(newScale, kMaxScale/currentScaleX) 
     newScale = max(newScale, kMinScale/currentScaleY) 
     self.image2P.transform = self.image2P.transform.scaledBy(x: newScale, y: newScale) 

     lastScale = sender.scale // Store the previous scale factor for the next pinch gesture call 
    } 

Answer 1

，可以储存xScale和yScale分开，因为一般来说也不能保证他们是平等的。

extension CGAffineTransform { 
    var scaleX: CGFloat { 
     return (a > 0 ? 1 : -1) * sqrt (a*a + c*c) 
    } 

    var scaleY: CGFloat { 
     return (d > 0 ? 1 : -1) * sqrt (b*b + d*d) 
    } 
} 

这些扩展方法，将工作返回正确的比例因子，即使您的观点也旋转和/或翻译：

view.transform = CGAffineTransform(scaleX: 1.5, y: 1.2).rotated(by: .pi/3.0).translatedBy(x: 50, y: 30) 
print("scaleX = \(view.transform.scaleX), scaleY = \(view.transform.scaleY)") 

输出：

的scaleX = 1.5 ，scaleY = 1.2

它可能并不明显，但a,b,c和d属性是transform矩阵的元素。您可以在Quartz 2D Programming Guide中找到更多详细信息。你也可以找到数学的详细信息here。请注意，b和c元素名称在这两个来源中交换。