NSUndoManager使用旋轉手勢撤消UIImage旋轉

Question

如何使用NSUndoManager旋轉UIImageView使用旋轉手勢？這是我的代碼輪換。

- (void)handleRotate:(UIRotationGestureRecognizer *)recognizer 
{ 
    if (recognizer.state == UIGestureRecognizerStateBegan) { 
     prevRotation = 0.0; 
    } 

    float thisRotate = recognizer.rotation - prevRotation; 
    prevRotation = recognizer.rotation; 
    recognizer.view.transform = CGAffineTransformRotate(recognizer.view.transform, thisRotate); 

    CGPoint lastpoint = point; 
} 

Answer 1

首先，請閱讀「Using Undo on iPhone」。確保你已經在你的響應者鏈中設置了undoManager屬性（可能在你的視圖控制器中）。

我們只想在手勢結束時推送撤消操作。但是當我們推動撤消動作時，我們需要知道手勢開始時視圖的變換。創建一個實例變量來保存原來的變換：

@implementation YourViewController { 
    CGAffineTransform _originalImageViewTransform; 
} 

接下來，我們需要推動的撤消操作和設置方法視圖的轉換：

- (void)setTransform:(CGAffineTransform)newTransform ofView:(UIView *)view 
    undoTransform:(CGAffineTransform)undoTransform 
{ 
    // If I'm called because the gesture ended, this pushes an undo action. 
    // If I'm called because the user requested an undo, this pushes a redo action. 
    [[self.undoManager prepareWithInvocationTarget:self] 
     setTransform:undoTransform ofView:view undoTransform:newTransform]; 

    // Now actually set the transform. 
    view.transform = newTransform; 
} 

你handleRotate:方法需要檢測的狀態手勢並採取適當的行動。

- (void)handleRotate:(UIRotationGestureRecognizer *)recognizer { 
    UIView *view = recognizer.view; 
    UIGestureRecognizerState state = recognizer.state; 

    if (state == UIGestureRecognizerStateCancelled) { 
     view.transform = _originalImageViewTransform; 
     return; 
    } 

    if (state == UIGestureRecognizerStateBegan) { 
     _originalImageViewTransform = view.transform; 
    } 

    CGAffineTransform transform = view.transform; 
    transform = CGAffineTransformRotate(transform, recognizer.rotation); 
    recognizer.rotation = 0; // This line means we don't need prevRotation 

    if (state == UIGestureRecognizerStateEnded) { 
     [[ The gesture ended, so push an undo action before setting the transform. 
     [self setTransform:transform ofView:view undoTransform:_originalImageViewTransform]; 
    } else { 
     // The gesture changed but didn't end, so don't push an undo action. 
     view.transform = transform; 
    } 
}