NSUndoManager 使用旋转手势撤消 UIImage 旋转

Question

如何使用NSUndoManager 使用旋转手势来旋转UIImageView？这是我的轮换代码。

- (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，阅读“Using Undo on iPhone”。确保您已在响应者链中的某处（可能在您的视图控制器中）设置了 undoManager 属性。

我们只想在手势结束时推送撤消操作。但是当我们推送撤消动作时，我们需要知道手势开始时视图的变换。创建一个实例变量来保存原始转换：

@implementation YourViewController {
    CGAffineTransform _originalImageViewTransform;
}

接下来，我们需要一个方法来推送撤消操作并设置视图的变换：

- (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;
}

您的handleRotate: 方法需要检测手势的状态并采取适当的操作。

- (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;
    }
}