如何撤消一个行中的ios

我开发一个着色应用程序，但是我不能设法实现一个UNDObutton。 我不确定的方法，我尝试过实施NSUndoManager，但我无法得到有效的工作。 我的方法可能不正确。 林将不胜感激基于我的例子使用代码的答案。

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { mouseSwiped = NO; UITouch *touch = [touches anyObject]; lastPoint = [touch locationInView:self.view]; } - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { mouseSwiped = YES; UITouch *touch = [touches anyObject]; CGPoint currentPoint = [touch locationInView:self.view]; UIGraphicsBeginImageContext(self.view.frame.size); [self.tempImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)]; //get the current touch point and then draw a line with CGContextAddLineToPoint from lastPoint to currentPoint. You're right to think that this approach will produce a series of straight lines, but the lines are sufficiently short that the result looks like a nice smooth curve. CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y); CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y); //Now set our brush size and opacity and brush stroke color: CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound); CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush ); CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0); CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeNormal); //Finish it off by drawing the path: CGContextStrokePath(UIGraphicsGetCurrentContext()); self.tempImage.image = UIGraphicsGetImageFromCurrentImageContext(); [self.tempImage setAlpha:opacity]; UIGraphicsEndImageContext(); lastPoint = currentPoint; } - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event { /* check if mouse was swiped. If it was, then it means touchesMoved was called and you don't need to draw any further. However, if the mouse was not swiped, then it means user just tapped the screen to draw a single point. In that case, just draw a single point. */ if(!mouseSwiped) { UIGraphicsBeginImageContext(self.view.frame.size); [self.tempImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)]; CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound); CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush); CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, opacity); CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y); CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y); CGContextStrokePath(UIGraphicsGetCurrentContext()); CGContextFlush(UIGraphicsGetCurrentContext()); self.tempImage.image = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); } UIGraphicsBeginImageContext(self.mainImage.frame.size); [self.mainImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) blendMode:kCGBlendModeNormal alpha:1.0]; [self.tempImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) blendMode:kCGBlendModeNormal alpha:opacity]; //Once the brush stroke is done, merge the tempDrawImage with mainImage, self.mainImage.image = UIGraphicsGetImageFromCurrentImageContext(); self.tempImage.image = nil; UIGraphicsEndImageContext(); } 

也有类似的问题，但没有给出明确的答案，还有一些没有答案。

*编辑1基于gabbler答案*

 #import "ViewController.h" @interface ViewController () @property (weak, nonatomic) IBOutlet UIImageView *mainImage; @property (weak, nonatomic) IBOutlet UIImageView *tempImage; @property (weak, nonatomic) IBOutlet UIImageView *palette; @property (nonatomic) UIImage * previousImage; @property (nonatomic,readonly) NSUndoManager * undoManager; - (IBAction)colorPressed:(id)sender; - (IBAction)erase:(id)sender; - (IBAction)undo:(id)sender; @end @implementation ViewController //gabbler code - (void)setImage:(UIImage*)currentImage fromImage:(UIImage*)preImage { // Prepare undo-redo [[self.undoManager prepareWithInvocationTarget:self] setImage:preImage fromImage:currentImage]; self.mainImage.image = currentImage; self.tempImage.image = currentImage; self.previousImage = currentImage; } - (IBAction)trash:(id)sender { self.mainImage.image = nil; } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. red = 0.0/255.0; green = 0.0/255.0; blue = 0.0/255.0; brush = 10.0; opacity = 1.0; //gabbler code self.previousImage = self.tempImage.image; } - (IBAction)erase:(id)sender { //set it to background color red = 255.0/255.0; green = 255.0/255.0; blue = 255.0/255.0; opacity = 1.0; } //gabbler code - (IBAction)undo:(id)sender { [self.undoManager undo]; } #pragma mark - Touches - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { mouseSwiped = NO; UITouch *touch = [touches anyObject]; lastPoint = [touch locationInView:self.view]; } - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { mouseSwiped = YES; UITouch *touch = [touches anyObject]; CGPoint currentPoint = [touch locationInView:self.view]; UIGraphicsBeginImageContext(self.view.frame.size); [self.tempImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)]; //get the current touch point and then draw a line with CGContextAddLineToPoint from lastPoint to currentPoint. You're right to think that this approach will produce a series of straight lines, but the lines are sufficiently short that the result looks like a nice smooth curve. CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y); CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y); //Now set our brush size and opacity and brush stroke color: CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound); CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush ); CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0); CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeNormal); //Finish it off by drawing the path: CGContextStrokePath(UIGraphicsGetCurrentContext()); self.tempImage.image = UIGraphicsGetImageFromCurrentImageContext(); [self.tempImage setAlpha:opacity]; UIGraphicsEndImageContext(); lastPoint = currentPoint; } - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event { /* check if mouse was swiped. If it was, then it means touchesMoved was called and you don't need to draw any further. However, if the mouse was not swiped, then it means user just tapped the screen to draw a single point. In that case, just draw a single point. */ if(!mouseSwiped) { UIGraphicsBeginImageContext(self.view.frame.size); [self.tempImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)]; CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound); CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush); CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, opacity); CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y); CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y); CGContextStrokePath(UIGraphicsGetCurrentContext()); CGContextFlush(UIGraphicsGetCurrentContext()); self.tempImage.image = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); } UIGraphicsBeginImageContext(self.mainImage.frame.size); [self.mainImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) blendMode:kCGBlendModeNormal alpha:1.0]; [self.tempImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) blendMode:kCGBlendModeNormal alpha:opacity]; //Once the brush stroke is done, merge the tempDrawImage with mainImage, self.mainImage.image = UIGraphicsGetImageFromCurrentImageContext(); self.tempImage.image = nil; UIGraphicsEndImageContext(); //gabbler code UIImage *currentImage = UIGraphicsGetImageFromCurrentImageContext(); [self setImage:currentImage fromImage:currentImage]; } @end 

Answer 1

UIViewController的超类UIResponder有一个NSUndoManager属性，可以在这里使用。 上面的代码为imageView执行一个设置图像操作，为了撤消操作，必须保留对imageView设置的前一个图像的引用。 您可以在viewDidLoad中设置一个名为previousImage的实例variables

 previousImage = self.tempImage.image; 

这里是为UIImageView设置图像的function。

 - (void)setImage:(UIImage*)currentImage fromImage:(UIImage*)preImage { // Prepare undo-redo [[self.undoManager prepareWithInvocationTarget:self] setImage:preImage fromImage:currentImage]; self.mainImage.image = currentImage; self.tempImage.image = currentImage; previousImage = currentImage; } 

在touchesEnded 。

 UIImage *currentImage = UIGraphicsGetImageFromCurrentImageContext(); [self setImage:currentImage fromImage:previousImage]; 

当你点击一个button来撤消。

 - (IBAction)btnClicked:(id)sender { [self.undoManager undo]; } 

编辑

上面的方法会导致内存问题，不保存图像在undoManager ，而是保存行path点，这里是一个具有undo和redofunction的示例项目 。