ios - 如何撤消线条描边 ios

Question

我正在开发一个着色应用程序，但是我无法实现一个 UNDO 按钮。我不确定该方法，我已尝试实现 NSUndoManager，但我无法使其有效工作。我的方法可能不正确。根据我的示例，我将非常感谢使用代码的答案。

- (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();
}

已经有人问过类似的问题，但没有给出明确的答案，还有一些没有得到回答。

* 根据 gabbler 回答编辑 1 *

#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 的父类(super class)UIResponder 有一个NSUndoManager 属性，可以在这里使用。上面的代码为 imageView 执行设置图像操作，要撤消该操作，您必须保留对之前设置到 imageView 的图像的引用。你可以创建一个名为 previousImage 的实例变量，在 viewDidLoad 中设置

previousImage = self.tempImage.image;

这里是为 UIImageView 设置图像的函数。

- (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 中。

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

当您单击撤消按钮时。

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

编辑

上述方法会造成内存问题，不要在undoManager中保存图片，而是保存线路径点，这里是一个sample project具有 undo 和 redo 功能。