ios - 在 UIView 上涂鸦 - ios 开发

Question

你好，我正在做这个项目，允许用户在 UIView 上涂鸦。我的方法是创建 CGMutablePathRef 路径并在 TouchMoved 时向其添加新行。

相关代码如下，在UIView类中。

static CGMutablePathRef path; //create it as static value. 
//I got this habit from java coding but actually not sure 
//if it's a good way to do it in objective-c.


//draw the path

-(void)drawRect:(CGRect)rect{
    CGContextRef context = UIGraphicsGetCurrentContext(); 
    CGContextBeginPath(context);
    CGContextAddPath(context, path);
    CGContextStrokePath(context);
    CGPathRelease(path);
}

//touch began. create the path and add point.
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{

    path = CGPathCreateMutable();
    UITouch *touch = [touches anyObject];
    CGPoint point = [touch locationInView:self];
    CGPathMoveToPoint(path, NULL, point.x, point.y);
    [self setNeedsDisplay];            
}


//add points when touch moved
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{

    UITouch *touch = [touches anyObject];
    CGPoint point = [touch locationInView:self];

    CGPathAddLineToPoint(path, NULL, point.x, point.y);
    [self setNeedsDisplay];

}

//last points when touch ends
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    CGPoint point = [touch locationInView:self];
    CGPathAddLineToPoint(path, NULL, point.x, point.y);
    [self setNeedsDisplay];
}

但是，我遇到了错误，而且我并没有真正理解它们……我猜这是 UIGestureRecognizer 的问题，我从其他涂鸦代码中看到了这一点。是不是需要给它加上 UIGestureRecognizer 呢？我还没有学到任何关于它的东西，所以我试图避免使用它。但如果这是必须的，我会试一试。

我想到的另一种方法是将所有点位置存储到一个可变数组中，因为我必须将这些点位置值存储在某个地方。但是，我不知道数组是否合适，因为我还没有找到将浮点值存储到数组的方法。如果有人可以帮助我，那将非常有帮助。谢谢!

Answer 1

感谢那些向我提供帮助的人。在查看了一堆代码和方法之后，幸运的是我找到了解决这个问题的有效方法!

一般我的SketchView中的imageView是在我画图的时候动态更新的。也就是说，每次我画更多的像素时，都会在新的像素上添加一条线，更改 UIImageView，然后将其设置为 UIView 的背景图像。

SketchView.h

@property (assign, nonatomic) CGPoint CurrentPoint;
@property (assign, nonatomic) CGPoint PreviousPoint;
@property (assign, nonatomic) CGPoint InitialPoint;

SketchView.m

@synthesize CurrentPoint;
@synthesize PreviousPoint;
@synthesize InitialPoint;


//begin the touch. store the initial point because I want to connect it to the last   
//touch point
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    CGPoint point = [touch locationInView:image];
    InitialPoint = point;

    }


//When touch is moving, draw the image dynamically
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{

UITouch *touch = [touches anyObject];
PreviousPoint = [touch previousLocationInView:image];
CurrentPoint = [touch locationInView:image];
UIGraphicsBeginImageContext(image.frame.size); 
CGContextRef ctx = UIGraphicsGetCurrentContext();   
[image.image drawInRect:CGRectMake(0, 0, image.frame.size.width,   image.frame.size.height)];
CGContextSetLineCap(ctx, kCGLineCapRound);
CGContextSetLineWidth(ctx, 5.0);
CGContextSetRGBStrokeColor(ctx, 1.0, 0.0, 0.0, 1.0);
CGContextBeginPath(ctx);
CGContextMoveToPoint(ctx, PreviousPoint.x, PreviousPoint.y);
CGContextAddLineToPoint(ctx, CurrentPoint.x, CurrentPoint.y);
CGContextStrokePath(ctx);
image.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}



- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{

UITouch *touch = [touches anyObject];
PreviousPoint = [touch previousLocationInView:image];
CurrentPoint = [touch locationInView:image];
UIGraphicsBeginImageContext(image.frame.size); 
CGContextRef ctx = UIGraphicsGetCurrentContext();
[image.image drawInRect:CGRectMake(0, 0, image.frame.size.width, image.frame.size.height)];
CGContextSetLineCap(ctx, kCGLineCapRound);
CGContextSetLineWidth(ctx, 5.0);
CGContextSetRGBStrokeColor(ctx, 1.0, 0.0, 0.0, 1.0);
CGContextBeginPath(ctx);
CGContextMoveToPoint(ctx, PreviousPoint.x, PreviousPoint.y);
CGContextAddLineToPoint(ctx, CurrentPoint.x, CurrentPoint.y);

//I connected the last point to initial point to make a closed region
CGContextMoveToPoint(ctx, CurrentPoint.x, CurrentPoint.y);
CGContextAddLineToPoint(ctx, InitialPoint.x, InitialPoint.y);
CGContextStrokePath(ctx);
image.image = UIGraphicsGetImageFromCurrentImageContext();


UIGraphicsEndImageContext();
}

而且有效!

附注我找到了

 PreviousPoint = [touch previousLocationInView:image];

非常有帮助，虽然在我发现的涂鸦代码中没有提到太多......我希望这会有所帮助。 :)