Question

我正在按照教程创建一个简单的绘图板应用程序（http://www.raywenderlich.com/18840/how-to-make-a-simple-drawing-app-with-uikit#comments）

该应用程序中有一个UIViewController和一个UIImageView。在实现了touchBegin，touchMoved和touchEnd之后，我可以绘制但是在每个笔画结束后，整个画面都会向上移动。因此，经过几次笔画后，整个画面将被扭曲并挤压到屏幕的最顶端。有什么建议？非常感谢你。

以下是代码：

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    self.mouseSwiped = NO;
    UITouch *touch = [touches anyObject];
    self.lastPoint =[touch locationInView:self.view];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    self.mouseSwiped = YES;
    //find out the position where the touch event happened
    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self.view];

    //Setup the drawing context and prepare to draw something
    UIGraphicsBeginImageContext(self.view.frame.size);

    //Create a drawing area that is of the same size as the view dimensions
    [self.mainImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];

    //Set the drawing starting point
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), self.lastPoint.x, self.lastPoint.y);

    //Setup a line from the starting point to specified point, i.e current point in this case
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);

    //Set the drawing style
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), self.brush);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), self.red, self.green, self.blue, 1);
    CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeNormal);


    //Paint the line
    CGContextStrokePath(UIGraphicsGetCurrentContext());

    self.mainImage.image=UIGraphicsGetImageFromCurrentImageContext();
    [self.mainImage setAlpha:self.opacity];
    UIGraphicsEndImageContext();

    self.lastPoint = currentPoint;
}

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

    if(!self.mouseSwiped){
        UIGraphicsBeginImageContext(self.view.frame.size);
        [self.mainImage.image drawInRect:
         CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), self.brush);
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(),
                                   self.red, self.green, self.blue, self.opacity);
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), self.lastPoint.x, self.lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), self.lastPoint.x, self.lastPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        CGContextFlush(UIGraphicsGetCurrentContext());
        self.mainImage.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:self.opacity];
    self.mainImage.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
}

Answer 1

您正在使用的2个视图的大小可能不匹配，因此当您在2个不同的坐标空间之间移动时，您将获得缩放效果。

每次描边后，UIImageView中的绘图都会向上移动

1 个答案: