如何在用户手指移动后绘制线条

Question

代码：

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();
    UIColor *grayColor = [UIColor colorWithRed: 0.8980392157 green: 0.8980392157 blue: 0.8980392157 alpha: 1.0];
    [grayColor set];
    CGContextSetLineWidth(context, 2.0);
    CGContextStrokeEllipseInRect(context, CGRectMake(100, 190, 101, 101));
}

我确实画了一个圆圈。当用户在上面移动手指时，我想在上面划一条线。我在谷歌上搜索了很多。但我找不到任何解决办法。任何帮助都将不胜感激。提前感谢。

Answer 1

您应该研究以下内容：

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event

这些是用于跟踪CCD_ 1的触摸的方法。

Answer 2

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
        UITouch *touch = [touches anyObject];
        CGPoint tapLocation = [touch locationInView:self.superDrawingLayer];  
        lastPoint = tapLocation;
}
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
        UITouch *touch = [touches anyObject];
        CGPoint tapLocation = [touch locationInView:self.superDrawingLayer];
        currentPoint = tapLocation;
        UIGraphicsBeginImageContext(self.superDrawingLayer.frame.size);
        [self.superDrawingLayer.image drawInRect:CGRectMake(0, 0, self.superDrawingLayer.frame.size.width, self.superDrawingLayer.frame.size.height)];
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), drwaingWidth);
        CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeColor);
        CGContextSetStrokeColorWithColor(UIGraphicsGetCurrentContext(), [[UIColor colorWithRed:1.0f green:0.764705f blue:0 alpha:1.0] CGColor]);
        CGContextBeginPath(UIGraphicsGetCurrentContext());
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        CGContextFlush(UIGraphicsGetCurrentContext());

        self.superDrawingLayer.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        lastPoint = tapLocation;
}
-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{
}

//这里superDrawingLayer是将在其上绘制线条的ImageView。