Question

我画了一条直线，我想以这样的方式制作它：当触摸移动很小（例如10像素）时，起点（fromPoint）将跟随触摸而不是保持第一次触摸。

- (void)drawRect:(CGRect)rect {

    CGPoint fromPoint;
    CGPoint toPoint;

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetLineWidth(context, 2.0);
    CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
    CGFloat components[] = {0.0, 0.0, 1.0, 1.0};
    CGColorRef color = CGColorCreate(colorspace, components);
    CGContextSetStrokeColorWithColor(context, color);
    CGContextSetLineCap(context, kCGLineCapRound);

    CGContextMoveToPoint(context, fromPoint.x, fromPoint.y);
    CGContextAddLineToPoint(context, toPoint.x, toPoint.y);
    CGContextStrokePath(context);

    CGColorSpaceRelease(colorspace);
    CGColorRelease(color);

}


//touch event
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch* touch = [touches anyObject];
    fromPoint = [touch locationInView:self];
    toPoint = [touch locationInView:self];

    [self setNeedsDisplay];
}

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

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

    // ***** not working ******
    // when touch movement is small (e.g 10 pixel), the starting point will follow the touch rather than staying at the first touch 
    if (fabs(_draw.toPoint.x - _draw.fromPoint.x) < 10 && fabs(_draw.toPoint.y - _draw.fromPoint.x) < 10){

    UITouch* touch = [touches anyObject];
    fromPoint = [touch locationInView:self];
    toPoint = [touch locationInView:self];

    };

    //************************//

    [self setNeedsDisplay];  

}


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

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

    [self setNeedsDisplay];

}

更新：目的是在实施放大镜时稍微调整起点。

Answer 1

它不起作用，因为除非你快速移动手指，否则你无法区分小动作和大动作。

您可以尝试在touchesBegan中启动计时器，并使用它来计算移动速度，从中可以在慢速和快速触摸之间设置一些参数。

你甚至可以使用UIPanGestureRecognizer来为你计算速度。

移动一条线的起点

1 个答案: