沿着滑动路径用箭头在滑动手指上画线

Question

我正在创建一个应用程序，当我在屏幕上滑动手指时，我正在使用代码画线。

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(),3.0);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0.0, 0.5, 0.6, 1.0);
    CGContextBeginPath(UIGraphicsGetCurrentContext());
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), startPoint.x, startPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), endPoint.x, endPoint.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());
}

我也在使用代码同时在该行移动箭头....

-(void)moveBallConstantly
{
 [UIView animateWithDuration:0.01f animations: ^{
         [appDel.ballImageView setCenter:CGPointMake(appDel.ballImageView.center.x +        (x/increamentFraction), appDel.ballImageView.center.y + (y/increamentFraction))];
   }];
}

它只是功能的一小部分。我可以不断移动箭头，但为了更好地平滑箭头移动，我使用计时器 .01 重复调用此函数。

由于我同时进行这两项处理，因此有时会产生问题。有时箭头移动方法会延迟，有时线条绘制方法会延迟。

Answer 1

我会报废计时器并将其移至touchesMoved。

我的解决方案可让您在 UIImageView 画布上绘图，并在您绘图时让一个白框跟随您的手指。将其放入任何 UIView 中进行试用：

// These should probably be @properties
static CGPoint lastPoint;
static CGPoint currentPoint;
static UIView *box;
static UIImageView *canvas;

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch  = [touches anyObject];
    currentPoint    = [touch locationInView:self];
    lastPoint       = [touch locationInView:self];

    // Create the canvas the first time. Should probably do this elsewhere
    // but done here for paste-ability
    if (canvas == nil)
    {
        canvas = [[UIImageView alloc] initWithFrame:self.frame];
        canvas.backgroundColor = [UIColor redColor];
        [self addSubview:canvas];
    }

    // Create the box that follows the finger. Should probably do this elsewhere
    // but done here for paste-ability
    if (box == nil)
    {
        box = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 50, 50)];
        box.backgroundColor = [UIColor whiteColor];
        [self addSubview:box];
    }

    // Ensure we can see it and move it right away
    box.alpha = 1.0f;
    box.center = CGPointMake(currentPoint.x, currentPoint.y - 50);
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    currentPoint = [touch locationInView:self];

    // Set up everything for drawing
    UIGraphicsBeginImageContext(canvas.frame.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [canvas.image drawInRect:CGRectMake(0, 0, canvas.image.size.width, canvas.image.size.height)];
    CGContextSetLineCap(context, kCGLineCapRound);
    CGContextSetLineWidth(context, 1);
    CGContextSetStrokeColorWithColor (context, [UIColor blueColor].CGColor);

    // Draw the path
    CGContextBeginPath(context);
    CGContextMoveToPoint(context, lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(context, currentPoint.x, currentPoint.y);
    CGContextStrokePath(context);
    canvas.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    // Animate the box very quickly to the new location
    [UIView animateWithDuration:0.1f
                          delay:0
                        options:UIViewAnimationOptionCurveEaseInOut
                     animations:^{
                        box.center = CGPointMake(box.center.x + (currentPoint.x - lastPoint.x),
                                                 box.center.y + (currentPoint.y - lastPoint.y));
                     }
                     completion:nil];

    // Remember our last touch
    lastPoint = currentPoint;
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    // Finish it off by fading out the box
    [UIView animateWithDuration:0.4f animations:^{
        box.alpha = 0.0f;
    }];
}