iphone - 如何在iphone的车速表中旋转图像

Question

以下是在触摸事件上旋转箭头（uiimage）的代码。在这我减去两个触摸的位置之前和当前但问题是箭头（uiimage）有时会在触摸的相反方向上移动。

- (void) touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event
{
    UITouch *touch = [touches anyObject];        
    NSLog(@"%@",[touch view]);   
    if ([touch view] == ImgViewArrowImage) 
    {
    CGPoint currentLocation = [touch locationInView:touch.view];
    CGPoint pastLocation = [touch previousLocationInView:touch.view];

    CGPoint d1 = CGPointMake(currentLocation.x-touch.view.center.x, currentLocation.y-touch.view.center.y);   
    CGPoint d2 = CGPointMake(pastLocation.x-touch.view.center.x, pastLocation.y-touch.view.center.y);

    CGFloat angle1 = atan2(d1.y, d1.x); 
    CGFloat angle2 = atan2(d2.y, d2.x); 
    [[ImgViewArrowImage layer] setAnchorPoint:CGPointMake(0.0, 0.5)];
    [[ImgViewArrowImage layer] setPosition:CGPointMake(159,211)];

    ImgViewArrowImage.transform = CGAffineTransformRotate(ImgViewArrowImage.transform, angle1-angle2);
  } 
}

Answer 1

我只是从我的代码中删除了 2 行，我的代码现在正在运行，所以最终的代码是

- (void) touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event
{
    UITouch *touch = [touches anyObject];        
    NSLog(@"%@",[touch view]);   
    if ([touch view] == ImgViewArrowImage) 
    {
    CGPoint d1 = [touch locationInView:touch.view];
    CGPoint d2 = [touch previousLocationInView:touch.view];


    CGFloat angle1 = atan2(d1.y, d1.x); 
    CGFloat angle2 = atan2(d2.y, d2.x); 
    [[ImgViewArrowImage layer] setAnchorPoint:CGPointMake(0.0, 0.5)];
    [[ImgViewArrowImage layer] setPosition:CGPointMake(159,211)];

    ImgViewArrowImage.transform = CGAffineTransformRotate(ImgViewArrowImage.transform, angle1-angle2);
  } 
}

Answer 2

根据原始问题的评论，保持角度高于 0：

float _angle = angle1 - angle2;
if (_angle < 0) _angle += M_PI; // if you are working with radians, otherwise: _angle += 360.f;

还有另一个原因：

我们都知道它是如何工作的：分母为零atan(...)时是不确定的，因为除以零是一个未定义的情况，理论上的结果是无限的，但在这种情况下你可能会得到值。atan(...)floatMAX_FLOAT

Answer 3

使用此代码：

 self.button.layer.anchorPoint = CGPointMake(self.button.layer.anchorPoint.x, self.button.layer.anchorPoint.y*2);

[UIView beginAnimations:nil context:nil];
[UIView setAnimationDuration:0.5f];
[self.button setTransform: CGAffineTransformMakeRotation((M_PI / 180) * -40.0579987)];
[UIView commitAnimations];