我只想沿着y轴拖动dropTarget视图，并且只在特定的范围内拖动。

Question

if ([touch view]==dropTarget1)
{
  CGPoint current = [touch locationInView:self.view];
  if (homeY > 540 && homeY < dropTarget1.frame.origin.y+dropTarget1.frame.size.height)
  {
     dif = current.y - beginY;
     CGRect newDragObjectFrame = CGRectMake(self.dropTarget1.frame.origin.x, homeY+dif,
     self.dropTarget1.frame.size.width,dropTarget1.frame.size.height);
     self.dropTarget1.frame = newDragObjectFrame;
     homeY = homeY+dif;
  }
}

当我使用这段代码时，它是向上移动的，但我不能再上下移动它了。

Answer 1

您所遇到的问题可能是由于if语句中的情况所致。一旦homeY大于540或小于dropTarget1.frame.origin.y+dropTarget1.frame.size.height，条件将不再为真(除非在代码的其他地方更改homeY )，并且将忽略触摸。我认为获得您想要的交互的最好方法是使用UIPanGestureRecognizer。下面是一个如何做到这一点的例子：

// Add this to where you initialize dropTarget1
UIPanGestureRecognizer * panGesture = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(handlePan:)];
panGesture.delegate = self;
[dropTarget1 addGestureRecognizer:panGesture];


- (void)handlePan:(UIPanGestureRecognizer *)recognizer 
{
    CGPoint translation = [recognizer translationInView:self.dropTarget1];
    if (recognizer.view.center.y + translation.y > 80 && recognizer.view.center.y + translation.y < 350)
    {
        recognizer.view.center = CGPointMake(recognizer.view.center.x,recognizer.view.center.y + translation.y);
        [recognizer setTranslation:CGPointMake(0, 0) inView:self.dropTarget1];
    }
}

只需将80和350更改为实际需要的值。此外，您还需要将UIGestureRecognizerDelegate添加到类中。

祝好运!