Disabling Pan Gesture if out of bounds detected

问题:

I have a UIView I am trying to move up and down the screen, however I only wish to enable it to pan so that you cannot drag the view down when it is in its normal position (0, 0)

I tried to detect when the recognizer's center is not half the height of the view, however the view is then immovable, and the center is always half the height (230 in this case).

Any ideas?

- (IBAction)panDetected:(UIPanGestureRecognizer *)recognizer {
    CGPoint translation = [recognizer translationInView:self.view];
    NSLog(@"\ncenter.y: %f\ntranslation.y: %f\n", recognizer.view.center.y, translation.y);
    if (recognizer.view.center.y > ([[UIScreen mainScreen] bounds].size.height - 20)/2) {
            return;
    }
    recognizer.view.center = CGPointMake(recognizer.view.center.x,
                                         recognizer.view.center.y + translation.y);
    [recognizer setTranslation:CGPointMake(0, 0) inView:self.view];
}

回答1:

Instead of manually computing whether the points are within the view's bounds, use CGRectContainsPoint(rect, point). This is what works for me, and I like it because it's shorter and more readable:

func handlePan(pan: UIPanGestureRecognizer) {
    switch pan.state {
    case .Began:
        if CGRectContainsPoint(self.pannableView.frame, pan.locationInView(self.pannableView)) {
            // Gesture started inside the pannable view. Do your thing.
        }
}

回答2:

CGPoint translation = [recognizer translationInView:self.view];
CGPoint finalpoint = CGPointMake(recognizer.view.center.x + translation.x, recognizer.view.center.y+ translation.y);

//limit the boundary    
if ((recognizer.view.frame.origin.x>0 && translation.x > 0) || (recognizer.view.frame.origin.x + recognizer.view.frame.size.width<=320 && translation.x < 0))
    finalpoint.x = recognizer.view.center.x;

if ((recognizer.view.frame.origin.y>0 && translation.y > 0) || (recognizer.view.frame.origin.y + recognizer.view.frame.size.height<=self.view.frame.size.height && translation.y < 0))
    finalpoint.y = recognizer.view.center.y;

//set final position
recognizer.view.center = finalpoint;
[recognizer setTranslation:CGPointZero inView:self.view];

回答3:

try

CGPoint translation = [recognizer translationInView:self.view];  
if (translation.x+recognizer.view.frame.origin.x<0||translation.y+recognizer.view.frame.origin.y<0)
    {
        return;
    }

 recognizer.view.center = CGPointMake(recognizer.view.center.x,
                                     recognizer.view.center.y + translation.y);
[recognizer setTranslation:CGPointMake(0, 0) inView:self.view];

回答4:

recognizer.view.center = CGPointMake(recognizer.view.center.x, MAX(recognizer.view.center.y + translation.y, ([[UIScreen mainScreen] bounds].size.height - 20)/2));