手势识别器重置

Question

I've added a pan gesture to my button, when i move it without any additional code, everything is well, but when i add some piece of code, which is commented in the example below, button starts reseting to its origin position.

Why is this happening? What's the reason for this?

- (IBAction)handlePan:(UIPanGestureRecognizer *)recognizer {
switch([recognizer state]){
    case  UIGestureRecognizerStateBegan: {
        UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        [button setFrame:recognizer.view.frame];
        [button setBackgroundColor: [UIColor redColor]];

//      [self.view insertSubview:button belowSubview:recognizer.view];
        _tempButton = button;

    }break;
    case  UIGestureRecognizerStateChanged: {

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

    }break;
}
}

Answer 1

The code that you have added at the UIGestureRecognizerStateChanged case, move it in the header of your Action Method:

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

After that another thing for you to do is to make another Case in your Switch Method:

//This checks if you ended the pan gesture (removed finger from object)
case  UIGestureRecognizerStateEnded:
{
    CGPoint velocity = [recognizer velocityInView:self.view];
    CGFloat magnitude = sqrtf((velocity.x * velocity.x) + (velocity.y * velocity.y));
    CGFloat slideMult = magnitude / 200;
    NSLog(@"magnitude: %f, slideMult: %f", magnitude, slideMult);

    float slideFactor = 0.1 * slideMult; // Increase for more of a slide
    CGPoint finalPoint = CGPointMake(recognizer.view.center.x + (velocity.x * slideFactor), 
                                 recognizer.view.center.y + (velocity.y * slideFactor));
    finalPoint.x = MIN(MAX(finalPoint.x, 0), self.view.bounds.size.width);
    finalPoint.y = MIN(MAX(finalPoint.y, 0), self.view.bounds.size.height);

    [UIView animateWithDuration:slideFactor*2 delay:0 options:UIViewAnimationOptionCurveEaseOut     animations:^{
    recognizer.view.center = finalPoint;
    } completion:nil];
}

So what I did above in the UIGestureRecognizerStateEnded state is that, i took the final point where the user sent the image. After that, i set the center of the image equal to the point that the image was the last moment. So now the image wont return to the previous point but it will remain where the user will take it.