手势识别器重置

Question

我在按钮上添加了平移手势，当我在不添加任何其他代码的情况下移动它时，一切都很好，但是当我添加一些代码时（在下面的示例中进行了注释），按钮开始重置为其原点位置。

为什么会这样呢？ 这是什么原因？

- (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

您在UIGestureRecognizerStateChanged情况下添加的代码，将其移至Action方法的标题中：

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];

之后，您要做的另一件事是在Switch方法中创建另一个Case：

//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];
}

因此，我在UIGestureRecognizerStateEnded状态下所做的就是，我到达了用户发送图像的最后一个点。 在那之后，我将图像的中心设置为等于图像是最后一刻的点。 因此，现在图像将不会返回到上一个点，但它将保留在用户将要拍摄的位置。