拖放对象并将其返回到原始位置

Question

我试图拖动一个图像,让它在释放后返回原来的位置.到目前为止,我可以使用以下代码将其创建为按钮来拖动图像:(在此问题的答案中可以看到:iOS中的基本拖放)

UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
[button addTarget:self action:@selector(imageTouch:withEvent:) forControlEvents:UIControlEventTouchDown];
[button addTarget:self action:@selector(imageMoved:withEvent:) forControlEvents:UIControlEventTouchDragInside];
[button setImage:[UIImage imageNamed:@"vehicle.png"] forState:UIControlStateNormal];
[self.view addSubview:button];

后来我定义:

- (IBAction) imageMoved:(id) sender withEvent:(UIEvent *) event
{
    CGPoint point = [[[event allTouches] anyObject] locationInView:self.view];
    UIControl *control = sender;
    control.center = point;
}

如何在释放后将其恢复到原始位置？对于初学者我会保存每个图像应该返回的位置,但是,无论如何,无论如何都要指示UIImage从它的当前位置移动并移动到另一个？或任何其他替代解决方案？

Answer 1

Apple推荐UIGestureRecognizer用于最近的iOS.你不仅可以将它用于UIButton,还可以用于UIView(尤其是你的UIImageView)等等.所以我想推荐它.

在界面中:

@interface TestDragViewController : UIViewController {
    IBOutlet UIImageView *dragImage;
    CGPoint originalCenter;
}

在viewDidLoad中,plz记得启用userInteraction:

- (void)viewDidLoad {
    [super viewDidLoad];


    UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self 
                                                                                 action:@selector(dragGesture:)];
    [dragImage addGestureRecognizer:panGesture];
    [dragImage setUserInteractionEnabled:YES];
}

在它的选择器中,我只是设置动画来可视化返回的效果:

#pragma mark -
#pragma mark UIPanGestureRecognizer selector
- (void) dragGesture:(UIPanGestureRecognizer *) panGesture{
    CGPoint translation = [panGesture translationInView:self.view];

    switch (panGesture.state) {
        case UIGestureRecognizerStateBegan:{
            originalCenter = dragImage.center;
        }
            break;
        case UIGestureRecognizerStateChanged:{
            dragImage.center = CGPointMake(dragImage.center.x + translation.x,
                                           dragImage.center.y + translation.y);
        }
            break;
        case UIGestureRecognizerStateEnded:{            
            [UIView animateWithDuration:kImageReturnTime 
                             animations:^{
                                 dragImage.center = originalCenter;
                             }
                             completion:^(BOOL finished){
                                 NSLog(@"Returned");
                             }];
        }
            break;
        default:
            break;
    }

    [panGesture setTranslation:CGPointZero inView:self.view];
}

干杯,

汤米

Answer 2

你知道吗，我昨天刚刚在做这个，所以这里有一些额外的动画：

- (void)previewImageTouchUpInside:(UIButton*)aButton {
    if (!previewImageDragged) {
        [self selectPreviewImage:aButton];
        return;
}

    previewImageDragged = NO;

    // If user drag photo a little and then release, we'll still treat it as a tap
    //  instead of drag
    if ((originalPositionOfButton.x - aButton.center.x) * 
      (originalPositionOfButton.x - aButton.center.x) + 
      (originalPositionOfButton.y - aButton.center.y) * 
      (originalPositionOfButton.y - aButton.center.y) < 10) {
        aButton.center = originalPositionOfButton;
        [self selectPreviewImage:aButton];
        return;
    }

    [UIView animateWithDuration:0.5
        delay:0
        options:UIViewAnimationOptionCurveEaseOut |
        UIViewAnimationOptionAllowUserInteraction animations:^{
        aButton.center = originalPositionOfButton;
    } completion:nil];
}



- (void)previewImageDraggedInside:(UIButton*)aButton event:(UIEvent*)event {
    if (!previewImageDragged) {
        originalPositionOfButton = aButton.center;
        [self.view bringSubviewToFront:aButton];
        [self.view bringSubviewToFront:[self.view viewWithTag:CHOOSE_PHOTO_BUTTON_TAG]];
    }

    UITouch* touch = [[event allTouches] anyObject];

    previewImageDragged = YES;
    aButton.center = CGPointMake(aButton.center.x+[touch locationInView:self.view].x-
        [touch previousLocationInView:self.view].x, 
        aButton.center.y+[touch locationInView:self.view].y-
        [touch previousLocationInView:self.view].y);
}

它仍然有一些神奇的数字，我没有重命名函数和变量以适合您的示例，但它应该很清楚。我还在这里进行了缩进，因为我不会手动断开代码中的长行。