Question

在我的应用中，我有这个代码来拖动一个对象

我设定了手势：

UILongPressGestureRecognizer *downwardGesture = [[UILongPressGestureRecognizer new] initWithTarget:self action:@selector(dragGestureChanged:)];
downwardGesture.minimumPressDuration = 0.2;
[grid_element addGestureRecognizer:downwardGesture];
for (UILongPressGestureRecognizer *gestureRecognizer in self.view.gestureRecognizers)
{
    [gestureRecognizer requireGestureRecognizerToFail:downwardGesture];
}

在我的方法中：

- (void) dragGestureChanged:(UILongPressGestureRecognizer*)gesture{

    UIImageView *imageToMove;
    CGPoint pointInSelfView;

    if (gesture.state == UIGestureRecognizerStateBegan)
    {
        dragging = TRUE;
        CGPoint location = [gesture locationInView:grid_element];
        NSIndexPath *selectedIndexPath = [grid_element indexPathForItemAtPoint:location];
        if (selectedIndexPath==nil) {
            dragging = FALSE;
            return;
        }

        indexToHide = selectedIndexPath.row;
        imageToMove = [[UIImageView alloc]initWithImage:[UIImage imageNamed:@"image_1.png"]];
        [self.view addSubview:imageToMove];
        pointInSelfView = [gesture locationInView:self.view];
        [imageToMove setCenter:pointInSelfView];


    }
    else if (gesture.state == UIGestureRecognizerStateChanged)
    {
        pointInSelfView = [gesture locationInView:self.view];
        [imageToMove setCenter:pointInSelfView];

    }
    else if (gesture.state == UIGestureRecognizerStateEnded     ||
             gesture.state == UIGestureRecognizerStateCancelled ||
             gesture.state == UIGestureRecognizerStateFailed)
    {
        dragging = FALSE;
    }
}

它在UIGestureRecognizerStateBegan中工作，然后imageToMove在self.view中添加到正确的位置，但imageToMove不会拖入UIGestureRecognizerStateChanged;我在NSLog中显示pointInSelfView UIGestureRecognizerStateChanged，并且更改正确;问题出在哪里？

修改

如果我使用imageToMove作为IBOutlet它工作正常，但我不明白其中的区别。

Answer 1

如果您使用的是ARC，则iOS系统会释放对象 - imageToMove 使用retain属性创建属性会使系统保留对象，从而使其移动。

我唯一感到困惑的是[imageToMove setCenter:pointInSelfView];中没有错误的原因。应该有一个错误说 - 消息被发送到解除分配的实例。但我很确定问题是由于imageToMove的内存释放造成的。

iOS：dragGesture不移动元素

1 个答案: