ios - IOS 5.1 拖放

Question

我是IOS的菜鸟。搜索了很多，但没有找到任何关于IOS拖放的好教程。我刚读到不直接支持。是否可以将项目从滚动视图拖动到视图并传递一些信息？想象一下 MAIL 应用程序。我想将一封电子邮件拖到右侧的大视图中，并与它一起传递一些信息。有什么书或教程可以教我如何制作吗？

TKS！

Answer 1

这只是使用手势识别器的问题（请参阅事件处理程序指南）。

实际的实现在一定程度上取决于你想怎么做。这是一个随机示例，其中我有一个拆分视图控件，我将左侧的 tableview 中的某些内容拖到右侧的视图中，整个拖放由长按触发（例如“点击并按住” ）。因此，我只是在 tableview 控制器的 viewDidLoad 中创建了一个手势识别器（在我的例子中，主视图控制器）：

UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(longPress:)];
[self.tableView addGestureRecognizer:longPress];

然后我定义了一个手势识别器处理程序来实现拖放，例如，

- (IBAction)longPress:(UIGestureRecognizer *)sender
{
    if (sender.state == UIGestureRecognizerStateBegan)
    {        
        // figure out which item in the table was selected

        NSIndexPath *indexPath = [self.tableView indexPathForRowAtPoint:[sender locationInView:self.tableView]];
        if (!indexPath)
        {
            inDrag = NO;
            return;
        }

        inDrag = YES;

        // get the text of the item to be dragged

        NSString *text = [NSString stringWithString:[[_objects objectAtIndex:indexPath.row] description]];

        // create item to be dragged, in this example, just a simple UILabel

        UIView *splitView = self.splitViewController.view;
        CGPoint point = [sender locationInView:splitView];
        UIFont *font = [UIFont systemFontOfSize:12];
        CGSize size = [text sizeWithFont:font];
        CGRect frame = CGRectMake(point.x - (size.width / 2.0), point.y - (size.height / 2.0), size.width, size.height);
        draggedView = [[UILabel alloc] initWithFrame:frame];
        [draggedView setFont:font];
        [draggedView setText:text];
        [draggedView setBackgroundColor:[UIColor clearColor]];

        // now add the item to the view

        [splitView addSubview:draggedView];
    }
    else if (sender.state == UIGestureRecognizerStateChanged && inDrag) 
    {
        // we dragged it, so let's update the coordinates of the dragged view

        UIView *splitView = self.splitViewController.view;
        CGPoint point = [sender locationInView:splitView];
        draggedView.center = point;
    }
    else if (sender.state == UIGestureRecognizerStateEnded && inDrag)
    {
        // we dropped, so remove it from the view

        [draggedView removeFromSuperview];

        // and let's figure out where we dropped it

        UIView *detailView = self.detailViewController.view;
        CGPoint point = [sender locationInView:detailView];

        UIAlertView *alert;
        if (CGRectContainsPoint(detailView.bounds, point))
            alert = [[UIAlertView alloc] initWithTitle:@"dropped in details view" message:nil delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil];
        else
            alert = [[UIAlertView alloc] initWithTitle:@"dropped outside details view" message:nil delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil];
        [alert show];
    }
}

显然，如果您从滚动视图中拖动子视图，您将使用以下内容替换indexPathForRowAtPoint逻辑：

    UIView *objectToDrag = nil;
    CGPoint point = [sender locationInView:myView];
    for (UIView *control in myView.subviews)
        if (CGRectContainsPoint(control.frame, point))
            objectToDrag = control;

    if (!objectToDrag)
    {
        inDrag = NO;
        return;
    }

这将帮助您确定要拖动的内容，但是从那里开始，逻辑非常相似（除了在我的示例中拖动 UILabel 之外，您将拖动 objectToDrag）。