iOS-检测UITableViewCell是否被移出可见视图? [英] iOS - Detect UITableViewCell being moved out of the visible view?
问题描述
该单元格在屏幕上不再可见时,需要通知我.
As soon as the cell is no longer visible on the screen I need to be notified.
UITableView已经有一个名为 tableView:didEndDisplayingCell:forRowAtIndexPath:
的委托方法,但是从未调用过该委托方法.是的,我确实为我的UITableView设置了委托.
UITableView already has a delegate method called tableView:didEndDisplayingCell:forRowAtIndexPath:
but this delegate method never gets called. And yes I do have the delegate for my UITableView set.
还有其他方法可以检测到被移除的细胞吗?我需要能够保存此单元格的内容(输入),然后再将其用于其他项目.
Any other ways to detect a cell being removed? I need to be able to save the content (inputs) of this cell before it's being reused by another item.
根据文档 tableView:didEndDisplayingCell:forRowAtIndexPath:
是iOS 6和更高版本的API.有没有办法在iOS 5上实现这一目标?
According to the documentation tableView:didEndDisplayingCell:forRowAtIndexPath:
is iOS 6 and higher API. Is there a way to achieve this on iOS 5?
推荐答案
在低于6.0的iOS版本上,表格视图不会发送 tableView:didEndDisplayingCell:forRowAtIndexPath:
消息.
On versions of iOS older than 6.0, the table view doesn't send the tableView:didEndDisplayingCell:forRowAtIndexPath:
message.
如果您使用的是 UITableViewCell
的子类,则可以通过覆盖 didMoveToWindow
:
If you are using a subclass of UITableViewCell
, you can get the same effect on older versions of iOS by overriding didMoveToWindow
:
- (void)didMoveToWindow {
if (self.window == nil) {
// I have been removed from the table view.
}
}
您可能需要给单元格一个(弱或unsafe_unretained)引用,以供您返回给表视图委托,以便您可以向委托发送消息.
You may need to give your cell a (weak or unsafe_unretained) reference back to your table view delegate so you can send the delegate a message.
但是,您不能仅依赖于 didMoveToWindow
的所有版本的iOS.在iOS 6之前,表视图始终在重用之前将表视图单元格作为子视图删除,因此该单元格在重用之前始终会收到 didMoveToWindow
.但是,从iOS 6开始,表格视图可以重用单元格,而无需将其删除为子视图.表格视图将仅更改单元格的框架以将其移动到新位置.这意味着从iOS 6开始,单元在重用之前不会不总是收到 didMoveToWindow
.
However, you can't rely only on didMoveToWindow
for all versions of iOS. Before iOS 6, a table view always removed a table view cell as a subview before reusing it, so the cell would always receive didMoveToWindow
before being reused. However, starting in iOS 6, a table view can reuse a cell without removing it as a subview. The table view will simply change the cell's frame to move it to its new location. This means that starting in iOS 6, a cell does not always receive didMoveToWindow
before being reused.
因此,您应该在单元格子类中实现 didMoveToWindow
,并在委托中实现 tableView:didEndDisplayingCell:forRowAtIndexPath:
,并确保如果两者都被调用,则可以实现,或者如果只叫一个.
So you should implement both didMoveToWindow
in your cell subclass, and tableView:didEndDisplayingCell:forRowAtIndexPath:
in your delegate, and make sure it works if both are called, or if just one is called.
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