本次的 cookbook-style 教程中介绍如何通过长按手势来移动 table view中的cell,这种操作方式就像苹果自家的天气 App 一样。
你可以直接把本文中的到吗添加到你的工程中,或者将其添加到我为你创建好的 starter project 中,也可以下载本文的完整示例工程。
你需要什么?
- UILongGestureRecognizer
- UITableView (可以用 UICollectionView 替代之)
- UITableViewController (可以用 UIViewController 或 UICollectionViewController 替代之)
- 5 分钟。
如何做?
首先给 table view 添加一个 UILongGestureRecognizer
。可以在 table view controller 的 viewDidLoad
方法中添加。
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UILongPressGestureRecognizer
*longPress = [[UILongPressGestureRecognizer alloc] initWithTarget:self
action:@selector(longPressGestureRecognized:)]; [self.tableView
addGestureRecognizer:longPress]; |
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-
(IBAction)longPressGestureRecognized:(id)sender { UILongPressGestureRecognizer
*longPress = (UILongPressGestureRecognizer *)sender; UIGestureRecognizerState
state = longPress.state; CGPoint
location = [longPress locationInView:self.tableView]; NSIndexPath
*indexPath = [self.tableView indexPathForRowAtPoint:location]; //
More coming soon... } |
接着你需要处理UIGestureRecognizerStateBegan
分支。如果获取到一个有效的 index path(non-nil),就去获取对应的 UITableViewCell
,并利用一个 helper 方法获取这个 table view cell
的 snapshot view。然后将这个 snapshot view 添加到 table view 中,并将其 center 到对应的 cell上。
为了更好的用户体验,以及更自然的效果,在这里我把原始 cell 的背景设置为黑色,并给 snapshot view 增加淡入效果,让 snapshot view 比 原始 cell 稍微大一点,将它的Y座标偏移量与手势的位置的Y轴对齐。这样处理之后,cell 就像从 table view 中跳出,然后浮在上面,并捕捉到用户的手指。
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static
UIView *snapshot = nil; ///<
A snapshot of the row user is moving. static
NSIndexPath *sourceIndexPath = nil; ///<
Initial index path, where gesture begins. switch
(state) { case
UIGestureRecognizerStateBegan: { if
(indexPath) { sourceIndexPath
= indexPath; UITableViewCell
*cell = [self.tableView cellForRowAtIndexPath:indexPath]; //
Take a snapshot of the selected row using helper method. snapshot
= [self customSnapshotFromView:cell]; //
Add the snapshot as subview, centered at cell's center... __block
CGPoint center = cell.center; snapshot.center
= center; snapshot.alpha
= 0.0; [self.tableView
addSubview:snapshot]; [UIView
animateWithDuration:0.25 animations:^{ //
Offset for gesture location. center.y
= location.y; snapshot.center
= center; snapshot.transform
= CGAffineTransformMakeScale(1.05, 1.05); snapshot.alpha
= 0.98; //
Black out. cell.backgroundColor
= [UIColor blackColor]; }
completion:nil]; } break ; } //
More coming soon... } |
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-
(UIView *)customSnapshotFromView:(UIView *)inputView { UIView
*snapshot = [inputView snapshotViewAfterScreenUpdates:YES]; snapshot.layer.masksToBounds
= NO; snapshot.layer.cornerRadius
= 0.0; snapshot.layer.shadowOffset
= CGSizeMake(-5.0, 0.0); snapshot.layer.shadowRadius
= 5.0; snapshot.layer.shadowOpacity
= 0.4; return
snapshot; } |
UIGestureRecognizerStateChanged
分支,此时需要移动
snapshot view(只需要设置它的 Y 轴偏移量即可)。如果手势移动的距离对应到另外一个 index path,就需要告诉 table view,让其移动 rows。同时,你需要对 data source 进行更新:
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case
UIGestureRecognizerStateChanged: { CGPoint
center = snapshot.center; center.y
= location.y; snapshot.center
= center; //
Is destination valid and is it different from source? if
(indexPath && ![indexPath isEqual:sourceIndexPath]) { //
... update data source. [self.objects
exchangeObjectAtIndex:indexPath.row withObjectAtIndex:sourceIndexPath.row]; //
... move the rows. [self.tableView
moveRowAtIndexPath:sourceIndexPath toIndexPath:indexPath]; //
... and update source so it is in sync with UI changes. sourceIndexPath
= indexPath; } break ; } //
More coming soon... |
最后,当手势结束或者取消时,table view 和 data source 都是最新的。你所需要做的事情就是将 snapshot view 从 table view 中移除,并把 cell 的背景色还原为白色。
为了提升用户体验,我们将 snapshot view 淡出,并让其尺寸变小至与 cell 一样。这样看起来就像把 cell 放回原处一样。
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default :
{ //
Clean up. UITableViewCell
*cell = [self.tableView cellForRowAtIndexPath:sourceIndexPath]; [UIView
animateWithDuration:0.25 animations:^{ snapshot.center
= cell.center; snapshot.transform
= CGAffineTransformIdentity; snapshot.alpha
= 0.0; //
Undo the black-out effect we did. cell.backgroundColor
= [UIColor whiteColor]; }
completion:^(BOOL finished) { [snapshot
removeFromSuperview]; snapshot
= nil; }]; sourceIndexPath
= nil; break ; } |
就这样,搞定了!编译并运行程序,现在可以通过长按手势对 tableview cells重新排序!