uigesturerecognizer - The UICollectionView "swipe-away" in iOS7 app manager?

Question

On any 2014+ iPhone or iPad, double-click the home button to see the "app manager"

This is a left-right UICollectionView BUT it has a "swipe-away" gesture .. swipe up. How is it done? It's not so easy to "remove" a cell from a UICollectionView.

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Footnote for googlers .. for the general problem of "peeling off", "tearing away", one cell from a collection view, here's a full tidy explanation: https://stackoverflow.com/a/24339705/294884 Hope it helps someone.

Answer 1

It can be much simpler than the comments on your question are suggesting.

Your cell should contain a view (the thing that you're going to drag off) and you add a UIPanGestureRecognizer to that view.

In the gesture's action method, you move the view up or down, and when it gets far enough off that you want to delete it, you just animate it off. There are plenty of questions here dealing with this part.

This leaves a gap in your collection and now you need to move things around. It turns out this is quite simple:

[_collectionView performBatchUpdates:^{
   [_collectionView deleteItemsAtIndexPaths:@[indexPath]];
} completion:^(BOOL finished) {
     // you might want to remove the data from the data source here so the view doesn't come back to life when the collection view is reloaded.
}];

The stuff to the right of the removed cell slides over and we're all good.

Another problem to get over: making sure your gesture recognizer and the collection view's one play nice together. Thankfully, that's not too tricky either.

[_collectionView.panGestureRecognizer requireGestureRecognizerToFail:pgr]; //where pgr is the recognizer you made for dragging the view off

This means in order for the collection view's pan gesture to do its thing, your one has to fail. So you'll want to set yours up so that it only works when panning up and down, and let the collection view still do its thing for left to right pans. In your gesture recognizers's delegate, implement the following method which simply checks if you're moving more on the x-axis or y-axis.

-(BOOL)gestureRecognizerShouldBegin:(UIPanGestureRecognizer *)gestureRecognizer
{
    CGPoint translation =[gestureRecognizer translationInView:self.view];

    return(translation.x * translation.x > translation.y * translation.y);
}