animateWithDuration:animations:completion: in Swift

问题

In objective-C my animation bit would look something like this:

[UIView animateWithDuration:0.5 animations:^{
            [[[_storedCells lastObject] topLayerView] setFrame:CGRectMake(0, 0, swipeableCell.bounds.size.width, swipeableCell.bounds.size.height)];
        } completion:^(BOOL finished) {
            [_storedCells removeLastObject];
 }];

If I translate that into Swift it should look something like this:

 UIView.animateWithDuration(0.5, animations: {
                    self.storedCells[1].topLayerView.frame = CGRectMake(0, 0, cell.bounds.size.width, cell.bounds.size.height)
                }, completion: { (finished: Bool) in
                    //self.storedCells.removeAtIndex(1)
            })

It complains on the commented-out line. The error I receive is: Could not find an overload for 'animateWithDuration' that accepts the supplied arguments

I know the completion closure takes a boolean value and returns a void, but I should be able to write something that is not bool related there anyway....right?

Any help is appreciated.

Edit: Here is how I declare the array I'm using in the function:

var storedCells = SwipeableCell[]()

An array that takes SwipeableCell objects.

回答1:

This is a good one, tricky!

The issue is in your completion block...

A. I would begin by rewriting it like this: (not the final answer, but on our way there!)

{ _ in self.storedCells.removeAtIndex(1) }

(the _ in place of the "finished" Bool, to indicate to the reader that its value isn't being used in the block - you may also consider adding a capture list as necessary to prevent a strong reference cycle)

B. The closure you have written has a return type when it shouldn't! All thanks to Swift's handy feature "implicit returns from single expression closures" - you are returning the result of that expression, which is the element at the given index

(the type of the closure argument for completion should be ((Bool) -> Void))

This can be resolved as so:

{ _ in self.storedCells.removeAtIndex(1); return () }

来源：https://stackoverflow.com/questions/24296023/animatewithdurationanimationscompletion-in-swift

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closures

swift

ios8

animatewithduration