Triggering code when UIPickerView selectRow:inComponent:animated:YES is completed? - iphone

Question

My action method:
- (IBAction)buttonPressed {
// animate picker to random row (picker is a UIPickerView)
int row = random() % [self.column1 count];
[picker selectRow:row inComponent:0 animated:YES];
[picker reloadComponent:0];
// display new selected row content
int selectedRow = [picker selectedRowInComponent:0];
NSString *selectedItem = [self.column1 objectAtIndex:selectedRow];
myLabel.text = selectedItem; // UILabel under the picker
}
However
myLabel.text = selectedItem;
gets called before the animation has completed and so it doesn't display the new value.
I found the thread How to get callback from UIPickerView when the selectRow animation is done?, but the answer uses a beginAnimations/commitAnimation block - about which apple says: "Use of this method is discouraged in iOS 4.0 and later. You should use the block-based animation methods to specify your animations instead."
How would I use block-based animation to accomplish this?

Answer 1

It looks like Apple needs to update their UIPickerView API to support a block based completion handler. Until then, just wait the estimated time of the animation.
[picker selectRow:0 inComponent:0 animated:YES];
[self performSelector:#selector(setMyLabel) // setMyLabel - my function
withObject:nil
afterDelay:0.4];

Answer 2

Have you tried something like this:
[UIView animateWithDuration:2.0
delay:0.0
options:UIViewAnimationOptionCurveEaseInOut
animations:^{
// the animation code
[myPickerView selectRow:0 inComponent:0 animated:YES];
}
completion:^(BOOL finished) {
[self performSelector:#selector(setMyLabel)];
}
];
Or you could just set the label directly in the completion block, if that's the only thing you want to do after the animation completes.
EDIT:
The code above is the same as the code in the other thread you've mentioned, but using animation blocks instead. I actually didn't know if the method selectRow:inComponent:animated: will run on the same animation block thread or it will have its own thread. Since it didn't work, that means it runs on its own thread so the code I wrote won't work.
There is one way around to solve this, which is by blocking the main thread for the time needed for the animation to complete. You can call [NSThread sleepForTimeInterval:1.0] after your call to selectRow:inComponent:animated:, and you can adjust the interval until you reach a suitable value. Note that blocking the main thread is highly discouraged by Apple. Personally I would block it only if I couldn't think of another way to achieve what I'm trying to do and if the blocking time is smaller than 1.