问题
I have a 2 components, dependent pickerView. I have a preview UIImageView that changes each time the user uses the pickerView (and triggers the didSelectRow:inComponent:). This works just as I expected.
However, I want the pickerView to trigger didSelectRow: when the app launches, so that there is a Preview the moment the user sees the UIImageView. In viewDidLoad, when I try this:
[self pickerView:picker didSelectRow:row inComponent:component]; // row and component have 0 values.
next thing that happens - the pickerView shows up blank! Remove this line, and it works perfectly again. I tried this as well:
[picker selectRow: row inComponent:component animated:NO];
thinking that it will trigger didSelectRow: however it doesn't trigger it and my UIImageView remain blank.
Any advice on how to call the didSelectRow: method without the users help?
Update: by the way, the picker is inside another UIView (not the main one). In case it matters.
回答1:
didSelectRow:... will only be called if a row has been selected by user interaction. If you select a row programmatically with selectRow:... then you have to add you own logic to update other components like the image view.
The principle is valid for many other delegate functions, such as e.g. tableView:didSelectRowAtIndexPath:.
回答2:
Based on your comments, this what you are looking for then. Does UIPickerView's selectRow:inComponent:animated: call pickerView:didSelectRow:inComponent:?
You have to manually call the didSelectRow method.
来源：https://stackoverflow.com/questions/13075474/how-to-call-pickerview-didselectrow-incomponent-without-user-interaction