UISegmentedControl setSelectedSegmentIndex: without valueChanged Action

Question

I'm setting the selectedSegmentIndex of an UISegmentedControl via code.
Whenever I do this the valueChanged action gets called. This sounds logical for me, but is there a way to set the selected segment without invoking the action? It should just update the display.

I've used UISegmentedControl more than once, and until now I didn't even noticed that behavior. But this time I need to present an alert if a special segment is selected. So I can't live with the invoked action if the view appears and I want to show the previous selected value.

I could disconnect the action, change the selectedValue and reconnect the action. But maybe there is a better way.

Answer 1

Your question is a sensible one; I can only suggest that you've found a bug, since this is so unusual. Usually, changing a control in code doesn't cause any control events to be emitted. Setting a UIDatePicker's date doesn't emit a Value Changed event. Setting a UIPageControl's currentPage doesn't emit a Value Changed event. Setting a UISlider's value doesn't emit a Value Changed event. Setting a UISwitch's on doesn't emit a Value Changed event. Similarly, setting a UITextField's text doesn't emit an Editing Changed event. So, the fact that changing a UISegmentedControl's selectedSegmentIndex emits a Value Changed event feels wrong. I'm going to file a bug and I think you should too.

I don't see an obvious way to determine whether the Value Changed event was triggered by the user tapping or programmatically. You'll have to raise and lower a BOOL flag or something.

EDIT: This is fixed in iOS 5.