A quick question about the UISegmentedControl class on the iPhone.
Hopefully, some may have noticed how in its default state with 2 segments, the segmented control still will toggle even if the user taps on a segment that is currently selected.
I've seen UISegmentedControls in apps that negate that behaviour and don't toggle when the user presses a selected segment. Namely, Apple's iTune Store app.
Is there a simple way of preventing this behaviour that I'm overlooking, or do I need to write some logic into the valueChanged?
I've been trying to disable currently selected segments and enabling unselected ones, but this seems to change the appearance of the control when I don't want it do.
Any ideas?
Look in the UISegmentedControl.h header file (an easy way is to double click on "UISegmentedControl" in XCode with Command held down).
In there you'll see a number of items in a _segmentedControlFlags struct. If you make a category on UISegmentedControl, you can manipulate any of those elements - including dontAlwaysToggleForTwoSegments which as you might guess by the name is what you are looking for.
Since this is documented in the API header (though not in the actual documentation) it should be pretty safe to use.
This default behavior has been changed in the 3.0 API.
In 3.0, "_segmentedControlFlags" has been changed to the "momentary" property, which can still be found in the UISegmentedControl.h header file.
Accessing the _segmentedControlFlags via an Category is considered as use of a private API and thus a violation of the License Agreement by Apple, as I had to learn today. Until now, I thought, Categories are a language feature to fix someone elses horrible class design...
来源：https://stackoverflow.com/questions/633924/uisegmentedcontrol-behaviour