A segmented control is not a good choice when you really want the behavior of a UIButton
for your prev/next controls.
What I think is happening is that you are initializing the toolbar with the segmented control and no segment selected. So when you tap prev/next the first time, the value changes and that segment is selected for that specific segmented control. As you continue to tap prev/next, eventually you get to a segmented control that already has a segment selected and that segment will not fire a value changed event when tapped because it is already the selected segment.
You can explicitly deselect the selected segment in your switchTextField:
method (make sure you don't trigger switchTextField:
recursively) or you can change your implementation to use UIButton
objects for prev/next instead of the segmented control.
I recommend going with UIButton
.