Out of Bounds Error when Deselecting Segment - ios

Question

I am attempting to programmatically deselect a UISegmentedControl from within Xamarin whenever the user re-taps the selected segment. I have created an inherited class that will determine if this is required, but whenever I try to set SelectedSegment to -1, the application bombs out, throwing an out of bounds exception.
public class UIDeselectableSegmentedControl : UISegmentedControl
{
private int previouslySelectedIndex = -1;
private bool isIOS7
{
get
{
return UIDevice.CurrentDevice.CheckSystemVersion(7, 0);
}
}
public UIDeselectableSegmentedControl()
{
this.ValueChanged += UIDeselectableSegmentedControl_ValueChanged;
}
void UIDeselectableSegmentedControl_ValueChanged(object sender, EventArgs e)
{
if (previouslySelectedIndex == this.SelectedSegment)
{
this.SelectedSegment = -1;
}
previouslySelectedIndex = this.SelectedSegment;
}
public override void TouchesBegan(NSSet touches, UIEvent evt)
{
int initialIndex = this.SelectedSegment;
base.TouchesBegan(touches, evt);
//Pre-iOS7 Segment Changes are present in Touches Began
if (!isIOS7) CheckSelectedSegment(initialIndex, this.SelectedSegment);
}
public override void TouchesEnded(NSSet touches, UIEvent evt)
{
int initialIndex = this.SelectedSegment;
base.TouchesEnded(touches, evt);
//Post-iOS7 Segment Changes are present in Touches Ended
if (isIOS7) CheckSelectedSegment(initialIndex, this.SelectedSegment);
}
/// <summary>
/// Compare the SelectedSegment with the Current Index value. If it is the same, raise the Value Changed event.
/// </summary>
/// <param name="index">Currently Selected Segment</param>
private void CheckSelectedSegment(int oldIndex, int newIndex)
{
if (oldIndex == newIndex)
{
this.SendActionForControlEvents(UIControlEvent.ValueChanged);
}
}
}
If I change it to this.SelectedSegment = 0 then the control will successfully force the SegementedControl to the first item whenever you re-tap another selected item, but if I have it to set it to -1, then it throws the following exception:
* Terminating app due to uncaught exception 'NSRangeException', reason: '* -[__NSArrayM objectAtIndex:]: index 4294967295 beyond bounds [0 .. 1]'
Is there a different way I should be deselecting the segment? According to this answer this is the correct way in Objective-C, and the Metadata comment on SelectedSegment indicates this is it correct:
//
// Summary:
// The index of the selected segment.
//
// Remarks:
// Set to -1 to turn off the currently selected segment. If MonoTouch.UIKit.UISegmentedControl.Momentary
// == true the SelectedSegment property is ignored.

Answer 1

In typical form, I think I've solved my own issue. I'm not sure why (perhaps someone can clarify this), but it seems to be something to do with trying to change the SelectedSegment within the ValueChanged event. Possibly some sort of mutation exception essentially.
I've reworked my code, so that the method called within TouchesEnded/Began just makes the change itself directly, rather than forcing ValueChanged to be called and changing it itself. In a way, that makes more sense, since ValueChanged is reacting to a change - it probably shouldn't be responsible for making the change:
public class UIDeselectableSegmentedControl : UISegmentedControl
{
private bool isIOS7
{
get
{
return UIDevice.CurrentDevice.CheckSystemVersion(7, 0);
}
}
public override void TouchesBegan(NSSet touches, UIEvent evt)
{
int initialIndex = this.SelectedSegment;
base.TouchesBegan(touches, evt);
//Pre-iOS7 Segment Changes are present in Touches Began
if (!isIOS7) DeselectSegmentIfApplicable(initialIndex, this.SelectedSegment);
}
public override void TouchesEnded(NSSet touches, UIEvent evt)
{
int initialIndex = this.SelectedSegment;
base.TouchesEnded(touches, evt);
//Post-iOS7 Segment Changes are present in Touches Ended
if (isIOS7) DeselectSegmentIfApplicable(initialIndex, this.SelectedSegment);
}
/// <summary>
/// Compare the SelectedSegment with the Current Index value. If it is the same, raise the Deselect the Segment.
/// </summary>
/// <param name="oldIndex">the previously selected segment</param>
/// <param name="newIndex">The newly selected segment</param>
private void DeselectSegmentIfApplicable(int oldIndex, int newIndex)
{
if (oldIndex == newIndex)
{
this.SelectedSegment = -1;
}
}
}