Xamarin forms: Getting NotImplementedException

Question

I have a switch in my listview. In xaml, a converter added for the IsToggled property:

<Switch
          IsToggled="{Binding userProfileTO.userId, Converter={StaticResource isToggledConverter}}"
          HorizontalOptions="EndAndExpand"
          VerticalOptions="CenterAndExpand"/>

Converter code:

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
    bool toggle = false;
    // My Codes
    return toggle;
}

public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
    throw new NotImplementedException();
}

Getting an NotImplementedException on ConvertBack when running this code.

Exception thrown: 'System.NotImplementedException' in Myprojectname.dll
An exception of type 'System.NotImplementedException' occurred in Myprojectname.dll but was not handled in user code
The method or operation is not implemented.

You don't have the convertback method implemented, so it's normal you will get a NotImplementedException. — Bruno Caceiro, Oct 01 '18 at 12:30
You are explicitly throwing a NotImplementedException, so of course you are getting a NotImplementedException. It's doing EXACTLY what you are telling it to do. — Jason, Oct 01 '18 at 13:01

score 3 · Accepted Answer · answered Oct 01 '18 at 13:35

3

The default binding type of IsToggled property is "Two-way". That's why your ConvertBack function is getting called. You can simply remove the

throw new NotImplementedException();

in your ConvertBack method and everything will work fine.

Or if you don't wanna do that you can explicitly set the binding mode to be One-way

answered Oct 01 '18 at 13:35

Aritra Das

262
3
8

If I remove that code, what can I give instead of that? ConvertBack method should return value, is return false is enough? – Sreejith Sree Oct 02 '18 at 03:30
https://stackoverflow.com/questions/52604115/xamarin-forms-current-listview-switch-state-changing-when-the-listview-gets-ref#52605968 – Sreejith Sree Oct 02 '18 at 11:12
That will make your code error-prone, better to switch to One-way binding mode. – Aritra Das Oct 03 '18 at 06:25

Xamarin forms: Getting NotImplementedException

1 Answers1