CODEWITHSUNDEEP
c#xamlmvvmxamarin.forms
redcurry
redcurry

Reputation: 2497

Why aren't the items in a Picker (Xamarin.Forms) updated after raising PropertyChanged?

I've set up a Picker so that each item is shown with a random number appended to it (via a converter). I've also added a button that raises the PropertyChanged event on the list, so that the items are shown with a new set of random numbers. However, even though the PropertyChanged event is being raised, the items don't appear to be updated.

Here's the XAML layout with the Picker and Button:

<StackLayout>
    <Picker
        ItemsSource="{Binding MyList}"
        ItemDisplayBinding="{Binding ., Converter={StaticResource MyConverter}}"
        />
    <Button
        Command="{Binding RefreshCommand}"
        Text="Refresh"
        />
</StackLayout>

Here's the view model, which contains MyList and RefreshCommand. The RefreshCommand raises the PropertyChanged event for MyList (via ViewModelBase, which is part of the MVVM Light Toolkit):

public class MainViewModel : ViewModelBase
{
    private ObservableCollection<MyEnum> _myList;
    public ObservableCollection<MyEnum> MyList
    {
        get => _myList;
        set => Set(ref _myList, value);
    }

    public ICommand RefreshCommand =>
        new RelayCommand(() => RaisePropertyChanged(nameof(MyList)));
}

public enum MyEnum
{
    One, Two, Three, Four, Five
}

Here's the converter, which appends a random number to the given value:

public class MyConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var random = new Random();
        return $"{value} {random.Next(100)}";
    }

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

Things work when the page is first displayed: each item in MyList is shown with a random number appended to it. However, when I click on the Refresh button, which raises the PropertyChanged event for MyList (I verified this), the items in the Picker are not re-evaluated. I expected new random numbers to show up but it's the same numbers as before (in other words, nothing happens).

Upvotes: 0

Views: 348

Answers (1)

Ax1le
Ax1le

Reputation: 6643

You have to reset the Picker's items source like:

RefreshCommand = new Command( async () =>
{
    ObservableCollection<MyEnum> list = MyList;
    MyList = null;
    await Task.Delay(10);
    MyList = list;
});

It will trigger the converter again to refreh the random value.

Upvotes: 1

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