C# CommunityToolkit.Mvvm ObservableProperty on a list

Question

I want to try the Community Toolkit 8.0 the MVVM part.

I have a very simple application:

.... 
       d:DataContext="{d:DesignInstance Type=local:MainWindowViewModel}"
.... 
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="12*" />
        </Grid.RowDefinitions>
        <Button x:Name="ButtonDirectory" Grid.Row="0" Grid.Column="0" Margin="50 2 0 2" Width="200" Content="List Directory" Command="{Binding ClickButtonListDirectoryCommand, Mode=OneWay}" />
        <ListView x:Name="ListViewDirectories" Grid.Row="1" Grid.Column="0" ItemsSource="{Binding DirectoriesNames}"  />
    </Grid>

and this is my viewmodel:

public partial class MainWindowViewModel : ObservableObject
{
    [ObservableProperty]
    List<string> _directoriesNames = new();

    [RelayCommand]
    private void ClickButtonListDirectory()
    {
        this.DirectoriesNames.Add("Hello");
    }
}

This construct works, when I use string instead of a list - but obviously I want to use something like a list when my view component is a ListView.

The directoriesNames itself gets updated (saw that in the debugger) but it's not displayed in the view (ListView).

Can someone help me out with that?

Thanks.

Andrew KeepCoding · Accepted Answer · 2025-03-07 21:55:49Z

11

Change your List to ObservableCollection.

This code will notify the UI when the DirectoriesNames itself is changed but the only change you are making to DirectoriesNames is instantiating it.

[ObservableProperty]
List<string> _directoriesNames = new();

The ObservableCollection notifies the UI when you add or remove items.

[ObservableProperty]
ObservableCollection<string> _directoriesNames = new();

edited Mar 7 at 21:55

answered Aug 21, 2022 at 12:28

Andrew KeepCoding

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1 Comment

Enki Over a year ago

Yeps, that's it. Thank you very much for the additional explanation why List will not work :-)

HarshBangera · Accepted Answer · 2022-08-21 12:29:50Z

6

You need to use ObservableCollection :-

ObservableCollection<string> DirectoriesNames = new();

edited Aug 21, 2022 at 12:29

answered Aug 21, 2022 at 12:26

HarshBangera

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1 Comment

Neeraj Over a year ago

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

Chris Berlin · Accepted Answer · 2024-11-30 11:36:02Z

0

Getting answers together: use [ObservableProperty] ObservableCollection

Full sample:

public partial class MainWindowViewModel : ObservableObject
{
    [ObservableProperty]
    ObservableCollection<string> _directoriesNames = new();

    [RelayCommand]
    private void ClickButtonListDirectory()
    {
        this.DirectoriesNames.Add("Hello");
    }
}

answered Nov 30, 2024 at 11:36

Chris Berlin

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