.NET MAUI Label Binding not updating in C# - Not MVVM

Question

Due to a bug with the latest CommunityToolkit.Maui.Mvvm package when used with Shell, I'm not using it. So I'm pushing ahead just writing everything in code (no Xaml). From what I can tell, this should work. I'm expecting the text of the last updated label to be updated, but it doesn't. Can anyone see why not?

namespace MyMauiApp;

public class DashboardPage : ContentPage
{
    private string _lastUpdated;
    private bool _loading;

    public DashboardPage()
    {
        LoadData = new AsyncCommand(SetData);

        RefreshView refreshView = new();
        refreshView.RefreshColor = ColourConstants.DesaturatedDark;
        refreshView.Bind(RefreshView.IsRefreshingProperty, nameof(_loading));
        refreshView.Bind(RefreshView.CommandProperty, nameof(LoadData));

        ScrollView scrollView = new();
        var dashgrid = new Grid
        {
            RowDefinitions =
            {
                new RowDefinition { Height = new GridLength(0, GridUnitType.Auto) },                
            },
            ColumnDefinitions =
            {
                new ColumnDefinition { Width = new GridLength(0, GridUnitType.Auto) },
                new ColumnDefinition { Width = new GridLength(0, GridUnitType.Auto) },
            },
        }.CenterVertical();

        dashgrid.Add(new Label { Text = "Last Updated:" }, 0, 0);
        Label lastUpdated = new() { HorizontalTextAlignment = TextAlignment.End };
        lastUpdated.SetBinding(Label.TextProperty, nameof(LastUpdated));
        dashgrid.Add(lastUpdated, 1, 0);

        scrollView.Content = dashgrid;
        refreshView.Content = scrollView;
        Content = refreshView;
    }

    public string LastUpdated
    {
        get => _lastUpdated;
        set
        {
            OnPropertyChanged(nameof(LastUpdated));
            _lastUpdated = value;
        }
    }

    public AsyncCommand LoadData { get; }

    private async Task SetData()
    {
        try
        {
            LastUpdated = DateTime.Now.ToString("dd/MM/yy hh:mm tt");
        }
        catch (Exception)
        {
            Debug.WriteLine("Failed to set data");
        }
        finally
        {
            _loading = false;
        }
    }

    protected override void OnAppearing()
    {
        base.OnAppearing();
        _ = SetData();
    }
}

user_575432 · Answer

There are two things wrong with your code. First, you are not setting the BindingContext of any controls, so the bindings won't work even if they are set up correctly. The definition of your Label should look like this:

Label lastUpdated = new() { HorizontalTextAlignment = TextAlignment.End };
lastUpdated.BindingContext = this;
lastUpdated.SetBinding(Label.TextProperty, nameof(LastUpdated));

Secondly, the setter for the LastUpdated property is wrong. First, you set the backing field value, then call OnPropertyChanged so the code knows that there was a change and the updated value can be propagated:

public string LastUpdated
{
    get => _lastUpdated;
    set
    {
        _lastUpdated = value;
        OnPropertyChanged(nameof(LastUpdated));
    }
}

.NET MAUI Label Binding not updating in C# - Not MVVM

1 Answers