.NET MAUI 标签绑定未在 C# 中更新 - 不是 MVVM

Question

由于与 Shell 一起使用时最新的 CommunityToolkit.Maui.Mvvm 软件包存在错误，我没有使用它。所以我正在推进只是用代码编写所有内容（没有 Xaml）。据我所知，这应该可行。我希望最后更新的标签的文本得到更新，但事实并非如此。谁能看出为什么不呢？

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();
    }
}

Answer 1

您的代码有两处错误。首先，您没有设置任何控件的 BindingContext，因此即使设置正确，绑定也不会起作用。您的 Label 的定义应如下所示：

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

其次，setter对于LastUpdated属性是错误的。首先，设置支持字段值，然后调用OnPropertyChanged，这样代码就知道发生了变化并且可以传播更新后的值：

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

.NET MAUI 标签绑定未在 C# 中更新 - 不是 MVVM

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

c#

maui

.net-6.0

.net-maui