.NET Maui 中用于自定义控件的可绑定命令始终为 null？

问题描述

我正在尝试在基于地图的自定义控件中实现可绑定命令，以便提供单击地图控件中的图钉的操作，但 CustomMap 中的 OnSelectedPin 命令始终为 null？ 我正在使用 MVVM 和 CommunityToolkit.Mvvm。

自定义地图.cs

public partial class CustomMap : Map
{
    ...

    public static readonly BindableProperty OnSelectedPinProperty =
        BindableProperty.Create(
            nameof(OnSelectedPin),
            typeof(RelayCommand),
            typeof(CustomMap));

    public RelayCommand OnSelectedPin
    {
        get { return (RelayCommand)GetValue(OnSelectedPinProperty); }
        set { SetValue(OnSelectedPinProperty, value); }
    }

    ...

    private void Pin_Clicked(object sender, PinClickedEventArgs e)
    {
        // This method gets called when a pin in the map is clicked, 
        // but OnSelectedPin is always null

        if (OnSelectedPin?.CanExecute(null) ?? false)   //<-- HERE'S THE ISSUE
        {
            OnSelectedPin.Execute(null);
        }
    }
}

我的页面.xaml

... 

<!-- Map -->
<controls:CustomMap
    Grid.Row="1"
    IsShowingUser="True"
    MapType="{Binding MapType}"
    CenterRegion="{Binding CurrentLocation}"
    OnSelectedPin="{Binding OnSelectedPinCommand}"/>

... 

我的页面.cs

public partial class MyPage : ContentPage
{
    public MyPage(MyPageViewModel ViewModel)
    {
        BindingContext = ViewModel;
        InitializeComponent();
    }
}

MyPageViewModel.cs

using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
...

public partial class MyPageViewModel : ObservableObject
{
    ...

    [RelayCommand]
    public void OnSelectedPin()
    {
        var ii = 1;  // Just for debugging purposes
    }

}