User2363562's questions

我在 .NET MAUI 应用程序中添加了一个“附加图像”按钮，该按钮运行良好。在旁边，我添加了一个删除按钮和一个选择器，用于描述先前选择的图像的文件名：

 <!-- Attach Image Button -->
 <Button MaximumWidthRequest="150"
         Text="Attach images"
         TextColor="{StaticResource SnowWhite}"
         BackgroundColor="{StaticResource AlpineBlue}"
         CornerRadius="25"
         Command="{Binding AttachImagesCommand}">
     <Button.ImageSource>
         <FontImageSource FontFamily="MSO"
                          Glyph="{x:Static helpers:IconFont.Attach_file_add}"
                          Size="20"
                          Color="{StaticResource NightBlue}" />
     </Button.ImageSource>
 </Button>

 <!-- Delete Attached Image Button -->
 <Button BackgroundColor="{StaticResource SnowWhite}"
         Command="{Binding RemoveImageCommand}"
         IsVisible="{Binding Images, Converter={StaticResource IsListNotNullOrEmptyConverter}}">
     <Button.ImageSource>
         <FontImageSource FontFamily="MSO"
                          Glyph="{x:Static helpers:IconFont.Delete}"
                          Size="20"
                          Color="{StaticResource NightBlue}" />
     </Button.ImageSource>
 </Button>

 <!-- Images Picker -->
 <Picker
     ItemsSource="{Binding Images}"
     ItemDisplayBinding="{Binding FileName}"
     SelectedItem="{Binding CurrentImage, Mode=TwoWay}"
     SelectedIndex="{Binding CurrentImageIndex, Mode=TwoWay}"
     IsVisible="{Binding Images, Converter={StaticResource IsListNotNullOrEmptyConverter}}"
     />

删除按钮似乎也工作正常，因为它从附加的 ObservableCollection 中删除 ViewModel 中的 FileResult：

[ObservableProperty]
private FileResult _currentImage = null;

[ObservableProperty]
private int _currentImageIndex = 0;

[ObservableProperty]
private ObservableCollection<FileResult> _images = new();

// ...

[RelayCommand]
private async Task OnAttachImagesAsync()
{
    var results = await FilePicker.PickMultipleAsync(new PickOptions
    {
        PickerTitle = "Pick Image(s) Please",
        FileTypes = FilePickerFileType.Images
    });

    if (results == null)
        return;

    Images = new ObservableCollection<FileResult>(results);
    CurrentImage = Images.First();
}

// ...

[RelayCommand]
private void OnRemoveImage()
{
    Images.RemoveAt(CurrentImageIndex);
}

但是，如果 ObservableCollection 中的所有项目都已被删除，则这两个组件仍然可见：

为什么 .NET MAUI Community Toolkit 的转换器“IsListNullOrEmptyConverter”在视图开始时工作正常，但没有相应更新？Mode=TwoWay我是否错过了XAML 或NotifyCanExecuteChangedC# 中的指令？