NavigationView.ClearValue(NavigationView.MenuItemsProperty) 总是抛出 System.ArgumentException

Question

var temp = new NavigationView();
temp.ClearValue(NavigationView.MenuItemsProperty);

// System.ArgumentException: 'Value does not fall within the expected range.'
// Exception occurred: 'System.ArgumentException'(WinRT.Runtime.dll)
// WinRT Infomation: Argument 'source' is null.

即使 temp.ReadLocalValue(NavigationView.MenuItemsProperty) 不返回 DependencyProperty.UnsetValue，也会出现同样的结果。

如何才能达到调用SetBinding前先调用ClearValue的效果？

Answer 1

ClearValue

不适合清除

MenuItems

控件的

NavigationView

集合，因为它旨在清除依赖属性的本地值，而不是操作集合的内容。

试试这个：

var temp = new NavigationView();
temp.MenuItems.Clear();

Answer 2

首先，如果你想切换菜单项源，你需要定位

MenuItemsSourceProperty

，而不是

MenuItemsProperty

。

<Grid RowDefinitions="Auto,*">
    <StackPanel Orientation="Horizontal">
        <Button
            Click="MenuItemsAButton_Click"
            Content="MenuItemsA" />
        <Button
            Click="MenuItemsBButton_Click"
            Content="MenuItemsB" />
    </StackPanel>
    <NavigationView
        x:Name="NavigationViewControl"
        Grid.Row="1" />
</Grid>

public sealed partial class MainPage : Page
{
    public MainPage()
    {
        this.InitializeComponent();
    }

    public ObservableCollection<string> MenuItemsA { get; set; } = new()
    {
        "Menu Item 1",
        "Menu Item 2",
        "Menu Item 3",
    };

    public ObservableCollection<string> MenuItemsB { get; set; } = new()
    {
        "Menu Item 4",
        "Menu Item 5",
        "Menu Item 6",
    };

    private void BindMenuItemsTo(string menuItemsPropertyName)
    {
        if (this.NavigationViewControl.MenuItemsSource is not null)
        {
            this.NavigationViewControl.ClearValue(NavigationView.MenuItemsSourceProperty);
        }

        this.NavigationViewControl.SetBinding(
            NavigationView.MenuItemsSourceProperty,
            new Binding()
            {
                Source = this,
                Path = new PropertyPath(menuItemsPropertyName),
            });
    }

    private void MenuItemsAButton_Click(object sender, RoutedEventArgs e)
    {
        this.BindMenuItemsTo("MenuItemsA");
    }

    private void MenuItemsBButton_Click(object sender, RoutedEventArgs e)
    {
        this.BindMenuItemsTo("MenuItemsB");
    }
}