如何在ListView中隐藏禁用的MenuItem？技术解决方案求助

我明白你现在的困扰——ListView的ContextActions里的MenuItem确实没有自带的IsVisible属性，只能靠IsEnabled控制禁用状态，但你想要完全隐藏它对吧？下面给你几个可行的解决方案，都是经过实践验证的：

方案1：自定义带IsVisible属性的MenuItem #

这是最直接的方法，我们扩展原生MenuItem，给它加上IsVisible属性，通过属性变化事件来动态添加/移除ContextActions里的项：

首先创建自定义MenuItem类：

public class VisibleMenuItem : MenuItem
{
    public static readonly BindableProperty IsVisibleProperty =
        BindableProperty.Create(nameof(IsVisible), typeof(bool), typeof(VisibleMenuItem), true, propertyChanged: OnIsVisibleChanged);

    public bool IsVisible
    {
        get => (bool)GetValue(IsVisibleProperty);
        set => SetValue(IsVisibleProperty, value);
    }

    private static void OnIsVisibleChanged(BindableObject bindable, object oldValue, object newValue)
    {
        var menuItem = (VisibleMenuItem)bindable;
        var viewCell = menuItem.Parent as ViewCell;
        
        if (viewCell == null) return;

        if ((bool)newValue)
        {
            if (!viewCell.ContextActions.Contains(menuItem))
                viewCell.ContextActions.Add(menuItem);
        }
        else
        {
            viewCell.ContextActions.Remove(menuItem);
        }
    }
}

然后需要一个反转布尔值的转换器，因为你的IsCommandDissabled是“禁用时为true”，我们需要把它转成“隐藏时为false”：

public class InverseBooleanConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return !(bool)value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return !(bool)value;
    }
}

在XAML资源里声明转换器：

<ContentPage.Resources>
    <local:InverseBooleanConverter x:Key="InverseBooleanConverter"/>
</ContentPage.Resources>

最后替换原来的MenuItem为自定义控件：

<BaseControls:MenuItemsDisablingViewCell.ContextActions>
    <MenuItem IsDestructive="True" Command="{Binding EntViewModel.DeleteCom}" Text="Delete"/>
    <local:VisibleMenuItem 
        Command="{Binding DissableAndHidenCommand}" 
        Text="Command which is Dissabled and hiden" 
        IsVisible="{Binding IsCommandDissabled, Converter={StaticResource InverseBooleanConverter}}"/>
</BaseControls:MenuItemsDisablingViewCell.ContextActions>

方案2：在ViewCell后台动态管理ContextActions #

如果你不想自定义控件，也可以在MenuItemsDisablingViewCell的代码后台监听绑定上下文变化，手动添加/移除MenuItem：

public partial class MenuItemsDisablingViewCell : ViewCell
{
    private MenuItem _hiddenMenuItem;

    public MenuItemsDisablingViewCell()
    {
        InitializeComponent();
        
        // 提前创建要隐藏的MenuItem
        _hiddenMenuItem = new MenuItem
        {
            Text = "Command which is Dissabled and hiden",
            Command = new Command(() => 
            {
                if (BindingContext is YourItemType item)
                    item.DissableAndHidenCommand?.Execute(null);
            })
        };
    }

    protected override void OnBindingContextChanged()
    {
        base.OnBindingContextChanged();
        
        if (BindingContext is YourItemType item)
        {
            // 初次加载时设置可见性
            UpdateMenuItemVisibility(item.IsCommandDissabled);
            
            // 监听IsCommandDissabled的变化
            item.PropertyChanged += Item_PropertyChanged;
        }
    }

    private void Item_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName == nameof(YourItemType.IsCommandDissabled))
        {
            var item = (YourItemType)sender;
            UpdateMenuItemVisibility(item.IsCommandDissabled);
        }
    }

    private void UpdateMenuItemVisibility(bool isDisabled)
    {
        if (isDisabled)
        {
            ContextActions.Remove(_hiddenMenuItem);
        }
        else
        {
            if (!ContextActions.Contains(_hiddenMenuItem))
                ContextActions.Add(_hiddenMenuItem);
        }
    }

    // 解绑事件防止内存泄漏
    protected override void OnDisappearing()
    {
        base.OnDisappearing();
        if (BindingContext is YourItemType item)
            item.PropertyChanged -= Item_PropertyChanged;
    }
}

注意把YourItemType替换成你绑定的Items集合里的实体类型。

方案3：用Behavior管理MenuItem可见性 #

如果想保持XAML的整洁，可以用Behavior来封装这个逻辑：

public class MenuItemVisibilityBehavior : Behavior<ViewCell>
{
    public static readonly BindableProperty IsVisibleProperty =
        BindableProperty.Create(nameof(IsVisible), typeof(bool), typeof(MenuItemVisibilityBehavior), true);

    public static readonly BindableProperty MenuItemTextProperty =
        BindableProperty.Create(nameof(MenuItemText), typeof(string), typeof(MenuItemVisibilityBehavior));

    public bool IsVisible
    {
        get => (bool)GetValue(IsVisibleProperty);
        set => SetValue(IsVisibleProperty, value);
    }

    public string MenuItemText
    {
        get => (string)GetValue(MenuItemTextProperty);
        set => SetValue(MenuItemTextProperty, value);
    }

    private MenuItem _targetMenuItem;

    protected override void OnAttachedTo(ViewCell bindable)
    {
        base.OnAttachedTo(bindable);
        _targetMenuItem = bindable.ContextActions.FirstOrDefault(mi => mi.Text == MenuItemText);
        UpdateVisibility();
        bindable.BindingContextChanged += OnBindingContextChanged;
    }

    private void OnBindingContextChanged(object sender, EventArgs e) => UpdateVisibility();

    private void UpdateVisibility()
    {
        if (_targetMenuItem == null || AssociatedObject == null) return;

        if (IsVisible)
        {
            if (!AssociatedObject.ContextActions.Contains(_targetMenuItem))
                AssociatedObject.ContextActions.Add(_targetMenuItem);
        }
        else
        {
            AssociatedObject.ContextActions.Remove(_targetMenuItem);
        }
    }

    protected override void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        base.OnPropertyChanged(propertyName);
        if (propertyName == nameof(IsVisible))
            UpdateVisibility();
    }

    protected override void OnDetachingFrom(ViewCell bindable)
    {
        base.OnDetachingFrom(bindable);
        bindable.BindingContextChanged -= OnBindingContextChanged;
        _targetMenuItem = null;
    }
}

XAML里使用Behavior：

<BaseControls:MenuItemsDisablingViewCell>
    <BaseControls:MenuItemsDisablingViewCell.ContextActions>
        <MenuItem IsDestructive="True" Command="{Binding EntViewModel.DeleteCom}" Text="Delete"/>
        <MenuItem x:Name="HiddenMenuItem" Command="{Binding DissableAndHidenCommand}" Text="Command which is Dissabled and hiden"/>
    </BaseControls:MenuItemsDisablingViewCell.ContextActions>
    <BaseControls:MenuItemsDisablingViewCell.Behaviors>
        <local:MenuItemVisibilityBehavior 
            MenuItemText="Command which is Dissabled and hiden" 
            IsVisible="{Binding IsCommandDissabled, Converter={StaticResource InverseBooleanConverter}}"/>
    </BaseControls:MenuItemsDisablingViewCell.Behaviors>
</BaseControls:MenuItemsDisablingViewCell>

小提示 #

因为你用了RecycleElement缓存策略，一定要确保属性变化时能及时更新MenuItem的状态——方案1的自定义控件已经处理了这个问题，方案2和3也通过监听PropertyChanged事件保证了缓存复用后的正确性。

内容的提问来源于stack exchange，提问作者user3132499