从视图模型访问并打开 DisplayActionSheet

我的内容页面中有一个工具栏，其中有一个名为“添加”的项目，单击“添加”后我想打开DisplayActionSheet

我创造了ContentPage Toolbar in xaml并附上ICommand到视图模型中。现在DisplayActionSheet只能在视图中访问，因此我不确定如何访问它并从视图模型渲染它。

xaml 文件

<ContentPage.ToolbarItems>
    <ToolbarItem Name="" Icon="ic_add.png"    Order="Primary" Priority="0" Command="{Binding OnAddContactCommand}"/>
    <ToolbarItem Name="" Icon="ic_search.png" Order="Primary" Priority="1" Command="{Binding OnContactSearchCommand}" />
</ContentPage.ToolbarItems>

查看型号

public ICommand OnContactSearchCommand => new Command(OnContactSearch);
public ICommand OnAddContactCommand => new Command(OnAddContactSearch);

events

private async void OnAddContactSearch()
{   
   //var action = await DisplayActionSheet(AppResources.select_contact_source, AppResources.cancel, null, AppResources.manual, AppResources.phonebook);
}

private void OnContactSearch()
{
   Debug.WriteLine("OnContactSearch");
}

就像@Alessandro 说的Application.Current.MainPage也适用于操作表和警报。为了从视图模型中隐藏视图特定的内容，我创建了一个IMessageBoxService它被注入到需要它的视图模型承包商中。请注意，我正在使用Autofac IoC 容器 http://autofac.readthedocs.io/en/latest/index.html。对于 Xamarin 的 DependencyService，您已更改构造函数并在代码中查找服务。

IMessageBoxService.cs

public interface IMessageBoxService
{
    void ShowAlert(string title, string message, Action onClosed = null);
    // ...
    Task<string> ShowActionSheet(string title, string cancel, string destruction, string[] buttons = null);
}

MessageBoxService.cs

public class MessageBoxService : IMessageBoxService
{
    private static Page CurrentMainPage { get { return Application.Current.MainPage; } }

    public async void ShowAlert(string title, string message, Action onClosed = null)
    {
        await CurrentMainPage.DisplayAlert(title, message, TextResources.ButtonOK);
        onClosed?.Invoke();
    }

    public async Task<string> ShowActionSheet(string title, string cancel, string destruction = null, string[] buttons = null)
    {
        var displayButtons = buttons ?? new string[] { };
        var action = await CurrentMainPage.DisplayActionSheet(title, cancel, destruction, displayButtons);
        return action;
    }
}

应用程序安装程序.cs

    protected void RegisterDependencies(ContainerBuilder cb)
    {
        // ...
        cb.RegisterType<MessageBoxService>().As<IMessageBoxService>().SingleInstance();
    }

Usage

public class EditProductViewModel : AddProductViewModel
{
    private IMessageBoxService _messageBoxService;

    public ICommand DeleteCommand { get; set; }

    public EditProductViewModel(IPageNavigator navigator, IMessenger messenger,
        IMessageBoxService messageBoxService, TagDataStore tagDataStore) : base(navigator, messenger, tagDataStore)
    {
        _messageBoxService = messageBoxService;
        DeleteCommand = new Command(DeleteItem);
    }

...

    private async void DeleteItem()
    {
        var action = await _messageBoxService.ShowActionSheet(TextResources.MenuTitleDeleteProduct,
            TextResources.ButtonCancel, TextResources.ButtonDelete);
        if (action == TextResources.ButtonDelete)
        { } // delete

如果您正在执行视图模型优先导航（s.Xamarin https://developer.xamarin.com/guides/xamarin-forms/enterprise-application-patterns/navigation/#passing_parameters_during_navigation or 乔纳森·耶茨的博客 https://xamarinforms.wordpress.com/2014/11/21/creating-a-xamarin-forms-app-part-6-view-model-first-navigation/）您可以选择将此部分作为导航器服务的一部分。这是一个品味问题