c# - Xamarin 表单将单击的项目作为命令参数传递给命令

Question

我刚开始使用 Xamarin 表单，现在我有一个在自定义模板中显示的项目列表。

我想要的行为是事件在页面上下文中触发(使用 Corcav.Behaviors )，但我想将单击的项目传递给命令。我似乎无法让最后一部分工作。通过以下实现，事件正确触发，但传递的参数是 MyEventsListModel，但我想要被单击的项目。

请注意，我最好在 xaml/viewmodel 中而不是在代码隐藏中找到解决方案。两个事件都在 Event 上触发的替代解决方案也很好。

Xaml:

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:behaviors="clr-namespace:Corcav.Behaviors;assembly=Corcav.Behaviors"
             x:Class="TheEventsApp.Mobile.MyEventsList"
             Title="My Events"
             x:Name="MainPage">
    <ListView ItemsSource="{Binding Events}">
        <behaviors:Interaction.Behaviors>
            <behaviors:BehaviorCollection>
                <behaviors:EventToCommand EventName="ItemTapped" Command="{Binding NavigateToEventDetails}" CommandParameter="{Binding .}" />
            </behaviors:BehaviorCollection>
        </behaviors:Interaction.Behaviors>
        <ListView.ItemTemplate>
            <DataTemplate>
                <ViewCell>
                    <StackLayout Orientation="Vertical">
                        <Label Text="{Binding Name}" />
                    </StackLayout>
                </ViewCell>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
</ContentPage>

View 模型:

 [ImplementPropertyChanged]
 public class MyEventsListModel : FreshBasePageModel
 { 
    private readonly EventsDatastore eventsStore;

    public MyEventsListModel(EventsDatastore eventsStore)
    {
        this.eventsStore = eventsStore;
    }

    protected async override void ViewIsAppearing(object sender, EventArgs e)
    {
        this.Events = await eventsStore.GetMyEventsAsync();
    }

    public ObservableCollection<Event> Events { get; set; } = new ObservableCollection<Event>();

    public Command NavigateToEventDetails
    {
        get
        {
            return new Command(async (clickedEvent) =>
            {
                await CoreMethods.PushPageModel<EventDetailsPageModel>(clickedEvent);
            });
        }
    }
}

Answer 1

解决方案相当简单。在深入研究了 Corcav 的源代码之后，很容易弄明白。 EventToCommand.cs中的以下代码

private void OnFired(EventArgs e)
{
    object param = this.PassEventArgument ? e : this.CommandParameter;

    if (!string.IsNullOrEmpty(this.CommandName))
    {
        if (this.Command == null) this.CreateRelativeBinding();
    }

    if (this.Command == null) throw new InvalidOperationException("No command available, Is Command properly set up?");

    if (e == null && this.CommandParameter == null) throw new InvalidOperationException("You need a CommandParameter");

    if (this.Command != null && this.Command.CanExecute(param))
    {
        this.Command.Execute(param);
    }
}

处理它。只需将“PassEventArgument”设置为 true 即可解决我的问题。

<behaviors:EventToCommand EventName="ItemTapped" Command="{Binding NavigateToEventDetails}" PassEventArgument="True" />