mvvm - 使用 Prism Xamarin 表单创建动态 TabbedPage

Question

我正在将 Prism 与项目源一起使用，在每个选项卡式页面内都有一个 Listview，我无法将“ItemTapped”事件用作命令行为的事件，以在点击 listview 项目时触发 viewmodel 中的命令，但没有触发器在 Debug模式下，当我点击 ListView 项时，请帮助我理解为什么会发生这种情况，是否有任何替代方式可以让我使用命令。此外，当我检查事件在 PrismTabbedPage1.xaml.cs 中被触发但在 PrismTabbedPage1ViewModel.cs 中没有被触发

Prism Xamarin 形式

PrismTabbedPage1.Xaml

<?xml version="1.0" encoding="utf-8" ?>
 <TabbedPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms" xmlns:behaviors="clr-namespace:Prism.Behaviors;assembly=Prism.Forms" prism:ViewModelLocator.AutowireViewModel="True" x:Class="testapp.Views.PrismTabbedPage1" ItemsSource="{Binding countries}"> <TabbedPage.ItemTemplate> 
<DataTemplate> 
<ContentPage Title="{Binding CountryName}">
 <ListView ItemsSource="{Binding Cities}"> 
<ListView.ItemTemplate>
 <DataTemplate>
 <ViewCell> 
<Label Text="{Binding CityName}" TextColor="Black"/> 
</ViewCell>
 </DataTemplate>
 </ListView.ItemTemplate> 
<ListView.Behaviors> 
<behaviors:EventToCommandBehavior EventName="ItemTapped" Command="{Binding ListItemTapped}" EventArgsParameterPath="Item"/> 
</ListView.Behaviors> </ListView>
 </ContentPage>
 </DataTemplate>
 </TabbedPage.ItemTemplate>
 </TabbedPage>`

PrismTabbedPage1ViewModel.cs

using Prism.Mvvm;
using Prism.Navigation;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using testapp.Models;


namespace testapp.ViewModels
{
    public class PrismTabbedPage1ViewModel : BindableBase
    {
        public ObservableCollection<Country> countries { get; set; }
        public DelegateCommand<Country> ListItemTapped => new DelegateCommand<Country>(OnTapped);

        private void OnTapped(Country obj)
        {

            //NavigationService.NavigateAsync("MainPage");
        }

        public PrismTabbedPage1ViewModel()
        {
            ObservableCollection<City> Cities1 = new ObservableCollection<City>()
            {
                new City(){ CityName = "City1" },new City(){ CityName = "City2" },new City(){ CityName = "City3" },
                new City(){ CityName = "City4" },new City(){ CityName = "City5" },new City(){ CityName = "City6" },
                new City(){ CityName = "City7" },new City(){ CityName = "City8" },new City(){ CityName = "City9" },
            };


            countries = new ObservableCollection<Country>()
            {
                new Country(){ CountryName = "Country 1", Cities = Cities1 },
                new Country(){ CountryName = "Country 2", Cities = Cities1 },
                new Country(){ CountryName = "Country 3",  Cities = Cities1 },
            };
        }
    }
}

国家.cs

using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Text;

namespace testapp.Models
{
public class Country
{
public string CountryName { get; set; }
public ObservableCollection Cities { get; set; }
}
public class City
{
public string CityName { get; set; }


}

}

在此代码中，不会触发 listview 命令行为。

Answer 1

我不熟悉 Prism，但由于您的 EventToCommand 在 ListView 内，因此您的默认绑定(bind)是 ListView 传递的数据，而不是您的 ViewModel。

你可以尝试这样的事情:

<behaviors:EventToCommandBehavior EventName="ItemTapped"
                         Command="{Binding Source={x:Reference this},Path=BindingContext.ListItemTapped}"
                         EventArgsParameterPath="{Binding .}"/>

并为您的页面命名:

 <TabbedPage .... x:Name="this">

因此，您在 ListView 中的绑定(bind)应该有效地重定向到 View 模型中的命令。

我希望这有帮助。