Question

我将Prism与项目源一起使用，在每个选项卡式页面中都有一个Listview，对于该列表视图，我无法利用“ ItemTapped”事件作为命令事件来进行操作当点击列表视图项目时，该行为无法在ViewModel中触发命令，但是当我点击列表视图项目时，在调试模式下没有触发，请帮助我理解为什么会发生这种情况，并且是否可以使用命令来替代方法。另外，当我检查时，事件在PrismTabbedPage1.xaml.cs中触发，但在PrismTabbedPage1ViewModel.cs中未触发

原始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 },
            };
        }
    }
}

Country.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

我对Prism不熟悉，但是由于您的EventToCommand在ListView内，因此默认绑定是listview传递的数据，而不是ViewModel。

您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，您在列表视图中的绑定应该有效地重定向到视图模型中的命令。

我希望这会有所帮助。

使用Prism Xamarin表单创建动态TabbedPage

1 个答案: