xamarin.forms - 如何为具有棱镜的 Xamarin 表单中的内容视图创建单独的视图模型?
问题描述
问题陈述 我想创建一个 contentview 用户控件,它有自己的视图模型,可以在多个内容页面中使用。
下面的实现中的问题我已经扩展了我的 App.xaml.cs,如下所述。但是,一旦导航从具有 contentview 用户控件的 contentpage 工作,但如果我再次导航到该页面,导航将不起作用。只是为了添加它, view.Parent 在下面的代码中也为空。
请帮忙。
using OEP.Views;
using Prism;
using Prism.Common;
using Prism.Ioc;
using Prism.Mvvm;
using Prism.Navigation;
using Prism.Unity;
using Unity.Resolution;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
[assembly: XamlCompilation(XamlCompilationOptions.Compile)]
namespace OEP
{
public partial class App : PrismApplication
{
public App() : this(null) { }
public App(IPlatformInitializer initializer) : base(initializer) { }
protected override async void OnInitialized()
{
InitializeComponent();
//await NavigationService.NavigateAsync("NewOrderPage");
await NavigationService.NavigateAsync("LoginPage");
//await NavigationService.NavigateAsync("HomePage");
}
protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.RegisterForNavigation<LoginPage>();
containerRegistry.RegisterForNavigation<ForgotPasswordPage>();
containerRegistry.RegisterForNavigation<HomePage>();
containerRegistry.RegisterForNavigation<CustomerDetailsPage>();
containerRegistry.RegisterForNavigation<NewOrderPage>();
//Container.Resolve<HomePageCustomersUserControl>("Customers");
//containerRegistry.Register<HomePageCustomersUserControl, HomePageCustomersUserControlViewModel>();
//ViewModelLocationProvider.Register<HomePageCustomersUserControl>(() => Container.Resolve<HomePageCustomersUserControlViewModel>());
}
protected override void ConfigureViewModelLocator()
{
ViewModelLocationProvider.SetDefaultViewModelFactory((view, type) =>
{
Page page = null;
switch (view)
{
case Page page1:
page = page1;
break;
case Element customView:
page = GetPageFromElement(customView);
// Existing parameter with the Page
break;
}
var navService = CreateNavigationService(page);
ParameterOverrides overrides = new ParameterOverrides
{
{ "navigationService", navService }
};
return Container.GetContainer().Resolve(type, type.GetType().Name, overrides);
});
}
// Currently exists
protected INavigationService CreateNavigationService(Page page)
{
var navigationService = NavigationService;
((IPageAware)navigationService).Page = page;
return navigationService;
}
protected INavigationService CreateNavigationService(object view)
{
switch (view)
{
case Page page:
return CreateNavigationService(page);
case Element element:
var parentPage = GetPageFromElement(element);
if (parentPage == null)
{
return null;
}
return CreateNavigationService(parentPage);
default:
return null;
}
}
private Page GetPageFromElement(Element view)
{
switch (view.Parent)
{
case Page page:
return page;
case null:
return null;
default:
return GetPageFromElement(view.Parent);
}
}
protected override void OnStart()
{
// Handle when your app starts
}
protected override void OnSleep()
{
// Handle when your app sleeps
}
protected override void OnResume()
{
// Handle when your app resumes
}
}
}
解决方案
这在 Prism 7.1 中得到支持。以下内容直接取自 Prism 单元测试。如果您遵循命名约定,您实际上不需要注册任何内容,您只需设置 ViewModelLocator.AutowirePartialView 并引用父页面。
<ContentView
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="Prism.DI.Forms.Tests.Mocks.Views.PartialView">
<StackLayout>
<Label Text="{Binding SomeText}" />
<Button Command="{Binding NavigateCommand}"
x:Name="navigateButton" />
</StackLayout>
</ContentView>
<ContentPage
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:Prism.DI.Forms.Tests.Mocks.Views"
xmlns:prism="clr-namespace:Prism.Ioc;assembly=Prism.Forms"
xmlns:mvvm="clr-namespace:Prism.Mvvm;assembly=Prism.Forms"
xmlns:converters="using:Prism.Forms.Tests.Mocks.Converters"
Title="{Binding Title}"
x:Name="xamlViewMock"
x:Class="Prism.DI.Forms.Tests.Mocks.Views.XamlViewMock">
<ContentPage.Resources>
<ResourceDictionary>
<prism:ContainerProvider x:TypeArguments="converters:MockValueConverter" x:Key="mockValueConverter" />
</ResourceDictionary>
</ContentPage.Resources>
<StackLayout>
<local:PartialView mvvm:ViewModelLocator.AutowirePartialView="{x:Reference xamlViewMock}" />
<Entry x:Name="testEntry"
Text="{Binding Test,Converter={StaticResource mockValueConverter}}" />
</StackLayout>
</ContentPage>
如果您需要遵循一些自定义命名方案,您只需调用:
ViewModelLocationProvider.Register<MyView, SomeViewModel>();
更新
Prism 8 将引入对区域导航的支持。因此,Prism 7.1 中引入的“局部视图”将被删除。您需要迁移才能使用区域。这很容易做到,尽管在如何将参数传递到区域方面会有一些根本性的差异。
推荐阅读
- python - 从 B 字符串中删除 A 字符串
- python - PyO3 中自定义结构的向量
- apache-kafka - 如果多个消费者在同一个消费者组下运行,消费者是否从副本分区消费?
- react-native - 我怎样才能看到来自服务器的实际错误(反应本机)?
- flutter - ExpansionTile - 如何折叠其他磁贴,按下时隐藏键盘
- php - 如何获取用户交互的日期之间的日期
- mysql - 如何对多个表进行 SQL 连接(FK 表有循环的结果共享 ID)
- ios - 在黑盒情况下处理丢失的 dSYM 文件
- apache-spark - 为什么 Pyspark 没有编码器
- r - 在条件之前和之后的行中添加包含数据的列