如何从ViewModel Xamarin表单访问工具栏项 [英] How to access toolbar items from ViewModel Xamarin forms

问题描述

我尝试在 viewmodel 的工具栏项中设置填充 我有一个名为IToolbarItemBadgeService

I tried to set padge in toolbar item from viewmodel I have interface called IToolbarItemBadgeService

public interface IToolbarItemBadgeService
    {
        void SetBadge(Page page, ToolbarItem item, string value, Color backgroundColor, Color textColor);
    }

我想在工具栏项中设置徽章，我在注册界面后使用了此代码，但是会引发异常

I want to set badge in toolbar item i used this code after i Register the interface but it throw exception

            private IToolbarItemBadgeService _toolbarItemBadge;

和构造函数

  public MainTabPageViewModel(IToolbarItemBadgeService toolbarItemBadge)
        {
            _toolbarItemBadge = toolbarItemBadge;
            _toolbarItemBadge.SetBadge(MainTabPage.Main,MainTabPage.Main.ToolbarItems.FirstOrDefault() , $"{BaseService.CartCounter}", Color.Orange, Color.White);
        }

抛出

异常:

Unity.Exceptions.ResolutionFailedException:解决方法 依赖关系失败，类型='System.Object'，名称='MainTabPage'. 发生以下异常:调用构造函数 LGMobileApp.Views.MainTabPage().例外是: ResolutionFailedException-解决依赖关系失败，键入 ='LGMobileApp.ViewModels.MainTabPageViewModel'，名称='(无)'.发生以下异常:调用构造函数 LGMobileApp.ViewModels.MainTabPageViewModel(Prism.Navigation.INavigationService navigationService，LGMobileApp.Helpers.IToolbarItemBadgeService toolbarItemBadge).异常是:NullReferenceException-对象 引用未设置为对象的实例.

Unity.Exceptions.ResolutionFailedException: Resolution of the dependency failed, type = 'System.Object', name = 'MainTabPage'. Exception occurred while: Calling constructor LGMobileApp.Views.MainTabPage(). Exception is: ResolutionFailedException - Resolution of the dependency failed, type = 'LGMobileApp.ViewModels.MainTabPageViewModel', name = '(none)'. Exception occurred while: Calling constructor LGMobileApp.ViewModels.MainTabPageViewModel(Prism.Navigation.INavigationService navigationService, LGMobileApp.Helpers.IToolbarItemBadgeService toolbarItemBadge). Exception is: NullReferenceException - Object reference not set to an instance of an object.

推荐答案

从异常中您可以看到您的服务未注册且无法解析.

From exception you can see that your service is not registred and it can not be resolved.

您需要注册IToolbarItemBadgeService接口，并在RegisterTypes方法中的App.cs内部实现.

You will need to register your IToolbarItemBadgeService interface, with implemenation inside of App.cs in RegisterTypes method.

类似这样的东西:

protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
      containerRegistry.Register<IToolbarItemBadgeService, ToolbarItemBadgeService>();
      // .. Other registration code
}

此后，您将能够使用注入到MainTabPageViewModel中的IToolbarItemBadgeService.

After this, you will be able to use IToolbarItemBadgeService which is injected in your MainTabPageViewModel.

祝您编程愉快！

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