Xamarin.Forms MVVM Light IDialogService ShowMessage抛出本机异常 [英] Xamarin.Forms MVVM Light IDialogService ShowMessage throwing native exception

问题描述

我最近开始使用MVVM Light，并且第一次使用IDialogService.

i recently started working with MVVM Light and just used the IDialogService for the first time.

我的ViewModelLocator

My ViewModelLocator

ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);

// Register the dialog service provided by mvvm light
SimpleIoc.Default.Register<IDialogService, DialogService>();

我的ViewModel

My ViewModel

private IRestService _restService;

public OrderViewModel (IDialogService dialogService )
{ 
   _dialogService = dialogService;
}

最后使用ShowMessage:

And finally using ShowMessage:

await _dialogService.ShowMessage("test", "test", "Ok", "Nop", (result) => { 
   if (result)
   {
      //...
   }
   else
   {
      //...
   }
});

导致此异常的原因:

Java.Lang.NullPointerException: Attempt to invoke virtual method 
'android.content.res.Resources$Theme android.content.Context.getTheme()'
on a null object reference 

有人可以告诉我怎么回事吗?

Can someone tell me whats going on ?

推荐答案

我认为问题是尚未设置当前活动.问题是，MvvmLight需要CurrentActivity属于ActivityBase类型.因此，我认为DialogService不能真正与Forms兼容，因为Forms要求Activity从FormsAppCompatActivity继承.那将构成一个很好的菱形继承，这是不可能的，因为C#不支持多重继承.

I think the problem is, that current activity has not been set. The problem is, that MvvmLight needs CurrentActivity to be of type ActivityBase. So i think the DialogService not really compatible with Forms, because Forms requires the Activity to inherit from FormsAppCompatActivity. That would make up a nice diamond shaped inheritance, which is not possible, because C# doesn't support multiple inheritance.

因此您可以使用ACR用户Daialog: https://www.nuget.org/packages /Acr.UserDialogs/

So you could use ACR User Daialogs: https://www.nuget.org/packages/Acr.UserDialogs/

请参见 https://github.com/aritchie/userdialogs #android-initialization-in-your-main-activity 进行设置.

您可以注册

SimpleIoc.Default.Register<IUserDialogs>(UserDialogs.Instance);

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