问题
As Prism said,
To obtain the INavigationService in your ViewModels simply ask for it as a constructor parameter
https://prismlibrary.github.io/docs/xamarin-forms/Navigation-Service.html#getting-the-navigation-service
like this:
public SpeakPageViewModel(INavigationService navigationService) : base(navigationService)
{
_navigationService = navigationService;
}
and I want to use ITextToSpeech interface as Prism sample :
public MainPageViewModel(ITextToSpeech textToSpeech)
{
_textToSpeech = textToSpeech;
SpeakCommand = new DelegateCommand(Speak);
}
https://prismlibrary.github.io/docs/xamarin-forms/Dependency-Service.html#use-the-service
The problem is: when add another parameter to the constructor, the navigation doesn't work.
public SpeakPageViewModel(ITextToSpeech textToSpeech, INavigationService navigationService) : base(navigationService)
{
_navigationService = navigationService;
_textToSpeech = textToSpeech;
}
project file : http://www.mediafire.com/file/nl6dx5c4mc3mg63/FirstPrismApp.rar
回答1:
Prism 7 changed this behavior as it is actually an anti-pattern to rely on a secondary container. You simply need to register your TextToSpeech service in the IPlatformInitializer like:
public class iOSInitializer : IPlatformInitializer
{
public void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.Register<ITextToSpeech, TextToSpeech_iOS>();
}
}
来源：https://stackoverflow.com/questions/50391145/prism-xamarin-forms-navigation-service-dependencyservice