CODEWITHSUNDEEP
wpfmvvm
Stacked
Stacked

Reputation: 7336

WPF MVVM updating property in viewmodel when something changes in other viewmodel

I need to update the Language property in MyVM1 and MyVM2 when the Language property changes in LanguageVM (see image).

enter image description here

Upvotes: 1

Views: 551

Answers (2)

Jimmy
Jimmy

Reputation: 3274

I personally prefer interface based programming and readability of dependencies. See below

Code is not compiled or tested and only given to convey the idea.

Your viewmodels are "language aware". Create an interface for this functionality

public interface ILanguageAware
{
   void ChangeLanguage(string lang);
}

implement the interface

public class MyVM1:ILanguageAware
{
  public void ChangeLanguage(string lang)
  {
    //do the language change tasks
  }
}

Your provider can have the capability to keep the language aware objects

public interface ILanguageProvider
{
   void AddLanguageAwareObject(ILanguageAware langawareobj) ;

   void RemoveLanguageAwareObject(ILanguageAware langawareobj) ;
}

Your viewmodels can add themselves the language provider

public MyVM1:ILanguageAware
{
  ILanguageProvider _langprovider =null;

  public MyVM1(ILanguageProvider provider)
  {
    _langprovider = provider;
    _langprovider.AddLanguageAwareObject(this);
  }

}

Implement the provider

public class LanguageProvider:ILanguageProvider
{
  List<ILanguageAware> _langawarelist = new List<ILanguageAware>();

  void AddLanguageAwareObject(ILanguageAware langawareobj) 
  {
   _langawarelist .Add(langawareobj);
  }

  public void SetLanguage(string lang)
  {
  _langawarelist .foreach(x=>x.ChangeLanguage(lang);

  }    

}

Upvotes: 1

stukselbax
stukselbax

Reputation: 5935

You have a lot of approaches to accomplish this. You can define an event in your LanguageProvider class. If you can have only one LanguageProvider object, you can mark the event as static, so you do not need to pass reference to LanguageProvider to YoursVM classes.

public static class LanguageProvider
{
    private Language currentLanguage = Language.DefaultLanguage;
    public delegate void LanguageChangedEventHandler(object sender, LanguageChangedEventArgs e);

    public static event LanguageChangedEventHandler LanguageChanged;
    public static void SetLanguage(string langId)
    {
        var oldLang = currentLanguage;
        currentLanguage = new Language(langId);
        if (LanguageChangedEventHandler != null)
        {
            LanguageChangedEventHandler(null, new LanguageChangedEventArgs(oldLangId:oldLang, newLang:currentLanguage)); 
        }
    }         
}

And in your BaseVM base constructor:

public BaseVM()
{
    ...
    LanguageProvider.LanguageChanged += OnLanguageChanged;
    ...
}

private void OnLanguageChanged(object sender, LanguageChangedEventArgs e)
{
    this.Language = e.NewValue;
}

Upvotes: 0

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