Updating content between tabs binded by Preference

Question

I am using a tabbed app and I have a button on one tab, when the user clicks then it increments a Preference and I want to update its value on another tab. I tried to experiment with MVVM but I couldnt figure it out.

  public partial class Page1View: ContentPage
    {
        public Page1View()
        {
            InitializeComponent();
        }

        private void Button_Clicked(object sender, EventArgs e)
        {
            Preferences.Set("Total", Preferences.Get("Total", 0)+1);
        }
    }


public class Page2ViewModule : INotifyPropertyChanged
    {
        public int Total
        {
            get => Preferences.Get(nameof(Total), 0);
            set
            {
                if (Preferences.Get(nameof(Total),0) == value)
                    return;
                Preferences.Set(nameof(Total), value);
                OnPropertyChanged(nameof(Total));
            }
        }
        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged(string propertyName)
        {
            var changed = PropertyChanged;
            if (changed != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }

Answer 1

Hello,

Welcome to Microsoft Q&A!

@mrizoiwe98

You update the value with Preferences , but this will not trigger the change notify of Property Total in Page2ViewModule.

Total does not update , so the Label(or something else) does not update .

We should take a way to tell Total it should be changed after button clicking .

Here I suggest you use Messaging Center , I've mentioned it in this thread .

Here we just move the messaging center into Set method of the property .

   set  
   {  
        MessagingCenter.Subscribe<object>(this, "Hi", (o) => {                
                  OnPropertyChanged(nameof(Total));  
         });                          
   }  

If you have any question please let me know .

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