Xamarin.Forms "Picker" Binding Problem

Question

I've designed an application to collect data from users about their addresses (city and district / province). In my database I have two tables, one for cities and another for their corresponding districts. In my XF app, I'm using MVVM to connect to the database, I have two Pickers one for cities, one for districts, and I've populated data in the cities Picker in the constructor. When I choose a city the other picker is populated with the related districts, but when I choose a district, and for some reason, I get back to change the city, the districts Picker is never filled with any data.

Code for getting the GUID of the selected city, then calling the method for getting the regions

Method for getting the regions based on the city GUID

        private string CityGuide;  
        private Category selectedCity;  
        public Category SelectedCity  
        {  
            get => selectedCity;  
            set  
            {  
                SetValue(ref selectedCity, value);  
                CityGuide = selectedCity.cardGuide;  
                //App.Current.MainPage.DisplayAlert("Current City GUID", CityGuide, "OK!");  
                LoadRegions();  
            }  
        }  

private async Task LoadRegions()  
        {  
            (List<Category> regionsData, string regionsResponse) = await new   
             CategoriesJsonService().LoadRegionsByCity(Guid.Parse(CityGuide));  
            if (regionsResponse != "Success!")  
            {  
                //error message  
                await Rg.Plugins.Popup.Services.PopupNavigation.Instance.PushAsync(new MessageView("حدث خطأ اثناء عملية الاتصال بمزود البيانات"));  
                return;  
            }  
            Regions = regionsData;  
        }  

Answer 1

Hello,​

when I choose a district, and for some reason, I get back to change the city, the districts Picker is never filled with any data.

If you reselect the city, the district picker do not update, Am I right?

If so, please set ObservableCollection for your Regions property. Because ObservableCollection implement the INotifyPropertyChanged interface, when you update the ObservableCollection, picker's ItemsSource will be change at runtime.

And change your LoadRegions method like following code. when you get the new Rigons, clean it and add the new Rigons.

   public ObservableCollection<Category> Regions { get; set; } = new ObservableCollection<Category>();  
           private async Task LoadRegions()  
           {  
               (List<Category> regionsData, string regionsResponse) = await new  
                CategoriesJsonService().LoadRegionsByCity(Guid.Parse(CityGuide));  
               if (regionsResponse != "Success!")  
               {  
                   //error message  
                   await Rg.Plugins.Popup.Services.PopupNavigation.Instance.PushAsync(new MessageView("حدث خطأ اثناء عملية الاتصال بمزود البيانات"));  
                   return;  
               }  
               Regions.Clear();  
               foreach (var item in regionsData)  
               {  
                   Regions.Add(item);  
               }  
             //  Regions = regionsData;  
           }  

Best Regards,

Leon Lu

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