CODEWITHSUNDEEP
xamarinxamarin.forms
Vivendi
Vivendi

Reputation: 20997

Set initial value for Picker in ViewModel in Xamarin

Inside my Xamarin application I have added a Picker control to a page. The setup of that Picker looks like this in xaml:

<controls:ExtendedPicker x:Name="GenderPicker" Style="{StaticResource PickerControl}" Margin="0,0,0,20"
     ItemsSource="{Binding GenderItems}" 
     ItemDisplayBinding="{Binding Name}" 
     SelectedItem="{Binding Gender, Mode=TwoWay}" />

In my ViewModel I have this code to populate the picker with some values:

public class GenderItem
{
    public string Name { get; set; }
}

public class RegisterViewModel : BaseViewModel
{
    private DateTime _birthdate;
    public DateTime Birthdate { get => _birthdate; set => SetProperty(ref _birthdate, value); }

    public GenderItem Gender { get => _gender; set => SetProperty(ref _gender, value); }
    public List<GenderItem> GenderItems { get; set; } = new List<GenderItem>
    {
        new GenderItem { Naam = "Male" },
        new GenderItem { Naam = "Female" },
        new GenderItem { Naam = "Confused" }
    };

    public RegisterViewModel()
    {
        // This doesn't work
        Gender = new GenderItem { Naam = "Female" };

        // This works
        Birthdate = DateTime.Today.AddYears(-40);
    }
}

From within the constructor I try to set a default selected value for the Picker control. But for some reason the value isn't selected in the Picker.

I also set a datetime property with a value and I do see that this value is picked up by the Date control.

Why isn't this working for the Picker control? What can I do to make this work?

SetProperty method

The SetProperty method lives inside my BaseViewModel class. You get this with every new Xamarin project.

    public class BaseViewModel : INotifyPropertyChanged
    {
        public IDataStore<Item> DataStore => DependencyService.Get<IDataStore<Item>>();

        bool _isBusy = false;
        public bool IsBusy
        {
            get => _isBusy;
            set => SetProperty(ref _isBusy, value);
        }

        string _title = string.Empty;
        public string Title
        {
            get => _title;
            set => SetProperty(ref _title, value);
        }

        protected bool SetProperty<T>(ref T backingStore, T value,
            [CallerMemberName] string propertyName = "",
            Action onChanged = null)
        {
            if (EqualityComparer<T>.Default.Equals(backingStore, value))
                return false;

            backingStore = value;
            onChanged?.Invoke();
            OnPropertyChanged(propertyName);
            return true;
        }

        #region INotifyPropertyChanged
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
        {
            var changed = PropertyChanged;
            if (changed == null)
                return;

            changed.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
        #endregion
    }

Upvotes: 0

Views: 235

Answers (1)

Jason
Jason

Reputation: 89082

Gender needs to be an element in GenderItems. Right now you are creating a new object that has the same value as an item in GenderItems, but it is not the same object

Upvotes: 1

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