Answers

• JohnHardman GBUniversity admin

  November 2020 edited November 2020

  @xama12

  Make the BindingMode for SelectedItem TwoWay

  0
• xama12 Member ✭✭

  November 2020

  @JohnHardman

  SelectedItem="{Binding SelectedItem, Mode=TwoWay}"
  Tried it, does not work.

  0
• JohnHardman GBUniversity admin

  November 2020

  @xama12 said:
  @JohnHardman

  SelectedItem="{Binding SelectedItem, Mode=TwoWay}"
  Tried it, does not work.

  Show the full XAML and C#

  0
• xama12 Member ✭✭

  November 2020

  Full code:

  MainPage.xml

  <ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
               xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
               x:Class="example_.MainPage">
      <StackLayout>
          <Label Text="Test project for showing the problem with the picker"/>
          <Picker ItemsSource="{Binding TeamListe}" SelectedItem="{Binding SelectedItem, Mode=TwoWay}" />
          <Button Text="Test: Change picker selecteditem" Clicked="Button_Clicked"/>
      </StackLayout>
  </ContentPage>
  

  MainPage.cs

  public partial class MainPage : ContentPage
      {
          public MainPage()
          {
              InitializeComponent();
              BindingContext = new MainPageViewModel();
          }
  
          private void Button_Clicked(object sender, EventArgs e)
          {
              var viewModel = new MainPageViewModel();
              viewModel.SelectedItem = "Two";
          }
      }
  

  MainPageViewModel.cs

  class MainPageViewModel : BaseViewModel
      {
          public MainPageViewModel()
          {
              if (_TeamListe == null)
              {
                  TeamListe = new ObservableCollection<string>() { "One", "Two", "Three" };
                  SelectedItem = "One";
              }
          }
  
          static ObservableCollection<string> _TeamListe;
          public ObservableCollection<string> TeamListe
          {
              get { return _TeamListe; }
              set
              {
                  if (_TeamListe == null)
                  {
                      _TeamListe = value;
                  }
                  else
                  {
                      _TeamListe.Clear();
                      foreach (var item in value)
                      {
                          _TeamListe.Add(item);
                      }
                  }
                  OnPropertyChanged();
              }
          }
  
          static string _SelectedItem;
          public string SelectedItem
          {
              get { return _SelectedItem; }
              set
              {
                  _SelectedItem = value;
                  OnPropertyChanged("SelectedItem");
              }
          }
      }
  

  BaseviewModel.cs

  class BaseViewModel : INotifyPropertyChanged
      {
          protected BaseViewModel()
          {
          }
  
          public event PropertyChangedEventHandler PropertyChanged;
  
          protected virtual void OnPropertyChanged(
          [CallerMemberName] string propertyName = null)
          {
              PropertyChanged?.Invoke(this,
              new PropertyChangedEventArgs(propertyName));
          }
      }
  

  0
• JohnHardman GBUniversity admin

  November 2020

  @xama12 said:

          public MainPage()
          {
              InitializeComponent();
              BindingContext = new MainPageViewModel();
          }
  
          private void Button_Clicked(object sender, EventArgs e)
          {
              var viewModel = new MainPageViewModel();
              viewModel.SelectedItem = "Two";
          }
      }
  

  In your Clicked handler, you are instantiating a new view model instead of setting the SelectedItem of your existing view model.

  0
• xama12 Member ✭✭

  November 2020

  How do I access the current?

  0
• JohnHardman GBUniversity admin

  November 2020 Accepted Answer

  @xama12 said:
  How do I access the current?

  ((MainPageViewModel) BindingContext).SelectedItem = "Two";

  1