WPF MVVM ComboBox SelectedItem or SelectedValue not working

Question

Update  After a bit of investigating   What seems to be the issue is that the SelectedValue SelectedItem is occurring before the Item source is finished loading   If I sit in a break point and wait a few seconds it works as expected   Don t know how I m going to get around this one   End Update  I have an application using in WPF using MVVM with a ComboBox   Below is the ViewModel Example   The issue I m having is when we leave our page and migrate back the ComboBox is not selecting the current Value that is selected   View Model  public class MyViewModel        private MyObject  selectedObject       private Collection lt Object2 gt   objects       private IModel  model        public MyViewModel IModel model                  model   model            objects    model GetObjects               public Collection lt MyObject gt  Objects                get                          return  objects                      private set                           objects   value                          public MyObject SelectedObject                  get                           return  selectedObject                        set                             selectedObject   value                           For the sake of this example lets say MyObject has two properties  Text and Id    My XAML for the ComboBox looks like this   XAML   lt ComboBox Name  MyComboBox  Height  23   Width  auto       SelectedItem   Binding Path SelectedObject Mode TwoWay        ItemsSource   Binding Objects       DisplayMemberPath  Text      SelectedValuePath  Id  gt    No matter which way I configure this when I come back to the page and the object is reassembled the ComboBox will not select the value   The object is returning the correct object via the get in the property though   I m not sure if this is just an issue with the way the ComboBox and MVVM pattern works   The text box binding we are doing works correctly

User · Answer

I was fighting with this issue for a while   In my case I was using in complex type  List  as the Item Source and was using a KeyType as the selected value   On the load event  the KeyType was getting set to null   This caused everything to break   None of the sub elements would get updated when the key changed   It turned out that when I added a check to make sure the proposed value for KeyType was not null  everything worked as expected        region Property  SelectedKey        s Append string Format  SelectedKey    0      Environment NewLine  SelectedKey ToString           private KeyType  SelectedKey   new KeyType        public KeyType SelectedKey               get   return  SelectedKey            set                       if value    null                   if    SelectedKey Equals value                                          SelectedKey   value                      OnPropertyChanged  SelectedKey                                           endregion SelectedKey

User · Answer

Setting IsSynchronizedWithCurrentItem  True  worked for me

User · Answer

I have noticed this behavior before as well   I have noticed that the SelectedIndex property doesn t cause the same bug   If you can restructure your ViewModel to expose the index of the selected item  and bind to that  you should be good to go

User · Answer

I solved the problem by adding dispatcher in UserControl Loaded event   Dispatcher BeginInvoke DispatcherPriority Loaded  new Action      gt          combobox SelectedIndex   0

User · Answer

When leaving the current page  the CollectionView associated with the ItemsSource property of the ComboBox is purged  And because the ComboBox IsSyncronizedWithCurrent property is true by default  the SelectedItem and SelectedValue properties are reset  This seems to be an internal data type issue in the binding  As others suggested above  if you use SelectedValue instead by binding to an int property on the viewmodel  it will work  A shortcut for you would be to override the Equals operator on MyObject so that when comparing two MyObjects  the actual Id properties are compared   Another hint  If you do restructure your viewmodels and use SelectedValue  use it only when SelectedValuePath Id where Id is int  If using a string key  bind to the Text property of the ComboBox instead of SelectedValue

User · Answer

You need to put the ItemsSource property BEFORE the SelectedItem property  I came across a blog a few days ago mentioning the issue

User · Answer

IsSyncronizedWithCurrent False will make it work

User · Answer

I had this problem with a ComboBox displaying a list of colors   List lt Brush gt     Selecting a color was possible but it wasnt displayed when the selection closed  although the property was changed    The fix was overwriting the Equals object obj  method for the type selected in the ComboBox  Brush   which wasnt simple because Brush is sealed  So i wrote a class EqualityBrush containing a Brush and implementing Equals   public class EqualityBrush       public SolidColorBrush Brush   get  set         public override bool Equals object o                if  o is EqualityBrush                        SolidColorBrush b     EqualityBrush o  Brush              return b Color R    this Brush Color R  amp  amp  b Color G    this Brush Color G  amp  amp  b Color B    this Brush Color B                    else             return false            Using a List of my new EqualityBrush class instead of normal Brush class fixed the problem   My Combobox XAML looks like this    lt ComboBox ItemsSource   Binding BuerkertBrushes   SelectedItem   Binding Brush  Mode TwoWay   Width  40  gt       lt ComboBox Resources gt           lt DataTemplate DataType   x Type tree EqualityBrush   gt               lt Rectangle Width  20  Height  12  Fill   Binding Brush    gt           lt  DataTemplate gt       lt  ComboBox Resources gt   lt  ComboBox gt    Remember that my  Brush -Property in the ViewModel now has to be of Type EqualityBrush

User · Answer

The type of the SelectedValuePath and the SelectedValue must be EXACTLY the same   If for example the type of SelectedValuePath is Int16 and the type of the property that binds to SelectedValue is int it will not work   I spend hours to find that  and that s why I am answering here after so much time the question was asked  Maybe another poor guy like me with the same problem can see it

User · Answer

It could be the way you are applying the DataContext to the Page  In WPF  everytime you navigate to a Page everything gets re-initialized  constructor gets called  loaded methods  everything  so if you are setting your DataContext inside your View you will no doubt be blowing away that SelectedItem that the user selected  In order to avoid that use the KeepAlive property of your pages    lt Page KeepAlive  True      gt          lt  Page gt    This will result in only the Loaded event being fired when navigating back to a page you have already visited  So you will need to ensure that you are setting the DataContext on Initialize  either externally or within the constructor  rather than Load    However  this will only work for that instance of the Page  If you navigate to a new instance of that page it constructor will be called again

User · Answer

I have had similar issues and it was solved by making sure I was implementing IEquatable properly   When the binding occurs  it is trying to see if the objects match so make sure you are properly implementing your equality checking

User · Answer

ComboBox SelectionBoxItem ToString

User · Answer

I had the same problem  The thing is  The selected item doesnt know which object it should use from the collection  So you have to say to the selected item to use the item from the collection   public MyObject SelectedObject          get                   Objects find x   gt  x id     selectedObject id            return  selectedObject                set                     selectedObject   value               I hope this helps

User · Answer

I have a very simply answer for this problem  First add the following code to the View IsSynchronizedWithCurrentItem  True     Next when ever you assign a new object in the ViewModel to that Property SelectedObject should be saved to that Property and not the private member    The viewmodel Proptery should look like this      public Role SelectedObject                get   return object            set                       if  value    null                                if   object Equals value                                         object   value                      OnPropertyChanged      gt  SelectedObject                                                      This should fix the issue

User · Answer

Use Loaded event    private void cmb Loaded object sender  RoutedEventArgs e        if  cmb Items Count  gt  0  cmb SelectedIndex   0                It works for me

User · Answer

Have you tried implementing INotifyPropertyChanged in your viewmodel  and then raise the PropertyChanged event when the SelectedItem gets set   If this in itself doesn t fix it  then you will be able to manually raise the PropertyChanged event yourself when navigating back to the page  and that should be enough to get WPF to redraw itself and show the correct selected item

User · Answer

In this case  the selecteditem bind doesn t work  because the hash id of the objects are different   One possible solution is   Based on the selected item id  recover the object on the itemsource collection and set the selected item property to with it   Example    lt ctrls ComboBoxControlBase SelectedItem   Binding Path SelectedProfile  Mode TwoWay   ItemsSource   Binding Path Profiles  Mode OneWay   IsEditable  False  DisplayMemberPath  Name    gt    The Property binded to ItemSource is   public ObservableCollection lt Profile gt  Profiles      get   return this profiles       private set   profiles   value  RaisePropertyChanged  Profiles          The property binded to SelectedItem is   public Profile SelectedProfile        get   return selectedProfile        set               if  this SelectedUser    null                        this SelectedUser Profile   value               RaisePropertyChanged  SelectedProfile                            The recovery code is        Command  SelectionChanged        public void SelectionChanged User selectedUser                if  selectedUser    null                        if  selectedUser is User                                if  selectedUser Profile    null                                        this SelectedUser   selectedUser                      this selectedProfile   this Profiles Where p   gt  p Id    this SelectedUser Profile Id  FirstOrDefault                        MessageBroker Instance NotifyColleagues  ShowItemDetails                                                                   I hope it helps you  I spent a lot of my time searching for answers  but I couldn  t find

User · Answer

You can also bind your SelectedIndex to a property in your ViewModel and manipulate your SelectedItem that way            public int SelectedIndex                       get   return  selectedIndex                set                                selectedIndex   value                  OnPropertyChanged                                  And in your XAML    lt ComboBox SelectedIndex   Binding SelectedIndex Mode TwoWay        gt

[wpf] WPF MVVM ComboBox SelectedItem or SelectedValue not working

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