Binding on a combobox and setting default value

Question

Hi

Does anyone have any example code they can share with me demonstrating binding a combobox through MVVM and setting the default value (IsSelected) to one of the comboboxitems? I can do the bind but cannot seem to set the default item.

Thanks

Answer 1

Hi,

Check the reply posted by me:

http://forums.silverlight.net/forums/p/135466/302729.aspx#302729

HTH

Answer 2

Hi,

Expose a propeerty in your VM following is the code

int _selectedvalue; 

public int SelectedValue

{

get { return _selectedValue; }set { _selectedValue = value; RaisePropertyChanged("SelectedValue"); }

}

 

In your constructor set selectedvalue = 1;(Or your default value)

In you XAML

<ComboBox

x:Name="cbo" Grid.Column="1" Grid.Row="4" ItemsSource="{Binding YourCollection}" DisplayMemberPath="Name" SelectedValuePath="CategoryId" SelectedValue="{Binding SelectedCategory, Mode=TwoWay}" HorizontalAlignment="Left" MaxWidth="250"/>

That would work :-)

HTH. Mark as answered if that helps

Regards.

Vidds

 

Answer 3

I have an example here: http://www.codeproject.com/KB/silverlight/SilverlightMVVMVideoPlay.aspx First, you MUST set the default value for SelectedIndex to -1. Then, I bind it like this: Then I simply change the value of SelectedVideoInListProperty to 0 to select the first item, or I search the SilverlightVideoList for the item I want and then set the SelectedVideoInListProperty to the index value of the item I want.

Answer 4

 

Binding Comobo:

LoadOperation loadPhysican = ctxClaim837.Load(ctxClaim837.FillPhysicanComboQuery("", "", "", "", false, "Select s.LName + Case IsNull(s.FName, '') When '' Then '' Else ', ' + s.FName End + Case IsNull(s.MName, '') When '' Then '' Else ' ' + s.MName End Provider, s.StaffId From emrStaff s, emrGroups g, emrUsers u Where g.GroupId = s.GroupId And s.StaffId = u.StaffId And (u.AcIsActive = 1 Or s.StaffId = '" + StaffId_PhyCmb + "') And g.IsDoctor = 1 Order By Provider"), OnFillPhysicanCombo, null);

private void OnFillPhysicanCombo(LoadOperation<ProviderDTO> operation)

{

if (operation != null)

{

if (operation.Entities.Count() > 0)

{

PhysicianComboBox = operation.Entities;

}

private void OnFillPhysicanCombo(LoadOperation<ProviderDTO> operation)

{

if (operation != null)

{

if (operation.Entities.Count() > 0)

{

PhysicianComboBox = operation.Entities;

}

SetPhysicianCmbIndex(StaffId_PhyCmb);

 

 

}

 

 

}

} 

Setting ComoboBox :

SetPhysicianCmbIndex( PhysicianId)

{

var SelectedItems = PhysicianComboBox.Where(p => p.StaffId == PhysicianId).ToList(); if (SelectedItems!=null) { if (SelectedItems.Count>0) PhysicianSelectedIndex = PhysicianComboBox.ToList().IndexOf(SelectedItems[0]); }

}

Thanks,

Ramesh

Answer 5

I am having a lot of trouble getting Vidds's suggestion to work: It seems he doesn't use the SelectedValue anywhere in the XAML. 

Does anybody have a working project visualizing how you can load a combobox, bind it, and selecting a specific item in the combobox to be the default value?

Answer 6

Hi Tricia,

I have selectedvalue in the XAML

<ComboBox  x:Name="cbo" Grid.Column="1" Grid.Row="4" ItemsSource="{Binding YourCollection}" DisplayMemberPath="Name" SelectedValuePath="CategoryId" SelectedValue="{Binding SelectedCategory, Mode=TwoWay}" HorizontalAlignment="Left" MaxWidth="250"/>

What the issue you are facing. Let us know.

HTH. Mark as answered if that helps :-)

Regards,

Vidds

 

 

Answer 7

Hi Vidds

Thanks for the reply :) 

I just assumed that the SelectedValue should be binded to the xaml, because in my case, setting the SelectedValue property to 1 in the constructor doesn't make much of a difference. But I am surely doing something wrong, but I really don't know what. 

Here's my combobox (sorry for the long names): 

  <ComboBox x:Name="AllQuestionnaire"
                                  ItemsSource="{Binding GroupQuestionnaireCB, Mode=TwoWay}"
                                  SelectedValue="{Binding SelectedGroupQuestionnaireCB, Mode=TwoWay}"
                                  DisplayMemberPath="GroupQuestionnaireName"
                                  SelectedValuePath="GroupQuestionnaireID" />
                                  
                                  

In my ViewModel I define the properties for GroupQuestionnaireCB and SelectedGroupQuestionaireCB. It is of tye GroupQUestionnaire, which I have defined in my Model  

   private ObservableCollection<GroupQuestionnaire> groupQuestionnaireCB;
        public ObservableCollection<GroupQuestionnaire> GroupQuestionnaireCB
        {
            get {
                 return groupQuestionnaireCB;  
            }
            set {
                groupQuestionnaireCB = value;
            RaisePropertyChanged("GroupQuestionnaireCB");
            }
        }

        private int selectedGroupQuestionnaireCB;
        public int SelectedGroupQuestionnaireCB 
        {
            get {
             
               return selectedGroupQuestionnaireCB;
            }
            set { selectedGroupQuestionnaireCB = value;
        RaisePropertyChanged("SelectedGroupQuestionnaireCB");
           
            }
        }

So, in my Constructor, I call the webservice and load the combobox, like this: 

   public MyConstructor()
        {
int UID = 8; //example         

            WebService = new Service1Client();
       
            WebService.GetGroupQuestionnaireCompleted += new EventHandler<GetParentQuestionnaireCompletedEventArgs>(WebService_GetParentQuestionnaireCompleted);
            WebService.GetGroupQuestionnaireAsync(UID);
        }
    public void  WebService_GetGroupQuestionnaireCompleted(object sender, GetGroupQuestionnaireCompletedEventArgs e)
            {
                GroupQuestionnaireCB = e.Result;
             }

So, I have defined the SelectedValue property as you proposed, and then I tried setting SelectedValue=1 both in the constructor, and in the method just above, where I populate the combobox. 

The thing is, I can easily set the SelectedGroupQuestionnaire to whatever I want, but it doesn't change the fact, that although it has that value, the combobox isn't visually updated, ie. it still shows an empty item when loaded. 

Does it make sense, that it doesn't work? 

Thanks :) 

Answer 8

Oh, I found out what the problem was. 

When you bind the combobox to the result of a WebService call, I have to set the selected value inside the Completed method... 

 public void  WebService_GetGroupQuestionnaireCompleted(object sender, GetGroupQuestionnaireCompletedEventArgs e)
            {
                GroupQuestionnaireCB = e.Result;
                SelectedGroupQuestionnaireCB = 1; //example
             }

So far I had SelectedGroupQuestionnaireCB after calling the Async method.. which of course doesn't make sense, because when you reach that it's very likely that the data has not yet been populated into the combobox...