Programmatically set ComboBox SelectedItem in WPF (3.5sp1)

Question

I have been confused while setting SelectedItem programmaticaly in wpf applications with Net Framework 3.5 sp1 installed. I have carefully read about hundred posts \topics but still confused(( My xaml:

 <ComboBox name="cbTheme">
    <ComboBoxItem>Sunrise theme</ComboBoxItem>
    <ComboBoxItem>Sunset theme</ComboBoxItem> 
 </ComboBox>

If I add IsSelected="True" property in one of the items - it's dosn't sets this item selected. WHY ? And i was try different in code and still can't set selected item:

cbTheme.SelectedItem=cbTheme.Items.GetItemAt(1); //dosn't work
cbTheme.Text = "Sunrise theme"; //dosn't work
cbTheme.Text = cbTheme.Items.GetItemAt(1).ToString();//dosn't work
cbTheme.SelectedValue = ...//dosn't work
cbTheme.SelectedValuePath = .. //dosn't work
//and even this dosn't work:
ComboBoxItem selcbi = (ComboBoxItem)cbTheme.Items.GetItemAt(1);//or selcbi = new ComboBoxItem
cbTheme.SelectedItem = selcbi;

The SelectedItem is not readonly property, so why it wan't work? I think thats should be a Microsoft's problems, not my. Or I have missed something??? I have try playing with ListBox, and all work fine with same code, I can set selections, get selections and so on.... So what can I do with ComboBox ? Maybe some tricks ???

Answer 1

To select any item in the ComboBox and to set it as default item selected just use the below line:

combobox.SelectedIndex = 0; //index should be the index of item which you want to be selected

Answer 2

If i add the combobox and items programmatically, this works for me:

ComboBox newCombo = new ComboBox();

ComboBoxItem newitem = new ComboBoxItem();
newitem.Content = "test 1";
newCombo.Items.Add(newitem);
newitem = new ComboBoxItem();
newitem.Content = "test 2";
newCombo.Items.Add(newitem);
newitem = new ComboBoxItem();
newitem.Content = "test 3";
newCombo.Items.Add(newitem);

newCombo.SelectedItem =  ((ComboBoxItem)newCombo.Items[1]);
newCombo.Text = ((ComboBoxItem)newCombo.Items[1]).Content.ToString();

newStack.Children.Add(newCombo);

It also works if it set the ItemSource property programmatically, then set the text to the selected value.

Answer 3

Create a public property in your viewmodel for the theme list and one for the selected item:

    private IEnumerable<string> _themeList;
    public IEnumerable<string> ThemeList
    {
        get { return _themeList; }
        set
        {
            _themeList = value;
            PropertyChangedEvent.Notify(this, "ThemeList");
        }
    }
    private string _selectedItem;
    public string SelectedItem
    {
        get { return _selectedItem; }
        set
        {
            _selectedItem = value;
            PropertyChangedEvent.Notify(this,"SelectedItem");
        }            
    }

bind your combobox in xaml to the properties like this:

    <ComboBox 
        Name="cbTheme" 
        ItemsSource="{Binding ThemeList}"      
        SelectedItem="{Binding SelectedItem}">
    </ComboBox>

now all you do is add items to the ThemeList to populate the combobox. To select an item in the list, set the selected property to the text of the item you want selected like this:

    var tmpList = new List<string>();
    tmpList.Add("Sunrise theme");
    tmpList.Add("Sunset theme");

    _viewModel.ThemeList = tmpList;
    _viewModel.SelectedItem = "Sunset theme";

or try setting the selected item to the string value of the item you want selected in your own code if you want to use the code you currently have - not sure if it will work but you can try.

Answer 4

If you know the index of the item you want to set, in this case it looks like you are trying to set index 1, you simply do:

cbTheme.SelectedIndex = 1;

I found that when you don't know the index, that's when you have the real issue. I know this goes beyond the original question, but for Googlers on that count that want to know how to set the item when the index isn't known but the value you want to display IS known, if you are filling your dropdown with an ItemSource from a DataTable, for example, you can get that index by doing this:

int matchedIndex = 0;
if (dt != null & dt.Rows != null)
{
    if (dt.Rows.Count > 0)
    {
        foreach (DataRow dr in dt.Rows)
        {
            string myRowValue = dr["SOME_COLUMN"] != null ? dr["SOME_COLUMN"].ToString() : String.Empty;
            if (myRowValue == "Value I Want To Set")
                break;
            else
                matchedIndex++;
        }
     }
 }

And then you do simply do cbTheme.SelectedIndex = matchedIndex;.

A similar iteration of ComboBoxItem items instead of DataRow rows could yield a similar result, if the ComboBox was filled how the OP shows, instead.

Answer 5

Is the ComboBox data bound?

If so you are probably better to do it through Binding rather than code ....

See this question ... WPF ListView Programmatically Select Item

Maybe create a new SelectableObject {Text = "Abc Theme", IsCurrentlySelected = True} Bind a collection of SelectableObjects to the ComboBox.

Essentially setting the IsCurrentlySelected property in the model and having UI update from the Model.

Answer 6

Acording Answer 4

If you already add the Items in the Item source. Fire the PropertyChangedEvent of the selectet Value.

tmpList.Add("Sunrise theme"); 
    tmpList.Add("Sunset theme");
    PropertyChangedEvent.Notify(this,"SelectedItem");