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

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.