How to display default text "--Select Team --" in combo box on pageload in WPF?

Question

Hi,

In a WPF app, in MVP app

I have a combo box,for which I display the data fetched from Database. Before the items added to the Combo box, I want to display the default text such as " -- Select Team --" , so that on pageload it displays and on selecting it the text should be cleared and the items should be displayed.

Selecting data from DB is happening. I need to display the default text until the user selects an item from combo box.

Please guide me

Thanks

Ramm

Answer 1

comboBox1.Items.Insert(0, "**Select**");

Answer 2

I dont know if it's directly supported but you could overlay the combo with a label and set it to hidden if the selection isn't null.

eg.

<Grid>
   <ComboBox Text="Test" Height="23" SelectionChanged="comboBox1_SelectionChanged" Name="comboBox1" VerticalAlignment="Top" ItemsSource="{Binding Source=ABCD}"  />
   <TextBlock IsHitTestVisible="False" Margin="10,5,0,0" Name="txtSelectTeam" Foreground="Gray" Text="Select Team ..."></TextBlock>
</Grid>

Then in the selection changed handler ...

private void comboBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    txtSelectTeam.Visibility = comboBox1.SelectedItem == null ? Visibility.Visible : Visibility.Hidden;
}

Answer 3

Not best practice..but works fine...

<ComboBox GotFocus="Focused"  x:Name="combobox1" HorizontalAlignment="Left" Margin="8,29,0,0" VerticalAlignment="Top" Width="128" Height="117"/>

Code behind

public partial class MainWindow : Window
{
    bool clearonce = true;
    bool fillonce = true;
 public MainWindow()
 {
  this.InitializeComponent();          
        combobox1.Items.Insert(0, " -- Select Team --");
        combobox1.SelectedIndex = 0;
 }

    private void Focused(object sender, RoutedEventArgs e)
    {
            if(clearonce)
            {
                combobox1.Items.Clear();
                clearonce = false;
            }
            if (fillonce)
            {
              //fill the combobox items here 
                for (int i = 0; i < 10; i++)
                {
                    combobox1.Items.Insert(i, i);
                }
                fillonce = false;
            }           
    }
}

Answer 4

Not tried it with combo boxes but this has worked for me with other controls...

AgreedTrap blogpost

He uses the adorner layer here to display a watermark.

Answer 5

Set IsEditable=True on the Combobox element. This will display the Text property of the Combobox

Answer 6

You can do this without any code behind by using a IValueConverter.

<Grid>
   <ComboBox
       x:Name="comboBox1"
       ItemsSource="{Binding MyItemSource}"  />
   <TextBlock
       Visibility="{Binding SelectedItem, ElementName=comboBox1, Converter={StaticResource NullToVisibilityConverter}}"
       IsHitTestVisible="False"
       Text="... Select Team ..." />
</Grid>

Here you have the converter class that you can re-use.

public class NullToVisibilityConverter : IValueConverter
{
    #region Implementation of IValueConverter

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value == null ? Visibility.Visible : Visibility.Collapsed;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }

    #endregion
}

And finally, you need to declare your converter in a resource section.

<Converters:NullToVisibilityConverter x:Key="NullToVisibilityConverter" />

Where Converters is the place you have placed the converter class. An example is:

xmlns:Converters="clr-namespace:MyProject.Resources.Converters"

The very nice thing about this approach is no repetition of code in your code behind.

Answer 7

I like Tri Q's answer, but those value converters are a pain to use. PaulB did it with an event handler, but that's also unnecessary. Here's a pure XAML solution:

<ContentControl Content="{Binding YourChoices}">
<ContentControl.ContentTemplate>
    <DataTemplate>
        <Grid>
            <ComboBox x:Name="cb" ItemsSource="{Binding}"/>
            <TextBlock x:Name="tb" Text="Select Something" IsHitTestVisible="False" Visibility="Hidden"/>
        </Grid>
        <DataTemplate.Triggers>
            <Trigger SourceName="cb" Property="SelectedItem" Value="{x:Null}">
                <Setter TargetName="tb" Property="Visibility" Value="Visible"/>
            </Trigger>
        </DataTemplate.Triggers>
    </DataTemplate>
</ContentControl.ContentTemplate> </ContentControl>