WPF Bind Textbox IsEnabled to Listbox SelectedItem

Question

Hi everybody!

Using MVVM style i succefully bound an ObservableCollection to a listbox, showing up the values as radiobuttons. The control behaves exactly as expected.

Now i have an issue regarding some textboxes bound to this listbox: i want whenever the SelectedItem in the listbox is equal to a specific value (e.g. 'ValueForEnabled') the textboxes to be enabled otherwise they should be disabled.

I know i have to bind to SeletedItem of the listbox (named lbSource) but how exactly is this done?

I want something like this (Pseudo code):

<TextBox  ...

                      IsEnabled="{Binding ElementName=lbSource , Path=SelectedItem='ValueForEnabled' , Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" 
                      ...

/>

Thanks in advance

Answer 1

One way to skin this cat would be by converting the string (in the listbox) into a bool to pass into the IsEnabledProperty...

First, create a class that implements the IValueConverter interface, like:

public class StringToBoolConverter : IValueConverter
{
    #region IValueConverter Members

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value == null)
            return false;

        string keyword = value.ToString();
        if (keyword.Equals(parameter.ToString(), StringComparison.CurrentCultureIgnoreCase))
            return true;
        return false;
    }

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

    #endregion
}

Notice how you don't need to implement the ConvertBack method? That's because you only need to turn strings into bools, not vice-versa...

So you can declare an instance of your converter in the xaml, like

<Window
    ...
    xmlns:local="clr-namespace:WpfApplication1">

    <Window.Resources>
        <local:StringToBoolConverter x:Key="stringToBoolConverter" />
    </Window.Resources>

And finally, you can bind the TextBox to the ListBox's SelectedValue, like:

<TextBox Grid.Row="0" Width="90" Height="30" 
         IsEnabled="{Binding ElementName=lbSource, Path=SelectedValue, Converter={StaticResource stringToBoolConverter}, ConverterParameter=ValueForEnabled}">
</TextBox>

Note: This will only work if the ListBox contains strings, and you can be sure that the SelectedValue property is a string...

Answer 2

OK! Solved it (in another way) myself! For anyone who wants to know:

<TextBox 
...
usual property definitions
...
                      >
                <TextBox.Style>
                    <Style>
                        <Setter Property="TextBox.IsEnabled" Value="False"/>
                        <Style.Triggers>                              
                            <DataTrigger Binding="{Binding ElementName=lbSource , Path=SelectedItem}" Value="ValueForEnabled">
                                <Setter  Property="TextBox.IsEnabled" Value="true"/>
                            </DataTrigger>                           
                        </Style.Triggers>                       
                    </Style>                   
                </TextBox.Style>
            </TextBox>

Answer 3

Personally I think that if you're using MVVM then you should have the code remain in your ViewModel. so if your VM is like this:

public class MyViewModel
{
  public ObservableCollection<string> myColl {get;set;}
  public string SelectedString {get;set;}

  public bool IsEnabled
  {
     get { return SelectedString == "Desired string value";}
  }
}

You then would just bind the textboxes IsEnabled property to your IsEnabled property on your ViewModel

The reason I say this is your requirements may change as to when to have the textboxes enabled and if you do it this way you don't have to touch your view(where code/logic should not reside)

So now you do this in your view and thats it

<TextBox IsEnabled={Binding IsEnabled} Text={Binding SelectedString}/>

Hope I understand your problem and that this helps