NullToBoolValueConverter for WPF

  You can enable or disable WPF elements based on if they are null or not. This is not supported, but you can create a simple value converter.

  /// <summary>
  /// Converts null to boolean.
  /// </summary>
  /// <remarks>
  /// If parameter is not specified or specified with null:
  /// if passed value is null then true is returned, otherwise false.
  /// If parameter is specified then inversion is done:
  /// if passed value is null then false is returned, otherwise true.
  /// </remarks>
  [ValueConversion(typeof(object), typeof(bool))]
  public class NullToBoolValueConverter : IValueConverter
  {
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
      bool result = value == null ? true : false;
      if (parameter != null)
        return !result;
      return result;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
      return value;
    }
  }


  This value converter allows me to bind to any property taking a boolean argument with the following syntax in XAML.

<local:NullToBoolValueConverter x:Key="NullToBoolValueConverter"/>

<ComboBox.IsEnabled>
  <Binding ElementName="TetsComboBox" Path="SelectedItem" Converter="{StaticResource NullToBoolValueConverter}" ConverterParameter="true" />
</ComboBox.IsEnabled>


WPF show or hide element based on CheckBox

  Today I had to do the task for showing or hiding elements based the value of a checkbox. In WinForms 2.0 for this purpose it was necessary to subscribe to event CheckedChanged and in his handler write the code:

private void myCheckBox_CheckedChanged(object sender, EventArgs e)
{
  myTextBox.Visible = myCheckBox.Checked;
}

  With the new Visibility Enum in WPF, this becomes a bit trickier. To accomplish this, you can use converter BooleanToVisibilityConverter that accept a boolean value and return a visibility value. Now we can cleanly show or hide an element based on a checkbox using just XAML code. The XAML code to use this is below:

<Window

  x:Class="MyTest.XamlOnly"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Title="XamlOnly" Height="300" Width="300">

  <Window.Resources>
    <BooleanToVisibilityConverter x:Key="BoolToVisConverter" />
  </Window.Resources>

  <StackPanel Orientation="Vertical">
    <CheckBox Content="Check to show text box below me" Name="checkViewTextBox"/>
    <TextBox Text="only seen when above checkbox is checked" Visibility="{Binding Path=IsChecked, ElementName=checkViewTextBox, Converter={StaticResource BoolToVisConverter}}"/>
  </StackPanel>

</Window>