WPF Textbox is collapsed when the content string is a single digit - wpf

Question

I am working on an application that creates textboxes/combo boxes dynamically based on if there is a single replacement for a keyword, or multiple replacements, and adds them to a stackpanel. I have ran into an issue where if the string that is being populated into the textbox is a single digit, ie: "2" the textbox is collapsed. Here is the associated DependencyProperty and constructor for the view model:
#region Properties
public ObservableCollection<string> KeywordValueList
{
get { return (ObservableCollection<string>)GetValue(_KeywordValueListProperty); }
set { SetValue(_KeywordValueListProperty, value); }
}
private static readonly DependencyProperty _KeywordValueListProperty = DependencyProperty.Register("KeywordValueList",
typeof(ObservableCollection<string>),
typeof(KeywordControlViewModel),
new PropertyMetadata(null, null));
public string KeywordValue
{
get { return (string)GetValue(_KeywordValueProperty); }
set { SetValue(_KeywordValueProperty, value); }
}
private static readonly DependencyProperty _KeywordValueProperty = DependencyProperty.Register("KeywordValue",
typeof(string),
typeof(KeywordControlViewModel),
new PropertyMetadata(null, null));
#endregion
#region Constructors
public KeywordControlViewModel(string keyword, object keywordValue)
{
Keyword = keyword;
if (keywordValue is string)
{
KeywordValue = (string)keywordValue;
KeywordValueList = null;
}
else if (keywordValue is ICollection)
{
KeywordValue = null;
ObservableCollection<string> toSet = new ObservableCollection<string>(keywordValue as List<string>);
KeywordValueList = toSet;
}
else
{
KeywordValue = "-Not Set-";
KeywordValueList = null;
}
}
#endregion
This is the relevant portion of the xaml:
<Grid HorizontalAlignment="Stretch">
<Grid.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="../Styles/ControlsStyle.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Grid.Resources>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="180" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="30" />
<RowDefinition Height="25" />
</Grid.RowDefinitions>
<!-- Labels etc on Row 0, generating properly so omitting for space-->
<TextBox Name ="KeyWordTextBox"
Style="{StaticResource InputBoxStyle}"
Text="{Binding KeywordValue}"
Grid.Row="1"
Grid.Column="0"
Grid.ColumnSpan="3"
Visibility="{Binding KeywordValue, TargetNullValue=Hidden}">
<TextBox.ToolTip>
<Label Content="{Binding Keyword, StringFormat='Edit value for {0}'}" />
</TextBox.ToolTip>
</TextBox>
<ComboBox Name="KeyWordComboBox"
ItemsSource="{Binding KeywordValueList}"
Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="3" Visibility="{Binding KeywordValueList, TargetNullValue=Hidden}"/>
</Grid>
And the style:
<Style x:Key="InputBoxStyle" TargetType="TextBox">
<Setter Property="Margin" Value="0,0,5,0" />
<Setter Property="HorizontalAlignment" Value="Stretch" />
<Setter Property="Height" Value="20" />
</Style>
I have debugged quite a bit and found that if I change the single digit to either a single letter, string of more than one number, or string containing both it shows the textbox as expected. Also, the Visibility value for the textbox in the debugger shows Collapsed, not Hidden -- the TargetNullValue does not seem to be causing this. In fact the textbox does not show either if I change it to Visible. This only started happening when I added the option for a combobox, prior to that the textbox generated properly with a single digit.
Can anyone offer an idea why this may be happening?

Answer 1

I suppose that the code doesn't work because You are binding a string value (and ObservableCollection<string> value in case of combobox) to a Visibility property.
In order to hide controls on null value:
You can write a value converter similar to the one suggested here: https://stackoverflow.com/a/2123905/232530 (but just check if value parameter is null in the Convert method)
or
You can use triggers as suggested here: How to hide the empty TextBlock?.
Please let me know if You need help when using any of those solutions.