Databinding works in Visual Studio 2013 but not actual app

Question

I have an app in which I only want to display the next TextBox only when the first one has something entered into it. I am using an IValueConverter to do this. Here is my IValueConverter and the relevant XAML:

Public Class HideValueVisibilityConverter : Implements IValueConverter
	Public Function Convert(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.Convert
		If parameter Is Nothing Then
			If value.ToString() = "0" Then Return Visibility.Collapsed Else Return Visibility.Visible
		Else
			If value.ToString() = parameter.ToString() Then Return Visibility.Collapsed Else Return Visibility.Visible
		End If
	End Function
	Public Function ConvertBack(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.ConvertBack
		Return value
	End Function
End Class

<TextBox Grid.Column="0" Grid.Row="2" Style="{StaticResource PlayerNameTextBoxStyle}" PlaceholderText="Player 1" TextChanged="Name_TextChanged"/>
<TextBox Grid.Column="1" Grid.Row="2" Style="{StaticResource CardCountTextBoxStyle}" TextChanged="CardCount_TextChanged"/>
<TextBox Grid.Column="0" Grid.Row="3" Style="{StaticResource PlayerNameTextBoxStyle}" PlaceholderText="Player 2" Visibility="{Binding Parent.Children[2].Text,RelativeSource={RelativeSource Mode=Self},Converter={StaticResource HideValueVisibility},ConverterParameter=''}" TextChanged="Name_TextChanged"/>
<TextBox Grid.Column="1" Grid.Row="3" Style="{StaticResource CardCountTextBoxStyle}" Visibility="{Binding Parent.Children[2].Text,RelativeSource={RelativeSource Mode=Self},Converter={StaticResource HideValueVisibility},ConverterParameter=''}" TextChanged="CardCount_TextChanged"/>

In Visual Studio 2013, the second set of TextBoxes are Visible/Collapsed like I want depending on the Text property of the first TextBox, but when I actually run the app it is displayed regardless of whether I have entered anything into the first TextBox. I would expect the Visibility of the second set of TextBoxes to change when I enter or remove text from the first TextBox. Am I doing something wrong? Why is Visual Studio 2013 showing it differently from the actual app? Any help would be appreciated. Thanks.

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Nathan Sokalski [e-mail] http://www.nathansokalski.com/

Answer 1

Hi, please try this minor change:

<TextBox Grid.Column="0" Grid.Row="2" Style="{StaticResource PlayerNameTextBoxStyle}" PlaceholderText="Player 1" TextChanged="Name_TextChanged"/>
<TextBox Name="tb" Grid.Column="1" Grid.Row="2" Style="{StaticResource CardCountTextBoxStyle}" TextChanged="CardCount_TextChanged" />
<TextBox Visibility="{Binding Text,ElementName=tb,Converter={StaticResource HideValueVisibility},ConverterParameter=0}" Grid.Column="0" Grid.Row="3" Style="{StaticResource PlayerNameTextBoxStyle}" PlaceholderText="Player 2"  TextChanged="Name_TextChanged"/>
<TextBox Visibility="{Binding Text,ElementName=tb,Converter={StaticResource HideValueVisibility},ConverterParameter=0}" Grid.Column="1" Grid.Row="3" Style="{StaticResource CardCountTextBoxStyle}"  TextChanged="CardCount_TextChanged"/>

Public Class HideValueVisibilityConverter : Implements IValueConverter
    Public Function Convert(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.Convert
        If parameter Is Nothing Then
            If value.ToString() = "0" Then Return Visibility.Collapsed Else Return Visibility.Visible
        Else
            If value.Length = parameter Then Return Visibility.Collapsed Else Return Visibility.Visible
        End If
    End Function
    Public Function ConvertBack(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.ConvertBack
        Return value
    End Function
End Class

Answer 2

That does not work, because it sets the Visibility based on whether or not the TextBox has a value of 0; I want it to be based on whether or not it has a value of "" (an empty string). But I may have figured out why it is not doing what I want; the ConverterParameter is being passed Nothing rather than a String. But if I cannot use ConverterParameter='' to pass a String, how do I pass it? Thanks.

---

Nathan Sokalski [e-mail] http://www.nathansokalski.com/

Answer 3

I was hoping I wouldn't need to resort to this so that I could reuse my existing IValueConverter, but I wrote a more specific IValueConverter for empty strings so that it doesn't need a parameter:

Public Class HideEmptyVisibilityConverter : Implements IValueConverter
	Public Function Convert(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.Convert
		If parameter IsNot Nothing AndAlso parameter.ToString().ToUpper() = "NOT" Then : Return If(Not String.IsNullOrWhiteSpace(value.ToString()), Visibility.Collapsed, Visibility.Visible)
		Else : Return If(String.IsNullOrWhiteSpace(value.ToString()), Visibility.Collapsed, Visibility.Visible)
		End If
	End Function
	Public Function ConvertBack(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.ConvertBack
		Return value
	End Function
End Class

This worked, so I guess I will need to use it for now. I would, however, still like to know how to pass an empty string as a ConverterParameter in XAML. Thanks.

---

Nathan Sokalski [e-mail] http://www.nathansokalski.com/

Answer 4

Hi,

If you want to pass an empty string as a ConverterParameter, you should convert the null to string. Some codes below:

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Grid.Resources>
            <local:HideValueVisibility x:Key="HideValueVisibility" />
        </Grid.Resources>
        <TextBox HorizontalAlignment="Left" Name="tb" Margin="478,124,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="258"/>
        <TextBox HorizontalAlignment="Left" Name="tb1" Margin="438,219,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="351" Visibility="{Binding Text,ElementName=tb,Converter={StaticResource HideValueVisibility},ConverterParameter=''}"/>

    </Grid>

Public NotInheritable Partial Class MainPage
	Inherits Page
	Public Sub New()
		Me.InitializeComponent()
	End Sub
	Public Shared Function NullToString(Value As Object) As String

		' Value.ToString() allows for Value being DBNull, but will also convert int, double, etc.
		Return If(Value Is Nothing, "", Value.ToString())

		' If this is not what you want then this form may suit you better, handles 'Null' and DBNull otherwise tries a straight cast
		' which will throw if Value isn't actually a string object.
		'return Value == null || Value == DBNull.Value ? "" : (string)Value;


	End Function
End Class


Public Class HideValueVisibility : Implements IValueConverter
    Public Function Convert(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.Convert
           If value.ToString() = MainPage.NullToString(parameter) Then
	Return Visibility.Collapsed
           Else
	Return Visibility.Visible
          End If
       
    End Function
    Public Function ConvertBack(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.ConvertBack
        Return value
    End Function
End Class

Best Wishes!

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