Question

I was trying to set the visiblity of a Grid from code behind.

grdStopTimeOut.Visibility = Windows.Visibility.Visible

I have declared this grid in XAML and have set the visiblity to Visible.

<Grid Name="grdTimeTStopCondition"  Visibility="Hidden" Margin="0,29,0,-6">

Somehow when the application runs the grid is coming as nothing and the exceptions is thrown.
Anybody have any idea why it is happening??

XAML File

<Page x:Class="Page1"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
  xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
  mc:Ignorable="d" 
  d:DesignHeight="300" d:DesignWidth="300"
  Title="Page1">
<Grid>
    <ComboBox Height="23" HorizontalAlignment="Left"  Name="cmbStopConditions" VerticalAlignment="Top" Width="86" SelectedIndex="0">
        <ComboBoxItem Content="Expression"></ComboBoxItem>
        <ComboBoxItem Content="Manual"></ComboBoxItem>
    </ComboBox>
    <Grid Name="grdStopTimeOut" Visibility="Visible" >
        <Label Content="Timeout" Height="28" HorizontalAlignment="Left"  Name="lblTimeout_stopcond" VerticalAlignment="Top" Margin="0,29,0,0" />
        <TextBox Height="23" HorizontalAlignment="Left"  Name="txtStopTimeout" VerticalAlignment="Top" Width="30" Margin="60,29,0,0" />
        <Label Content="secs" Height="28" HorizontalAlignment="Left"  Name="lblTimeoutSec_stopCond" VerticalAlignment="Top" Width="39" Margin="105,24,0,0" />
    </Grid>
</Grid>
</Page>

CodeBehind

Class Page1 

Public Sub New()

    ' This call is required by the designer.
    InitializeComponent()

    ' Add any initialization after the InitializeComponent() call.

End Sub
Private Sub cmbStopConditions_SelectionChanged(ByVal sender As Object, ByVal e As System.Windows.Controls.SelectionChangedEventArgs) Handles cmbStopConditions.SelectionChanged
    Dim item As ComboBoxItem = TryCast(cmbStopConditions.SelectedItem, ComboBoxItem)
    If item IsNot Nothing Then
        If Convert.ToString(item.Content) = "Expression" Then
            grdStopTimeOut.Visibility = Windows.Visibility.Visible
        ElseIf Convert.ToString(item.Content) = "Manual" Then
            grdStopTimeOut.Visibility = Windows.Visibility.Hidden
        End If
    End If
End Sub

End Class

regards,

SKB

Answer 1

Edit: The handler can occur before the grid is initialized, so a null-check is in order.

Are you calling this before InitializeComponent? That for one would explain the lack of a reference because all the fields are hooked up with the named controls in that method.