wpf UserControl, FindChild returns null

Question

I have a usercontrol where the xaml is as follows. Please see the VisualChild line in the cs file thats the problem. When I try to find the UserControl I keep a break point it is null and hence I cant find the textblock element. My VisualChild is the same code at this place. How can I find WPF controls by name or type? Please help.

XAML:

<UserControl Name="NFView" x:Class="AthenaIsolatedFeatures.ProximityAlerts.Views.NotificationView"
             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" 
             xmlns:local="clr-namespace:AthenaIsolatedFeatures.ProximityAlerts.Views"
             xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
             xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <UserControl.Resources>
        <DataTemplate x:Key="CustomNotificationTemplate">

            <Border Name="border" BorderBrush="Black" BorderThickness="1" MouseLeftButtonDown="Border_MouseLeftButtonDown">
                <!--<i:Interaction.Triggers>
                    <i:EventTrigger EventName="MouseDown">
                        <i:InvokeCommandAction Command="{Binding AlertClickCommand}" CommandParameter="{Binding}"></i:InvokeCommandAction>
                    </i:EventTrigger>
                </i:Interaction.Triggers>-->

                <DockPanel LastChildFill="True">

                    <StackPanel DockPanel.Dock="Top" Grid.Row="0" Background="Red">
                        <TextBlock Text="Proximity Alert" HorizontalAlignment="Left"></TextBlock>
                    </StackPanel>
                    <Grid Name="GRD2" Background="#FFB6C1" DockPanel.Dock="Bottom" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">

                        <Grid.RowDefinitions>
                            <RowDefinition Height="Auto"></RowDefinition>
                            <!--<RowDefinition Height="Auto"></RowDefinition>-->
                            <RowDefinition Height="Auto"></RowDefinition>
                            <RowDefinition Height="Auto"></RowDefinition>

                        </Grid.RowDefinitions>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="Auto"></ColumnDefinition>
                            <ColumnDefinition Width="Auto"></ColumnDefinition>
                            <ColumnDefinition Width="Auto"></ColumnDefinition>

                        </Grid.ColumnDefinitions>

                        <Image Source="{Binding Source}" Grid.Row="0" Grid.Column="0" Grid.RowSpan="2" Margin="4,-25,0,0" Height="100" Width="65"></Image>

                        <TextBlock Grid.Row="0" Margin="25,5,0,0" Grid.Column="1" Text="{Binding AlertDescription}" FontSize="15" FontWeight="Bold"></TextBlock>
                        <!--<TextBlock Grid.Row="1" Grid.Column="1" Margin="7,1,0,0" Text="{Binding requestId}"></TextBlock>-->
                        <TextBlock Grid.Row="1" Margin="25,-28,0,0" Grid.Column="1" Text="{Binding requestId,StringFormat='Session: {0}'}"></TextBlock>
                        <TextBlock Grid.Row="0" Grid.Column="2" HorizontalAlignment="Right" Margin="39,5,0,0" Text="{Binding alertTimeStamp}"></TextBlock>
                        <TextBlock Grid.Row="2" Grid.Column="1" Grid.ColumnSpan="2" Margin="25,-30,0,0" Text="{Binding AlertText}"></TextBlock>
                        <TextBlock Name="tblAlertId" Grid.Row="2" Grid.Column="1" Text="{Binding alertId}" Visibility="Collapsed"></TextBlock>
                    </Grid>
                </DockPanel>
            </Border>
        </DataTemplate>
    </UserControl.Resources>
    <Grid>

    </Grid>
</UserControl>

The code behind I have

 public partial class NotificationView : UserControl
    {
        public int alertId { get; set; }

        public NotificationView()
        {
            InitializeComponent();
        }

        private void Border_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {

            var item = FindVisualChild.FindChild<TextBlock>(NFView, "tblAlertId"); //Problem is this line.
            alertId = Convert.ToInt32(item.Text);
            executeAlertClickCommand(ConsoleSettingsModel.GetInstance().SettingsCommandsData.AlertCommand, alertId);
        }

        internal void executeAlertClickCommand(WSMgrCommands cmd, int id) //Raising custom command
        {
            var wsParams = new WSAcknoledgedAlert();
            wsParams.alertId = id;
            if (cmd.CanExecute(wsParams))
            {
                cmd.Execute(wsParams);
            }
        }


    }

Answer 1

Where are you using this datatemplate in?? Is it in a listbox?? You should be able to access your control using the FrameworkTemplate.FindName method. First, get the ContentPresenter from one of the ListBoxItems:

ContentPresenter contentPresenter = FindVisualChild<ContentPresenter>(yourListBoxItemName);

Then get the DataTemplate from the ContentPresenter:

DataTemplate yourDataTemplate = contentPresenter.ContentTemplate;

Then get the MediaElement from the DataTemplate:

TextBlock yourTextBox = yourDataTemplate.FindName("tblAlertId", contentPresenter) 
as TextBlock;
if (yourTextBox != null)
{
    alertId = Convert.ToInt32(item.Text);
executeAlertClickCommand(ConsoleSettingsModel.GetInstance().SettingsCommandsData.AlertCommand, alertId);
}

Please see the FrameworkTemplate.FindName Method page on MSDN for more information. http://msdn.microsoft.com/en-us/library/system.windows.frameworktemplate.findname.aspx

Answer 2

try to find text block using LogiclTreeHelper class like,

private TextBlock GetTopParent()
    {
        DependencyObject dpParent = this.Parent;
        do
        {
            dpParent = LogicalTreeHelper.GetParent(dpParent);
        } while (dpParent.GetType().BaseType != typeof(UserControl));
        return dpParent as TextBlock;
    }

replace the line while (dpParent.GetType().BaseType != typeof(TextBlock));

Answer 3

For me, since I had added the controls at run time, I had to register them before using the findName method.

StackPanel sp = new StackPanel
{
   Name = "mySP",
   Orientation = Orientation.Horizontal,
};

//need to register the control so i can find it by name
RegisterName(sp.Name, sp);

//now I can find control by name 
StackPanel sp = (StackPanel)mainStackPanel.FindName("mySP");