How to create databinding in code behind for a textblock that is created also in code behind?

Question

I have the following code :

private void Ok_Click(object sender, MouseButtonEventArgs e)
{
    MainWindow win = (MainWindow)Application.Current.MainWindow;
    int i = 1;  // counter for the name of each new textblock
    string name = String.Concat("sample", i);

    // add textblok to the document list of new samples

    if (File_name.Text != "")
    {
        TextBlock sampleText = new TextBlock();


        sampleText.Text = File_name.Text;
        sampleText.FontSize = 14;
        sampleText.FontFamily = new FontFamily("Sans-serif");
        sampleText.FontWeight = FontWeights.DemiBold;
        sampleText.Margin = new Thickness(20,0,0,0);
        sampleText.Name = name;
        sampleText.PreviewMouseDown += new MouseButtonEventHandler(test1);
        sampleText.Visibility = System.Windows.Visibility.Collapsed;

        //binding 

        Binding myBinding = new Binding();
        myBinding.Source = Application.Current;
        myBinding.Path = new PropertyPath("sampleName");
        myBinding.Mode = BindingMode.TwoWay;
        myBinding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
        sampleText.SetBinding(, myBinding);


        Grid.SetColumn(sampleText, 0);

        win.sp_s.Children.Add(sampleText);

        // checking if the drop down of sample is already open,
        //if so it will show the last textblock with pressing the arrow button.
        var TextBlock = win.sp_s.Children.OfType<TextBlock>().FirstOrDefault();
        if (TextBlock.Visibility == System.Windows.Visibility.Visible)
        {
            sampleText.Visibility = System.Windows.Visibility.Visible;
        }
    }
    i += 1;  // increasing the loop of names by 1
    this.Close();
}

I want to set the target property of the SetBinding method to TextBlock.TextProperty but whenever I write TextBlock I get an error stating

Cannot use local variable 'TextBlock' before it is declared.

Answer 1

I suspect the issue is with this code -

var TextBlock = win.sp_s.Children.OfType<TextBlock>().FirstOrDefault();
        if (TextBlock.Visibility == System.Windows.Visibility.Visible)
        {
            sampleText.Visibility = System.Windows.Visibility.Visible;
        }

You have declared a variable name as "TextBlock". The TextBlock.Text property you are trying to set inside the binding is getting confused with this variable name you have declared below it. If you rename this variable the issue might get fixed.

 var textblock = win.sp_s.Children.OfType<TextBlock>().FirstOrDefault();
 if (textblock.Visibility == System.Windows.Visibility.Visible)
     {
         sampleText.Visibility = System.Windows.Visibility.Visible;
     }