WPF how do I create a textbox dynamically and find the textbox on a button click?

If you want to do a comprehensive search through the visual tree of controls, you can use the VisualTreeHelper class.

Use the following code to iterate through all of the visual children of a control:

for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parentObj); i++)
{
    DependencyObject child = VisualTreeHelper.GetChild(parent, i);

    if (child is TextBox)
        // Do something
}

If you want to search down into the tree, you will want to perform this loop recursively, like so:

public delegate void TextBoxOperation(TextBox box);

public bool SearchChildren(DependencyObject parent, TextBoxOperation op)
{
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)
    {
        DependencyObject child = VisualTreeHelper.GetChild(parent, i);

        TextBox box = child as TextBox;

        if (box != null)
        {
            op.Invoke(box);
            return true;
        }

        bool found = SearchChildren(child, op);

        if (found)
            return true;
    }
}

You can get your original click handler to work by registering the name of the text box:

someStackPanel.RegisterName(txtNumber.Name, txtNumber);

This will then allow you to call FindName on the StackPanel and find the TextBox.


Josh G had the clue that fixed this code: use RegisterName().

Three benefits here:

  1. Doesn't use a member variable to save the reference to the dynamically created TextBox.
  2. Compiles.
  3. Complete code.

    using System;
    using System.Windows;
    using System.Windows.Controls;
    
    namespace AddControlsDynamically
    {
        public partial class Window1 : Window
        {
            public void Window_Loaded(object sender, RoutedEventArgs e)
            {
                GenerateControls();
            }
            public void GenerateControls()
            {
                Button btnClickMe = new Button();
                btnClickMe.Content = "Click Me";
                btnClickMe.Name = "btnClickMe";
                btnClickMe.Click += new RoutedEventHandler(this.CallMeClick);
                someStackPanel.Children.Add(btnClickMe);
                TextBox txtNumber = new TextBox();
                txtNumber.Name = "txtNumber";
                txtNumber.Text = "1776";
                someStackPanel.Children.Add(txtNumber);
                someStackPanel.RegisterName(txtNumber.Name, txtNumber);
            }
            protected void CallMeClick(object sender, RoutedEventArgs e)
            {
                TextBox txtNumber = (TextBox) this.someStackPanel.FindName("txtNumber");
                string message = string.Format("The number is {0}", txtNumber.Text);
                MessageBox.Show(message);
            }
        }
    }
    

Another method is to set the associated TextBox as Button Tag when instanciating them.

btnClickMe.Tag = txtNumber;

This way you can retrieve it back in event handler.

protected void ClickMeClick(object sender, RoutedEventArgs e)
{
    Button btnClickMe = sender as Button;
    if (btnClickMe != null)
    {
        TextBox txtNumber = btnClickMe.Tag as TextBox;
        // ...
    }
}