TextBox

Auto completion from a collection of strings

var source = new AutoCompleteStringCollection();

// Add your collection of strings.
source.AddRange(new[] { "Guybrush Threepwood", "LeChuck" });

var textBox = new TextBox
{
    AutoCompleteCustomSource = source,
    AutoCompleteMode = AutoCompleteMode.SuggestAppend,
    AutoCompleteSource = AutoCompleteSource.CustomSource
};

form.Controls.Add(textBox);

This will autocomplete the as the user tries to type G or L.

AutoCompleteMode.SuggestAppend will both display a list of suggested values and it will auto type the first match, Append only and Suggest only are available, too.

Allow only digits in the text

textBox.KeyPress += (sender, e) => e.Handled = !char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar);

This will only permit the use of digits and control characters in the TextBox, other combinations are possible using the same approach of setting the Handle property to true to block the text.

The user can still copy/paste unwanted characters so an additional check should be on the TextChanged to cleanse the input:

textBox.TextChanged += (sender, e) => textBox.Text = Regex.Match(textBox.Text, @"\d+").Value

In this example a Regular expression is used to filter the text.

NumericUpDown should be preferred for numbers when possible.

How to scroll to the end

textBox.SelectionStart = textBox.TextLength;
textBox.ScrollToCaret();

Applying the same principle, SelectionStart can be set to 0 to scroll to the top or to a specific number to go to a specific character.

Adding a Placeholder to textbox

This code places the hint text at form load and manipulates it as follows:

private void Form_load(object sender, EventArgs e)
{
    textBox.Text = "Place Holder text...";
}

private void textBox_Enter(object sender, EventArgs e)
{
    if(textBox.Text == "Place Holder text...")
    {
        textBox.Text = "";
    }
}

private void textBox_Leave(object sender, EventArgs e)
{
    if(textBox.Text.Trim() == "")
    {
        textBox.Text = "Place Holder text...";
    }
}

VB.NET

Private Sub Form_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    textBox.Text = "Place Holder text..."
End Sub

Private Sub textBox_GotFocus(sender as Object,e as EventArgs) Handles textBox.GotFocus
    if Trim(textBox.Text) = "Place Holder text..." Then
        textBox.Text = ""
    End If
End Sub

Private Sub textBox_LostFocus(sender as Object,e as EventArgs) Handles textBox.LostFocus
    if Trim(textBox.Text) = "" Then
        textBox.Text = "Place Holder text..."
    End If
End Sub