How to paste text in textbox current cursor?

Question

How do you paste text into a TextBox at the current cursor position in Windows Forms?

Not textbox1 += string

Answer 1

I realize this is an old post but i hope this collection of methods for TextBox will help others struggling with manipulating this control.

public static class InputExtensions
{
    public static void InsertText(this TextBox textbox, string strippedText)
    {
        int start = textbox.SelectionStart;
        string newTxt = textbox.Text;
        newTxt = newTxt.Remove(textbox.SelectionStart, textbox.SelectionLength);
        newTxt = newTxt.Insert(textbox.SelectionStart, strippedText);
        textbox.Text = newTxt;
        textbox.SelectionStart = start + strippedText.Length;
    }

    public static void Delete(this TextBox textbox)
    {
        var startLength = textbox.Text.Length;
        if (textbox.Text.Length == 0) return;
        var isSelection = textbox.SelectionLength > 0;
        var length = Math.Max(!isSelection ? 1 : textbox.SelectionLength, 0);
        int start = textbox.SelectionStart;
        string newTxt = textbox.Text;
        if (length == 0 || start + length > startLength) return;
        newTxt = newTxt.Remove(start, length);
        textbox.Text = newTxt;
        textbox.SelectionStart = start;
    }

    public static void Backspace(this TextBox textbox)
    {
        var startLength = textbox.Text.Length;
        if (startLength == 0) return;
        var isSelection = textbox.SelectionLength > 0;
        var length = Math.Max(!isSelection ? 1 : textbox.SelectionLength, 0);
        int start = Math.Max(textbox.SelectionStart - 1, 0);
        if (length == 0 || start == 0) return;
        string newTxt = textbox.Text;
        newTxt = newTxt.Remove(start, length);
        textbox.Text = newTxt;
        textbox.SelectionStart = start;
    }

    public static void MoveCaretRight(this TextBox textbox)
    {
        textbox.SelectionStart = Math.Min(Math.Max(0, textbox.SelectionStart + 1), textbox.Text.Length);
    }

    public static void MoveCaretLeft(this TextBox textbox)
    {
        textbox.SelectionStart = Math.Min(Math.Max(0, textbox.SelectionStart - 1), textbox.Text.Length);
    }

    public static bool IsModifier(this KeyEventArgs e)
    {
        return e.Control || e.Alt || e.Shift;
    }

    public static bool IsNavigationKey(this KeyEventArgs e)
    {
        switch (e.KeyCode)
        {
            case Keys.Up:
            case Keys.Down:
            case Keys.Left:
            case Keys.Right:
            case Keys.PageUp:
            case Keys.PageDown:
                return true;
        }
        return false;
    }

    public static bool IsNonNumber(this KeyEventArgs e)
    {
        var key = (char)e.KeyCode;
        return
            char.IsLetter(key) ||
            char.IsSymbol(key) ||
            char.IsWhiteSpace(key) ||
            char.IsPunctuation(key);
    }

    public static void Paste(TextBox textbox, Func charFilter = null)
    {
        var pasteText = Clipboard.GetText();
        var strippedText = "";
        for (var i = 0; i < pasteText.Length; i++)
        {
            if (charFilter == null || charFilter(pasteText[i], i))
                strippedText += pasteText[i].ToString();
        }
        InsertText(textbox, strippedText);
    }
}