您可以使用TextChanged事件

private void textBox_BiggerThan_TextChanged(object sender, EventArgs e)
{
    long a;
    if (! long.TryParse(textBox_BiggerThan.Text, out a))
    {
        // If not int clear textbox text or Undo() last operation
        textBox_LessThan.Clear();
    }
}

很抱歉吵醒死人，但我想有人可能会觉得这对将来的参考有用。

以下是我的处理方法。它处理浮点数，但可以很容易地修改为整数。

基本上你只能按0 - 9和。

前面只能有一个0。

所有其他字符将被忽略，光标位置保持不变。

    private bool _myTextBoxChanging = false;

    private void myTextBox_TextChanged(object sender, EventArgs e)
    {
        validateText(myTextBox);
    }

    private void validateText(TextBox box)
    {
        // stop multiple changes;
        if (_myTextBoxChanging)
            return;
        _myTextBoxChanging = true;

        string text = box.Text;
        if (text == "")
            return;
        string validText = "";
        bool hasPeriod = false;
        int pos = box.SelectionStart;
        for (int i = 0; i < text.Length; i++ )
        {
            bool badChar = false;
            char s = text[i];
            if (s == '.')
            {
                if (hasPeriod)
                    badChar = true;
                else
                    hasPeriod = true;
            }
            else if (s < '0' || s > '9')
                badChar = true;

            if (!badChar)
                validText += s;
            else
            {
                if (i <= pos)
                    pos--;
            }
        }

        // trim starting 00s
        while (validText.Length >= 2 && validText[0] == '0')
        {
            if (validText[1] != '.')
            {
                validText = validText.Substring(1);
                if (pos < 2)
                    pos--;
            }
            else
                break;
        }

        if (pos > validText.Length)
            pos = validText.Length;
        box.Text = validText;
        box.SelectionStart = pos;
        _myTextBoxChanging = false;
    }

下面是一个快速修改的int版本:

    private void validateText(TextBox box)
    {
        // stop multiple changes;
        if (_myTextBoxChanging)
            return;
        _myTextBoxChanging = true;

        string text = box.Text;
        if (text == "")
            return;
        string validText = "";
        int pos = box.SelectionStart;
        for (int i = 0; i < text.Length; i++ )
        {
            char s = text[i];
            if (s < '0' || s > '9')
            {
                if (i <= pos)
                    pos--;
            }
            else
                validText += s;
        }

        // trim starting 00s 
        while (validText.Length >= 2 && validText.StartsWith("00")) 
        { 
            validText = validText.Substring(1); 
            if (pos < 2) 
                pos--; 
        } 

        if (pos > validText.Length)
            pos = validText.Length;
        box.Text = validText;
        box.SelectionStart = pos;
        _myTextBoxChanging = false;
    }

我一直致力于一个组件的集合来完成WinForms中缺失的东西，这里是:高级表单

特别地，这是一个正则文本框类

/// <summary>Represents a Windows text box control that only allows input that matches a regular expression.</summary>
public class RegexTextBox : TextBox
{
    [NonSerialized]
    string lastText;

    /// <summary>A regular expression governing the input allowed in this text field.</summary>
    [Browsable(false), EditorBrowsable(EditorBrowsableState.Never)]
    [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
    public virtual Regex Regex { get; set; }

    /// <summary>A regular expression governing the input allowed in this text field.</summary>
    [DefaultValue(null)]
    [Category("Behavior")]
    [Description("Sets the regular expression governing the input allowed for this control.")]
    public virtual string RegexString {
        get {
            return Regex == null ? string.Empty : Regex.ToString();
        }
        set {
            if (string.IsNullOrEmpty(value))
                Regex = null;
            else
                Regex = new Regex(value);
        }
    }

    protected override void OnTextChanged(EventArgs e) {
        if (Regex != null && !Regex.IsMatch(Text)) {
            int pos = SelectionStart - Text.Length + (lastText ?? string.Empty).Length;
            Text = lastText;
            SelectionStart = Math.Max(0, pos);
        }

        lastText = Text;

        base.OnTextChanged(e);
    }
}

简单地添加像myNumbericTextBox这样的东西。RegexString = "^(\\d+|)$";应该足够了。

我会在KeyDown事件中处理它。

void TextBox_KeyDown(object sender, KeyEventArgs e)
        {
            char c = Convert.ToChar(e.PlatformKeyCode);
            if (!char.IsDigit(c))
            {
                e.Handled = true;
            }
        }

整数和浮点数都需要被接受，包括负数。

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    // Text
    string text = ((Control) sender).Text;

    // Is Negative Number?
    if (e.KeyChar == '-' && text.Length == 0)
    {
        e.Handled = false;
        return;
    }

    // Is Float Number?
    if (e.KeyChar == '.' && text.Length > 0 && !text.Contains("."))
    {
        e.Handled = false;
        return;
    }

    // Is Digit?
    e.Handled = (!char.IsDigit(e.KeyChar) && !char.IsControl(e.KeyChar));
}

最简单粗暴的方法是使用组合框而不是带有只读的文本框。当然，只有当你希望用户使用一个合理的整数集，而不是试图接近无穷大时，它才有用。