考虑使用FluentValidation之类的验证库。
首先创建一个具有要验证的属性的类，例如

public class Person
{
    public string UserName { get; set; }
    public string EmailAddress { get; set; }
    public string Password { get; set; }
    public string PasswordConfirmation { get; set; }
}

创建一个validator。

public class PersonValidator : AbstractValidator<Person>
{
    public PersonValidator()
    {
        RuleFor(person => person.UserName)
            .NotEmpty()
            .MinimumLength(3);

        RuleFor(person => person.EmailAddress).EmailAddress();
        RuleFor(person => person.Password.Length).GreaterThan( 7);
        RuleFor(person => person.Password).Equal(p => p.PasswordConfirmation);

    }
}

创建类的新示例，在本例中为Person。从控件填充值，然后通过Validate执行验证。
下面是一个模型，它使用StringBuilder创建一个可以呈现给用户的字符串。

Person person = new Person()
{
    UserName = "billyBob",
    Password = "my@Password1", 
    EmailAddress = "billyBob@gmailcom", 
    PasswordConfirmation = "my@Password1"
};

PersonValidator validator = new PersonValidator();
ValidationResult result = validator.Validate(person);
if (result.IsValid)
{
    // person is valid
}
else
{
    StringBuilder builder = new StringBuilder();
    foreach (var error in result.Errors)
    {
        builder.AppendLine(error.ErrorMessage);
    }
}

如果需要检查个别错误，如PropertyName（要验证的属性的名称）和ComparisonValue（属性不应等于的值），请深入研究ValidationResult。

注意电子邮件地址验证程序只检查电子邮件地址是否有@，因此如果您需要更多的自定义工作。

创建静态Extension Method是**“创建全局类（所以我只需要写一次......）"**的一种方法。

首先询问“确定有效表单需要哪些信息？”在interface中定义这些要求：

interface IValidate
{
    // Inputs needed
    public string Username { get; }
    public string Email { get; }
    public string Password { get; }
    public string Confirm { get; }
}

现在为实现IValidate的“any”表单声明一个扩展方法（这是您所询问的全局类）。

static class Extensions
{
    public static int ValidateForm(this IValidate @this, CancelEventArgs e)
    {
        if (@this.Username.Length < 3) return 1;
        if (!@this.Email.Contains("@")) return 2;
        if (@this.Password.Length < 7) return 3;
        if (!@this.Password.Equals(@this.Confirm)) return 4;
        return 0;
    }
}

Form类将能够使用this调用扩展。

var e = new new CancelEventArgs();
int error_number = this.ValidateForm(e);

表单验证示例

对于3个表单中的每一个，实现接口，这意味着3个表单类承诺或约定提供接口所需的信息（在本例中，通过从文本框中检索文本）。

public partial class MainForm : Form, IValidate
{
    #region I M P L E M E N T    I N T E R F A C E
    public string Username => textBoxUsername.Text;
    public string Email => textBoxEmail.Text;
    public string Password => textBoxPassword.Text;
    public string Confirm => textBoxConfirm.Text;
    #endregion I M P L E M E N T    I N T E R F A C E
    .
    .
    .
}

然后在任何文本框失去焦点或接收到Enter键时调用扩展方法。

public partial class MainForm : Form, IValidate
{        
    public MainForm()
    {
        InitializeComponent();
        foreach (Control control in Controls)
        {
            if(control is TextBox textBox)
            {
                textBox.TabStop = false;
                textBox.KeyDown += onAnyTextboxKeyDown;
                textBox.Validating += onAnyTextBoxValidating;
                textBox.TextChanged += (sender, e) =>
                {
                    if (sender is TextBox textbox) textbox.Modified = true;
                };
            }
        }
    }
    private void onAnyTextBoxValidating(object? sender, CancelEventArgs e)
    {
        if (sender is TextBox textBox)
        {
            // Call the extension method to validate.
            ErrorInt @int = (ErrorInt)this.ValidateForm(e);
            if (@int.Equals(ErrorInt.None))
            {
                labelError.Visible = false;
                buttonLogin.Enabled = true;
                return;
            }
            else if (textBox.Modified)
            {
                buttonLogin.Enabled = false;
                BeginInvoke(() =>
                {
                    switch (@int)
                    {
                        case ErrorInt.Username: textBoxUsername.Focus(); break;
                        case ErrorInt.Email: textBoxEmail.Focus(); break;
                        case ErrorInt.Password: textBoxPassword.Focus(); break;
                        case ErrorInt.Confirm: textBoxConfirm.Focus(); break;
                    }
                    labelError.Visible = true;
                    labelError.Text = typeof(ErrorInt)
                        .GetMember(@int.ToString())
                        .First()?
                        .GetCustomAttribute<DescriptionAttribute>()
                        .Description;
                    textBox.Modified = false;
                    textBox.SelectAll();
                });
            }
        }
    }
    private void onAnyTextboxKeyDown(object? sender, KeyEventArgs e)
    {
        if (sender is TextBox textbox)
        {
            if (e.KeyData.Equals(Keys.Return))
            {
                // Handle the Enter key.
                e.SuppressKeyPress = e.Handled = true;

                MethodInfo? validate = typeof(TextBox).GetMethod("OnValidating", BindingFlags.Instance | BindingFlags.NonPublic);
                CancelEventArgs eCancel = new CancelEventArgs();
                validate?.Invoke(textbox, new[] { eCancel });
            }
        }
    }
    .
    .
    .
}

其中：

enum ErrorInt
{
    None = 0,
    [Description("Username must be at least 3 characters.")]
    Username = 1,
    [Description("Valid email is required.")]
    Email = 2,
    [Description("Password must be at least 7 characters.")]
    Password = 3,
    [Description("Passwords must match.")]
    Confirm = 4,
}