如何验证类属性中的必填字段？

Question

我想要一种简单的方法来确保类中的某些属性包含值和/或在一个范围内（即：长度不超过 50 个字符）。我使用了关于如何验证类属性的问题和答案？不幸的是，我无法让它工作。

为了测试它，我使用 C# 创建了一个非常简单的 WinForm 示例。即使我做的一切都一样，但当我应用不正确的值（即：将年龄设置为高于允许的限制）时，它永远不会引发验证异常。

有人可以解释为什么它不抛出异常吗？就好像这个类不知道它应该使用必需的属性。

表格1.cs

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.ComponentModel.DataAnnotations;

namespace RequiredFieldsInClassExample {
public partial class Form1 : Form {
    public Form1() {
        InitializeComponent();
    }

    private void btnTest_Click(object sender, EventArgs e) {
        try {
            lstStatus.Items.Clear();
            lstStatus.Items.Add("Creating list of people");
            List<Person> CollectionOfPeople = new List<Person>();

            lstStatus.Items.Add("Creating a good person");
            Person Jeff = new Person();
            Jeff.Age = 33;
            Jeff.Firstname = "Jeff";
            Jeff.Lastname = "Jefferson";
            Jeff.GroupCode = "JJJ";

            CollectionOfPeople.Add(Jeff);

            lstStatus.Items.Add("Creating a bad person");
            Person Tim = new Person();
            Tim.Age = 444;
            Tim.Firstname = "";
            Tim.Lastname = "";
            Tim.GroupCode = "";

            CollectionOfPeople.Add(Tim);

            lstStatus.Items.Add("Done");
        } catch (ValidationException Exp) {
            MessageBox.Show(this, Exp.Message, "Validation Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
        } catch (Exception Exp) {
            MessageBox.Show(this, Exp.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
        }
    }
}
}

人物.cs

using System.ComponentModel.DataAnnotations;

public class Person {
private int m_iAge = 1;
private string m_sFirstname = "Unknown";
private string m_sLastname = "";
private string m_sGroupCode = "AAA";

//[Required(ErrorMessage = "Age is a required field.")]
//[Range(1, 100, ErrorMessage = "A persons age must be between 1 and 100.")]
[Required, Range(1, 100)]
public int Age
{
    get { return m_iAge; }
    set { m_iAge = value; }
}

//[Required(ErrorMessage = "Firstname is a required field.")]
[Required]
public string Firstname
{
    get { return m_sFirstname; }
    set { m_sFirstname = value; }
}

public string Lastname
{
    get { return m_sLastname; }
    set { m_sLastname = value; }
}

//[StringLength(3)]
public string GroupCode
{
    get { return m_sGroupCode; }
    set { m_sGroupCode = value; }
}
}

Answer 1

在 Person 类中添加一个新方法来执行验证。新的“验证”方法适用于所需的值、范围和字符串长度。

人物.cs

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Text;

public class Person {
private int m_iAge = 1;
private string m_sFirstname = "Unknown";
private string m_sLastname = "";
private string m_sGroupCode = "AAA";

[Required(ErrorMessage = "Age is a required field.")]
[Range(1, 100, ErrorMessage = "A persons age must be between 1 and 100.")]
public int Age
{
    get { return m_iAge; }
    set { m_iAge = value; }
}

[Required(ErrorMessage = "Firstname is a required field.")]
public string Firstname
{
    get { return m_sFirstname; }
    set { m_sFirstname = value; }
}

public string Lastname
{
    get { return m_sLastname; }
    set { m_sLastname = value; }
}

[StringLength(3, MinimumLength = 3)]
public string GroupCode
{
    get { return m_sGroupCode; }
    set { m_sGroupCode = value; }
}

public void Validate() {
    ValidationContext context = new ValidationContext(this, serviceProvider: null, items: null);
    List<ValidationResult> results = new List<ValidationResult>();
    bool isValid = Validator.TryValidateObject(this, context, results, true);

    if (isValid == false) {
        StringBuilder sbrErrors = new StringBuilder();
        foreach (var validationResult in results) {
            sbrErrors.AppendLine(validationResult.ErrorMessage);
        }
        throw new ValidationException(sbrErrors.ToString());
    }
}
}

回到表单背后的代码，您只需要为每个类调用 Validate 方法。

表格1.cs

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.ComponentModel.DataAnnotations;

namespace RequiredFieldsInClassExample {
public partial class Form1 : Form {
    public Form1() {
        InitializeComponent();
    }

    private void btnTest_Click(object sender, EventArgs e) {
        try {
            lstStatus.Items.Clear();
            lstStatus.Items.Add("Creating list of people");
            List<Person> CollectionOfPeople = new List<Person>();

            lstStatus.Items.Add("Creating a good person");
            Person Jeff = new Person();
            Jeff.Age = 33;
            Jeff.Firstname = "Jeff";
            Jeff.Lastname = "Jefferson";
            Jeff.GroupCode = "JJJ";
            // LOOK! This line was added
            Jeff.Validate();

            CollectionOfPeople.Add(Jeff);

            lstStatus.Items.Add("Creating a bad person");
            Person Tim = new Person();
            Tim.Age = 444;
            Tim.Firstname = "";
            Tim.Lastname = "";
            Tim.GroupCode = "";
            // LOOK! This line was added
            Tim.Validate();

            CollectionOfPeople.Add(Tim);

            lstStatus.Items.Add("Done");
        } catch (ValidationException Exp) {
            MessageBox.Show(this, Exp.Message, "Validation Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
        } catch (Exception Exp) {
            MessageBox.Show(this, Exp.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
        }
    }
}
}