判断IP地址

首先我们先设计好一个界面，如下图：

需要写一个设计器支持所需的代码方法：
public Frm_Main()
{
InitializeComponent();
}
namespace ValidateIP
{
partial class Frm_Main
{
///
/// 必需的设计器变量。
///
private System.ComponentModel.IContainer components = null;

    /// 

    /// 清理所有正在使用的资源。
    /// 
    /// 如果应释放托管资源，为 true；否则为 false。
    protected override void Dispose(bool disposing)
    {
        if (disposing && (components != null))
        {
            components.Dispose();
        }
        base.Dispose(disposing);
    }

    #region Windows 窗体设计器生成的代码

    /// 

    /// 设计器支持所需的方法 - 不要
    /// 使用代码编辑器修改此方法的内容。
    /// 
    private void InitializeComponent()
    {
        this.textBox1 = new System.Windows.Forms.TextBox();
        this.btn_Validate = new System.Windows.Forms.Button();
        this.label1 = new System.Windows.Forms.Label();
        this.groupBox1 = new System.Windows.Forms.GroupBox();
        this.groupBox2 = new System.Windows.Forms.GroupBox();
        this.groupBox1.SuspendLayout();
        this.groupBox2.SuspendLayout();
        this.SuspendLayout();
        // 
        // textBox1
        // 
        this.textBox1.Location = new System.Drawing.Point(112, 31);
        this.textBox1.Name = "textBox1";
        this.textBox1.Size = new System.Drawing.Size(171, 21);
        this.textBox1.TabIndex = 0;
        // 
        // btn_Validate
        // 
        this.btn_Validate.Location = new System.Drawing.Point(86, 20);
        this.btn_Validate.Name = "btn_Validate";
        this.btn_Validate.Size = new System.Drawing.Size(141, 23);
        this.btn_Validate.TabIndex = 1;
        this.btn_Validate.Text = "验证IP";
        this.btn_Validate.UseVisualStyleBackColor = true;
        this.btn_Validate.Click += new System.EventHandler(this.btn_Validate_Click);
        // 
        // label1
        // 
        this.label1.AutoSize = true;
        this.label1.Location = new System.Drawing.Point(23, 35);
        this.label1.Name = "label1";
        this.label1.Size = new System.Drawing.Size(89, 12);
        this.label1.TabIndex = 2;
        this.label1.Text = "请输入IP地址：";
        // 
        // groupBox1
        // 
        this.groupBox1.Controls.Add(this.label1);
        this.groupBox1.Controls.Add(this.textBox1);
        this.groupBox1.Location = new System.Drawing.Point(7, 6);
        this.groupBox1.Name = "groupBox1";
        this.groupBox1.Size = new System.Drawing.Size(315, 76);
        this.groupBox1.TabIndex = 3;
        this.groupBox1.TabStop = false;
        this.groupBox1.Text = "输入信息";
        // 
        // groupBox2
        // 
        this.groupBox2.Controls.Add(this.btn_Validate);
        this.groupBox2.Location = new System.Drawing.Point(7, 89);
        this.groupBox2.Name = "groupBox2";
        this.groupBox2.Size = new System.Drawing.Size(315, 54);
        this.groupBox2.TabIndex = 4;
        this.groupBox2.TabStop = false;
        this.groupBox2.Text = "操作";
        // 
        // Frm_Main
        // 
        this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
        this.ClientSize = new System.Drawing.Size(329, 146);
        this.Controls.Add(this.groupBox2);
        this.Controls.Add(this.groupBox1);
        this.Name = "Frm_Main";
        this.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen;
        this.Text = "使用正则表达式验证IP地址";
        this.groupBox1.ResumeLayout(false);
        this.groupBox1.PerformLayout();
        this.groupBox2.ResumeLayout(false);
        this.ResumeLayout(false);

    }

    #endregion

    private System.Windows.Forms.TextBox textBox1;
    private System.Windows.Forms.Button btn_Validate;
    private System.Windows.Forms.Label label1;
    private System.Windows.Forms.GroupBox groupBox1;
    private System.Windows.Forms.GroupBox groupBox2;
}

}
接下来双击“验证IP”button 会进入到它的点击事件

    private void btn_Validate_Click(object sender, EventArgs e)
    {
        if (IPCheck(textBox1.Text))//验证IP是否正确
        {
            MessageBox.Show("输入ＩＰ正确");//弹出消息对话框
        }
        else { MessageBox.Show("输入ＩＰ不正确"); }//弹出消息对话框
    }

    /// 

    /// 验证IP是否正确
    /// 
    /// IP地址字符串
    /// 方法返回布尔值
    public bool IPCheck(string IP)
    {
        string num = "(25[0-5]|2[0-4]\\d|[0-1]\\d{2}|[1-9]?\\d)";//创建正则表达式字符串
        return Regex.IsMatch(IP,//使用正则表达式判断是否匹配
            ("^" + num + "\\." + num + "\\." + num + "\\." + num + "$"));
    }

运行效果如下：