From介绍

窗体页面命名一般以Frm开头, 例如: FrmUser
窗体页面添加后一般分为:
FrmUser.cs[设计] 窗体设计类(看到的是窗体设计),如果点击查看源代码将定位到FrmUser.cs部分类
FrmUser.Designer.cs 窗体布局代码,自动生成对应的控件代码
FrmUser.resx 窗体的资源

进入FrmUser.cs部分类:

public partial class FrmUser : Form
{
    public FrmUser()
    {
        InitializeComponent();
    } 
}

所有窗体页面类继承Form类,并且有一个无参构造函数, 点击进入InitializeComponent(), 显示的是Form页面的所有控件信息,也是窗体类的部分类

partial class FrmUser
{
    /// <summary>
    /// 必需的设计器变量。
    /// </summary>
    private System.ComponentModel.IContainer components = null;

    /// <summary>
    /// 清理所有正在使用的资源。
    /// </summary>
    /// <param name="disposing">如果应释放托管资源，为 true；否则为 false。</param>
    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

    /// <summary>
    /// 设计器支持所需的方法 - 不要修改
    /// 使用代码编辑器修改此方法的内容。
    /// </summary>
    private void InitializeComponent()
    {
        System.ComponentModel.ComponentResourceManager resources = new System.ComponentModel.ComponentResourceManager(typeof(FrmUser));
        this.label1 = new System.Windows.Forms.Label();
        this.textBox1 = new System.Windows.Forms.TextBox();
        this.button1 = new System.Windows.Forms.Button();
        this.button2 = new System.Windows.Forms.Button();
        this.SuspendLayout();
        // 
        // label1
        // 
        resources.ApplyResources(this.label1, "label1");
        this.label1.Name = "label1";
        // 
        // textBox1
        // 
        resources.ApplyResources(this.textBox1, "textBox1");
        this.textBox1.Name = "textBox1";
        // 
        // button1
        // 
        this.button1.DialogResult = System.Windows.Forms.DialogResult.Cancel;
        resources.ApplyResources(this.button1, "button1");
        this.button1.Name = "button1";
        this.button1.UseVisualStyleBackColor = true;
        this.button1.Click += new System.EventHandler(this.button1_Click);
        // 
        // button2
        // 
        this.button2.DialogResult = System.Windows.Forms.DialogResult.Cancel;
        resources.ApplyResources(this.button2, "button2");
        this.button2.Name = "button2";
        this.button2.UseVisualStyleBackColor = true;
        this.button2.Click += new System.EventHandler(this.button2_Click);
        // 
        // FrmUser
        // 
        resources.ApplyResources(this, "$this");
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
        this.BackColor = System.Drawing.SystemColors.ButtonShadow;
        this.CancelButton = this.button2;
        this.Controls.Add(this.button2);
        this.Controls.Add(this.button1);
        this.Controls.Add(this.textBox1);
        this.Controls.Add(this.label1);
        this.Name = "FrmUser";
        this.ResumeLayout(false);
        this.PerformLayout();

    }

    #endregion

    private System.Windows.Forms.Label label1;
    private System.Windows.Forms.TextBox textBox1;
    private System.Windows.Forms.Button button1;
    private System.Windows.Forms.Button button2;
}