【WinForm窗体控件开发】之二 简单的窗体控件

我们做一个简单的例子：

下面是继承自Control类的自定义窗体控件的代码：

using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;

namespace 之二简单的窗体控件Demo
{
    public class FirstControl:Control
    {
        /// <summary>
        /// Constructor
        /// </summary>
        public FirstControl() { }

        #region FirstControl 使用该属性来设置从 Control 继承的 Text 属性的显示格式
        // ContentAlignment is an enumeration defined in the System.Drawing
        // namespace that specifies the alignment of content on a drawing 
        // surface.
        private ContentAlignment alignmentValue = ContentAlignment.MiddleLeft;
        
        [
        Category("Alignment"),
        Description("Specifies the alignment of text.")
        ]
        public ContentAlignment TextAlignment
        {
            get
            {
                return alignmentValue;
            }
            set
            {
                alignmentValue = value;

                // The Invalidate method invokes the OnPaint method described 
                // in step 3.

                // 在设置更改控件可视显示的属性时，必须调用 Invalidate 方法来重新绘制该控件。
                // Invalidate 是在 Control 基类中定义的。
                Invalidate();
            }
        }
        #endregion


        /// <summary>
        /// 重写从 Control 继承的受保护的 OnPaint 方法，以便为控件提供呈现逻辑。
        /// 如果不改写 OnPaint，您的控件将无法自行绘制。
        /// 在下面的代码片段中，OnPaint 方法显示从 Control 继承的 Text 属性，并使用 alignmentValue 字段指定的对齐方式。
        /// </summary>
        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
            
            StringFormat style = new StringFormat();
            style.Alignment = StringAlignment.Near;
            
            switch (alignmentValue)
            {
                case ContentAlignment.MiddleLeft:
                    style.Alignment = StringAlignment.Near;
                    break;
                case ContentAlignment.MiddleRight:
                    style.Alignment = StringAlignment.Far;
                    break;
                case ContentAlignment.MiddleCenter:
                    style.Alignment = StringAlignment.Center;
                    break;
            }

            // Call the DrawString method of the System.Drawing class to write text. 
            // Text and ClientRectangle are properties inherited from Control.
            e.Graphics.DrawString(
                Text,
                Font,
                new SolidBrush(ForeColor),
                ClientRectangle, style);

        } 
    }
}

namespace 之二简单的窗体控件Demo
{
    partial class Form1
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.firstControl1 = new 之二简单的窗体控件Demo.FirstControl();
            this.firstControl2 = new 之二简单的窗体控件Demo.FirstControl();
            this.firstControl3 = new 之二简单的窗体控件Demo.FirstControl();
            this.SuspendLayout();
            // 
            // firstControl1
            // 
            this.firstControl1.Location = new System.Drawing.Point(12, 24);
            this.firstControl1.Name = "firstControl1";
            this.firstControl1.Size = new System.Drawing.Size(122, 21);
            this.firstControl1.TabIndex = 0;
            this.firstControl1.Text = "firstControl1";
            this.firstControl1.TextAlignment = System.Drawing.ContentAlignment.MiddleLeft;
            // 
            // firstControl2
            // 
            this.firstControl2.Location = new System.Drawing.Point(12, 51);
            this.firstControl2.Name = "firstControl2";
            this.firstControl2.Size = new System.Drawing.Size(122, 23);
            this.firstControl2.TabIndex = 1;
            this.firstControl2.Text = "firstControl2";
            this.firstControl2.TextAlignment = System.Drawing.ContentAlignment.MiddleCenter;
            // 
            // firstControl3
            // 
            this.firstControl3.Location = new System.Drawing.Point(12, 80);
            this.firstControl3.Name = "firstControl3";
            this.firstControl3.Size = new System.Drawing.Size(122, 23);
            this.firstControl3.TabIndex = 2;
            this.firstControl3.Text = "firstControl3";
            this.firstControl3.TextAlignment = System.Drawing.ContentAlignment.MiddleRight;
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(214, 182);
            this.Controls.Add(this.firstControl3);
            this.Controls.Add(this.firstControl2);
            this.Controls.Add(this.firstControl1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.Load += new System.EventHandler(this.Form1_Load);
            this.ResumeLayout(false);

        }

        #endregion

        private FirstControl firstControl1;
        private FirstControl firstControl2;
        private FirstControl firstControl3;
    }
}

效果图：

控件编译后会在Toolbox工具箱中出现一个齿轮样子的小工具，直接在Form窗体上使用即可；

注意属性栏中最下面一个TextAligment属性，这是我们自己为FirstControl控件添加的属性

关于控件的常用的Attribute的详细介绍我们在下一节中进行详细介绍。