C#利用委托进行多线程访问控件

 public  partial  class  Form1 : Form
    {
        /*
         * 界面上有一个button,和一个textbox，点击button1时，开始一个新线程，新线程中有一个方法，从0开始计数
         * 并累加，且将每一个新的数字显示到textbox1中去
         * */
        public  Form1()
        {
            InitializeComponent();
        }

        public  delegate  void  SetTextDelegate( int  text);

        private  void  button1_Click( object  sender, EventArgs e)
        {
            Thread th =  new  Thread( new  ThreadStart(SetText));
            th.Start();
        }
        private  void  SetText()
        {
            for  ( int  a=0;a<1000000;a++)
            {
                if  (textBox1.InvokeRequired)
                {
                    textBox1.Invoke( new  SetTextDelegate(SetTextDo), a);
                }
            }
        }
        public  void  SetTextDo( int  i)
        {
            textBox1.Text = i.ToString();
        }
    }
 #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
        /// 使用代码编辑器修改此方法的内容。
        /// </summary>
        private  void  InitializeComponent()
        {
            this .button1 =  new  System.Windows.Forms.Button();
            this .textBox1 =  new  System.Windows.Forms.TextBox();
            this .SuspendLayout();
            //
            // button1
            //
            this .button1.Location =  new  System.Drawing.Point(13, 23);
            this .button1.Name =  "button1" ;
            this .button1.Size =  new  System.Drawing.Size(75, 23);
            this .button1.TabIndex = 0;
            this .button1.Text =  "button1" ;
            this .button1.UseVisualStyleBackColor =  true ;
            this .button1.Click +=  new  System.EventHandler( this .button1_Click);
            //
            // textBox1
            //
            this .textBox1.Location =  new  System.Drawing.Point(145, 23);
            this .textBox1.Name =  "textBox1" ;
            this .textBox1.Size =  new  System.Drawing.Size(100, 21);
            this .textBox1.TabIndex = 1;
            //
            // Form1
            //
            this .AutoScaleDimensions =  new  System.Drawing.SizeF(6F, 12F);
            this .AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this .ClientSize =  new  System.Drawing.Size(284, 262);
            this .Controls.Add( this .textBox1);
            this .Controls.Add( this .button1);
            this .Name =  "Form1" ;
            this .Text =  "Form1" ;
            this .ResumeLayout( false );
            this .PerformLayout();

        }