C#中的全局变量

 

一、C#中的全局变量

C#中没有了像VB.Net中的全局变量，那么我们如何实现在不同的页面间传递参数呢？
下面举例说明如何实现这一功能.
1.新建一个项目.
2.在该工程中添加一个窗体Form1.
3.在该窗体中定义静态型字符串变量myTestStr1:
public static string myTestStr1="";
4.在该窗体的构造函数中对该变量进行赋值,并为该窗体类添加属性GetStrValue.

public Form_Form1()
         {
              InitializeComponent();
             
              myTestStr1="Hello!";
         }
         public string GetStrValue
         {
              get
              {
                   return myTestStr1;
              }
              set
              {
                   myTestStr1=value;
              }
         }      
5.在该工程中另添加一个窗体Form2.
6.在Form1窗体上添加一个button按钮(name:but_Test);
7.在Form1窗体的but_Test_Click 事件中添加以下代码:
private void but_Test_Click(object sender, System.EventArgs e)
         {
              Form2 frm1=new Form2();
              frm1.ShowDialog(this) ;
              frm1.Close();

         }
8.在Form2窗体上添加一个button按钮(name:but_Yes);
9.在Form1窗体的but_Yes_Click 事件中添加以下代码:
private void but_Yes_Click(object sender, System.EventArgs e)
         {
              MessageBox.Show (Form_Form1.myTestStr1 );    //直接访问. 显示.结果:" Hello!"
              Form_Form1 frm2=new Form_Form1();
              frm2.GetStrValue ="How do you do?";                                       //生成一个新的实例对该静态变量进行操作(修改该静态变量的值).
              MessageBox.Show (frm2.GetStrValue );                     //通过该实例的内部成员对它进行访问 .显示.结果: How do you do?"

              MessageBox.Show (Form_Form1.myTestStr1 );   //直接访问. 显示.结果:" How do you do?"

         }

二、在Windows窗体开发中使用Cache
Cache在程序设计时可以带来很大的便利，这点想必在web程序开发中大家都有深刻的体会！同样，在windows程序设计中也可以使用它。

使用时需要将web引用添加到窗体项目的引用中，下面以一个实例介绍之！
首先要将程序的Main（）函数放在一个添加的类里，这里就是AppMain类。下面是AppMain类的代码：

using System;
using System.Threading;
using System.Web;//添加引用
using System.Web.Caching; //添加引用

using System.Windows.Forms;

namespace WindowsApplication1
{
     public class AppMain
     {
          private static HttpRuntime _httpRuntime;

         public static Cache Cache
         {
              get
              {
                   EnsureHttpRuntime();
                   return HttpRuntime.Cache;
              }
         }

          [STAThread]
         static void Main()
         {
              Application.Run(new Form1());
         }
     
          private static void EnsureHttpRuntime()
         {
              if( null == _httpRuntime )
              {
                   try
                   {
                        Monitor.Enter( typeof( AppMain ) );
                        if( null == _httpRuntime )
                       {
                            // Create an Http Content to give us access to the cache.
                            _httpRuntime = new HttpRuntime();
                       }
                   }
                   finally
                   {
                        Monitor.Exit( typeof( AppMain ) );
                   }
              }
         }
     }
}
然后在Form1窗体中定义和使用Cache，代码如下：
using System;
using System.Web;//添加引用
using System.Web.Caching; //添加引用
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

namespace WindowsApplication1
{
     ///

     /// Form1 的摘要说明。
     ///

     public class Form1 : System.Windows.Forms.Form
     {
          private System.Windows.Forms.Label label1;
          private System.Windows.Forms.Label label2;
          private System.Windows.Forms.TextBox txtValueToPutInCache;
          private System.Windows.Forms.TextBox txtValueInCache;
          private System.Windows.Forms.Button btnPutInCache;
          private System.Windows.Forms.Button btnGetFromButton;
     
          private const string CACHE_KEY = "APPCACHEKEY";
     
         ///

         /// Required designer variable.
         ///

          private System.ComponentModel.Container components = null;
     
         public Form1()
         {
              //
              // Required for Windows Form Designer support
              //
              InitializeComponent();
        
              //
              // TODO: Add any constructor code after InitializeComponent call
              //
         }
     
         ///

         /// Clean up any resources being used.
         ///

          protected override void Dispose( bool disposing )
         {
              if( disposing )
              {
                   if (components != null)
                   {
                        components.Dispose();
                   }
              }
              base.Dispose( disposing );
         }

          #region Windows Form Designer generated code
         ///

         /// Required method for Designer support - do not modify
         /// the contents of this method with the code editor.
         ///

          private void InitializeComponent()
         {
              this.label1 = new System.Windows.Forms.Label();
              this.label2 = new System.Windows.Forms.Label();
              this.txtValueToPutInCache = new System.Windows.Forms.TextBox();
              this.txtValueInCache = new System.Windows.Forms.TextBox();
              this.btnPutInCache = new System.Windows.Forms.Button();
              this.btnGetFromButton = new System.Windows.Forms.Button();
              this.SuspendLayout();
              //
              // label1
              //
              this.label1.AutoSize = true;
              this.label1.Location = new System.Drawing.Point(8, 16);
              this.label1.Name = "label1";
              this.label1.Size = new System.Drawing.Size(113, 16);
              this.label1.TabIndex = 0;
              this.label1.Text = "Value to put in cache:";
              //
              // label2
              //
              this.label2.AutoSize = true;
              this.label2.Location = new System.Drawing.Point(8, 40);
              this.label2.Name = "label2";
              this.label2.Size = new System.Drawing.Size(95, 16);
              this.label2.TabIndex = 1;
              this.label2.Text = "Value from cache:";
              //
              // txtValueToPutInCache
              //
              this.txtValueToPutInCache.Location = new System.Drawing.Point(128, 16);
              this.txtValueToPutInCache.Name = "txtValueToPutInCache";
              this.txtValueToPutInCache.Size = new System.Drawing.Size(200, 20);
              this.txtValueToPutInCache.TabIndex = 2;
              this.txtValueToPutInCache.Text = "";
              //
              // txtValueInCache
              //
              this.txtValueInCache.Location = new System.Drawing.Point(128, 40);
              this.txtValueInCache.Name = "txtValueInCache";
              this.txtValueInCache.ReadOnly = true;
              this.txtValueInCache.Size = new System.Drawing.Size(200, 20);
              this.txtValueInCache.TabIndex = 3;
              this.txtValueInCache.Text = "";
              //
              // btnPutInCache
              //
              this.btnPutInCache.Location = new System.Drawing.Point(352, 16);
              this.btnPutInCache.Name = "btnPutInCache";
               this.btnPutInCache.Size = new System.Drawing.Size(104, 23);
              this.btnPutInCache.TabIndex = 4;
              this.btnPutInCache.Text = "Put in Cache";
              this.btnPutInCache.Click +=
                   new System.EventHandler(this.btnPutInCache_Click);
              //
              // btnGetFromButton
              //
              this.btnGetFromButton.Location = new System.Drawing.Point(352, 40);
              this.btnGetFromButton.Name = "btnGetFromButton";
              this.btnGetFromButton.Size = new System.Drawing.Size(104, 23);
              this.btnGetFromButton.TabIndex = 5;
              this.btnGetFromButton.Text = "Get from Cache";
              this.btnGetFromButton.Click +=
                   new System.EventHandler(this.btnGetFromButton_Click);
              //
              // Form1
              //
              this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
              this.ClientSize = new System.Drawing.Size(488, 133);
              this.Controls.Add(this.btnGetFromButton);
              this.Controls.Add(this.btnPutInCache);
              this.Controls.Add(this.txtValueInCache);
              this.Controls.Add(this.txtValueToPutInCache);
              this.Controls.Add(this.label2);
              this.Controls.Add(this.label1);
              this.Name = "Form1";
              this.Text = "Form1";
              this.ResumeLayout(false);
         }
          #endregion

          private void btnPutInCache_Click(object sender, System.EventArgs e)
         {
              AppMain.Cache.Insert(
                   CACHE_KEY,
                   txtValueToPutInCache.Text,
                   null,
                   Cache.NoAbsoluteExpiration,
                   TimeSpan.FromSeconds( 60 ) );
         }

          private void btnGetFromButton_Click(object sender, System.EventArgs e)
         {
              string value;
              value = AppMain.Cache[ CACHE_KEY ] as string;
              if( null == value )
              {
                   value = "[No value in the cache.]";
              }
              txtValueInCache.Text = value;
         }
     }
}
三、windows form参数传递过程
在Windows 程序设计中参数的传递，同样也是非常的重要的。
这里主要是通过带有参数的构造函数来实现的，

说明：Form1为主窗体，包含控件：文本框textBoxFrm1，多选框checkBoxFrm1和按钮buttonEdit； 
Form2为子窗体，包含控件：文本框textBoxFrm2，多选框checkBoxFrm2和按钮buttonOK，buttonCancel。
当我们新建一个窗体的时候，设计器会生成默认的构造函数： 
     public Form2()
              {
                   InitializeComponent();
            }
它不带参数，既然我们要把Form1中的一些数据传到Form2中去，为什么不在Form2的构造函数里做文章呢？
假设我们要实现使Form2中的文本框显示Form1里textBoxFrm1的值，修改子窗体的构造函数： 
public Form2(string text)         
              {
                   InitializeComponent();
                   this.textBoxFrm2.Text = text; 
            } 增加Form1中的修改按钮点击事件，处理函数如下： 
     private void buttonEdit_Click(object sender, System.EventArgs e)
              {
                   Form2 formChild = new Form2(this.textBoxFrm1.Text);
                   formChild.Show();
              }

我们把this.textBoxFrm1.Text作为参数传到子窗体构造函数，以非模式方式打开，这样打开的formChild的文本框就显示了”主窗体”文本，是不是很简单，接下来我们传一个boolean数据给子窗体。
     Public Form2(string text,bool checkedValue)
         {
              InitializeComponent();
              this.textBoxFrm2.Text = text;
              this.checkBoxFrm2.Checked = checkedValue;
         }

private void buttonEdit_Click(object sender, System.EventArgs e)
         {
              Form2 formChild = new Form2(this.textBoxFrm1.Text,this.checkBoxFrm1.Checked);
              formChild.Show();
         }