Question

我有一个程序有两种形式，表单A可由管理员访问，表单B可供随机用户使用。

表单A用于搜索注册用户列表。表格B用于注册。

表单A具有datagridview，其中包含来自数据库的数据，我希望datagridview在从表单B注册的人之后自动刷新其中的数据...

我想从数据库中获取数据并自动将其放入datagridview而不关闭表单并再次打开它...

抱歉，我还是新来的..请你给我一些建议和例子...... 谢谢......

Answer 1

没有任何代码很难回答你的问题。但通常可以通过简单的事件处理形式解决这类问题。

在您的情况下， FormB 会发布新用户注册的信息。当新用户注册自己时，FormB会检查是否有人注册了自己以通知该事件。 FormA 注册自己以接收事实通知。

在代码中，你在FormB中有这个

public class FormB : Form
{
     public delegate void OnNewUserRegistered(string username)
     public OnNewUserRegistered NewUserRegistered;

     ....

     protected void cmdRegister_Click(object sender, EventArgs e)
     {
         // Code to register the user
         string username = txtUserName.Text;
         ..... etc .....

         // If someone has registered a subscription then call that subscription handler
         if(NewUserRegistered != null)
              NewUserRegistered(username); 

     }
}

根据您的解释，现在最大的问题是FormA在FormB中订阅事件的模式。假设，当FormA加载时，FormB已经打开。您需要搜索FormB的实例

FormA.cs代码

Public FormB RegistrationForm {get; set;}

private void Form_Load(object sender, EventArgs e)
{
   // If FormB is open then get its instance
   this.RegistrationForm = Application.OpenForms.Cast<Form>().OfType<FormB>().FirstOrDefault ();
   if(this.RegistrationForm != null)
   {
       // Subscribe to the registration event in FormB
       RegistrationForm.NewUserRegistered += ANewUserHasBeenRegistered;

       // Subscribe to the closed event of FormB
       RegistrationForm.Closed += FormBHasBeenClosed;
   }

   // Now load the current user list in your grid view.
   LoadUserList(); // this contains the code that initializes the gridView
}    

// this is the subscription method that will be called by the FormB instance
// every time a new user registers with that form
private void ANewUserHasBeenRegistered(string userName)
{
    // Here you have two options.
    // Reload the grid I.E. call LoadUserList();
    // Try to manually add the new user in the current gridview.
    .....
}

// this will be called by the framework when FormB instance closes. 
// It is important to avoid any possibility to reference a destroyed form 
// using the RegistrationForm variable.
private void FormBHasBeenClosed(object sender, FormClosedEventArgs e) 
{
    this.RegistrationForm = null;
}

要解决的最后一点是FormB可以在FormA打开后打开。这可能来自您需要调整的某种menuItem代码：

FormB f = new FormB();

// Search if there is an instance of FormA around
// If found then pass the instance of the FormB to the RegistrationForm public property of FormA
FormA currentFormA = Application.OpenForms.Cast<Form>().OfType<FormA>().FirstOrDefault ();
if(currentFormA != null)
    currentFormA.RegistrationForm = f;

// Allow users to register.....
f.ShowDialog();

如何使用c＃中的datagridview自动刷新数据库中的数据

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