如何使用backgroundworker更新GUI？

Question

我花了一整天的时间试图让我的应用程序使用线程,但没有运气.我已经阅读了很多关于它的文档,我仍然会遇到很多错误,所以我希望你能帮助我.

我有一个耗时的方法,它调用数据库并更新GUI.这必须一直发生(或大约每30秒).

public class UpdateController
{
    private UserController _userController;

    public UpdateController(LoginController loginController, UserController userController)
    {
        _userController = userController;
        loginController.LoginEvent += Update;
    }

    public void Update()
    {
        BackgroundWorker backgroundWorker = new BackgroundWorker();
        while(true)
        {
            backgroundWorker.DoWork += new DoWorkEventHandler(backgroundWorker_DoWork);
            backgroundWorker.RunWorkerAsync();
        }     
    }

    public void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
    {
        _userController.UpdateUsersOnMap();
    }
}

使用这种方法我得到一个例外,因为后台工作者不是和STA线程(但从我可以理解这是我应该使用的).我试过一个STA线程,并给出了其他错误.

我认为问题是因为我在进行数据库调用时尝试更新GUI(在后台线程中).我应该只进行数据库调用,然后以某种方式它应该切换回主线程.在主线程执行后,它应该返回后台线程,依此类推.但我看不出怎么做.

应用程序应在数据库调用后立即更新GUI.Firering事件似乎不起作用.背景线程只是输入它们.

编辑:

一些非常好的答案:)这是新的代码:

public class UpdateController{
private UserController _userController;
private BackgroundWorker _backgroundWorker;

public UpdateController(LoginController loginController, UserController userController)
{
    _userController = userController;
    loginController.LoginEvent += Update;
    _backgroundWorker = new BackgroundWorker();
    _backgroundWorker.DoWork += backgroundWorker_DoWork;
    _backgroundWorker.RunWorkerCompleted += backgroundWorker_RunWorkerCompleted;
}

public void _backgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    _userController.UpdateUsersOnMap();
}

public void Update()
{   
    _backgroundWorker.RunWorkerAsync();
}

void backgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    //UI update
    System.Threading.Thread.Sleep(10000);
    Update();
}

public void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
    // Big database task
}

}

但是我怎么能每隔10秒运行一次呢？System.Threading.Thread.Sleep(10000)将使我的GUI冻结,而Update()中的while(true)循环按建议给出异常(Thread太忙).

Answer 1

您需要声明并配置BackgroundWorker一次 - 然后在循环中调用RunWorkerAsync方法...

public class UpdateController
{
    private UserController _userController;
    private BackgroundWorker _backgroundWorker;

    public UpdateController(LoginController loginController, UserController userController)
    {
        _userController = userController;
        loginController.LoginEvent += Update;
        _backgroundWorker = new BackgroundWorker();
        _backgroundWorker.DoWork += new DoWorkEventHandler(backgroundWorker_DoWork);
        _backgroundWorker.ProgressChanged += new ProgressChangedEventHandler(backgroundWorker_ProgressChanged);
        _backgroundWorker.WorkerReportsProgress= true;
    }

    public void Update()
    {
         _backgroundWorker.RunWorkerAsync();    
    }

    public void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
    {
        while (true)
        {
        // Do the long-duration work here, and optionally
        // send the update back to the UI thread...
        int p = 0;// set your progress if appropriate
        object param = "something"; // use this to pass any additional parameter back to the UI
        _backgroundWorker.ReportProgress(p, param);
        }
    }

    // This event handler updates the UI
    private void backgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        // Update the UI here
//        _userController.UpdateUsersOnMap();
    }
}

Answer 2

您必须使用Control.InvokeRequired属性来确定您是否在后台线程上.然后,您需要通过Control.Invoke方法调用修改UI的逻辑,以强制在主线程上进行UI操作.您可以通过创建委托并将其传递给Control.Invoke方法来完成此操作.这里的问题是你需要从Control派生的一些对象来调用这些方法.

编辑:当另一个用户发布时,如果您可以等到BackgroundWorker.Completed事件来更新您的UI,那么您可以订阅该事件并直接调用您的UI代码.在主应用程序线程上调用BackgroundWorker_Completed.我的代码假设您希望在操作期间进行更新.我的方法的一个替代方案是订阅BwackgroundWorker.ProgressChanged事件,但我相信在这种情况下你仍然需要调用Invoke来更新你的UI.

例如

public class UpdateController
{
    private UserController _userController;        
    BackgroundWorker backgroundWorker = new BackgroundWorker();

    public UpdateController(LoginController loginController, UserController userController)
    {
        _userController = userController;
        loginController.LoginEvent += Update;
    }

    public void Update()
    {                        
         // The while loop was unecessary here
         backgroundWorker.DoWork += new DoWorkEventHandler(backgroundWorker_DoWork);
         backgroundWorker.RunWorkerAsync();                 
    }

    public delegate void DoUIWorkHandler();


    public void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
    {
       // You must check here if your are executing on a background thread.
       // UI operations are only allowed on the main application thread
       if (someControlOnMyForm.InvokeRequired)
       {
           // This is how you force your logic to be called on the main
           // application thread
           someControlOnMyForm.Invoke(new             
                      DoUIWorkHandler(_userController.UpdateUsersOnMap);
       }
       else
       {
           _userController.UpdateUsersOnMap()
       }
    }
}

Answer 3

你应该删除while(true),你正在添加无限的事件处理程序并无限次地调用它们.