访问在新线程上创建的对象

Question

我有一个运行新线程以显示任务栏图标的应用程序。 现在，我只是想不通如何从主线程调用TaskbarIcon（在新线程上创建）以显示提示框。

我现在拥有的代码是：

public class NotificationHelper
{
    private TaskbarIcon notifyIcon { get; set; }

    public NotificationHelper()
    {
        Thread thread = new Thread(OnLoad);
        thread.SetApartmentState(ApartmentState.STA); //Set the thread to STA
        thread.Start();
    }

    public void ShowNotification(string text)
    {
        notifyIcon.ShowBalloonTip("Demo", text, notifyIcon.Icon);
    }

    public void OnLoad()
    {
        notifyIcon = new TaskbarIcon();
        notifyIcon.Icon =
            new Icon(@".\Icon\super-man-icon.ico");
        //notifyIcon.ToolTipText = "Left-click to open popup";
        notifyIcon.Visibility = Visibility.Visible;

        while (true)
        {
            Thread.Sleep(1000);
        }
    }

    private void ShowBalloon()
    {
        notifyIcon.ShowBalloonTip("Demo", Message, notifyIcon.Icon);
    }
}

当我尝试调用'ShowNotification（“ foobar”）;'时 我得到这个例外：

Object reference not set to an instance of an object.

我在'Onload（）'中具有'while（true）{}'的原因是，我需要线程在关闭我的应用程序之前一直运行。

Answer 1

在主线程中，使用以下命令创建一个调度程序：

Dispatcher dispatcher = System.Windows.Threading.Dispatcher.CurrentDispatcher;

将其传递给您的NotificationHelper：

Dispatcher FDispatcher;

public NotificationHelper(Dispatcher ADispatcher)
{
     FDispatcher = ADispatcher;
     //...
}

显示气球：

private void ShowBalloon()
{
    FDispatcher.invoke(new Action(() => {
        notifyIcon.ShowBalloonTip("Demo", Message, notifyIcon.Icon);
    }));
}

Answer 2

您可以尝试锁定notifyIcon并检查是否为null，如下所示：

public class NotificationHelper 
{
    private readonly object notifyIconLock = new object();
    private TaskbarIcon notifyIcon { get; set; }      

    public NotificationHelper()     
    {         
        Thread thread = new Thread(OnLoad);         
        thread.SetApartmentState(ApartmentState.STA); //Set the thread to STA         
        thread.Start();
    }

    public void ShowNotification(string text)
    {
        lock (notifyIconLock)
        {
            if (notifyIcon != null)
            {
                notifyIcon.ShowBalloonTip("Demo", text, notifyIcon.Icon);
            }
        }
    }

    public void OnLoad()
    {
        lock (notifyIconLock)
        {
            notifyIcon = new TaskbarIcon();
            notifyIcon.Icon =
                new Icon(@".\Icon\super-man-icon.ico");
            //notifyIcon.ToolTipText = "Left-click to open popup";
            notifyIcon.Visibility = Visibility.Visible;
        }
    }

    private void ShowBalloon()
    {
        lock (notifyIconLock)
        {
            if (notifyIcon != null)
            {
                notifyIcon.ShowBalloonTip("Demo", Message, notifyIcon.Icon);
            }
        }
    }
}