訪問在新線程上創建的對象

Question

我有一個運行新線程以顯示任務欄圖標的應用程序。 現在，我只是想不通如何從主線程調用TaskbarIcon（在新線程上創建）以顯示提示框。

我現在擁有的代碼是：

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);
    }
}

當我嘗試調用'ShowNotification（“ foobar”）;'時 我得到這個例外：

Object reference not set to an instance of an object.

我在'Onload（）'中具有'while（true）{}'的原因是，我需要線程在關閉我的應用程序之前一直運行。

Answer 1

在主線程中，使用以下命令創建一個調度程序：

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

將其傳遞給您的NotificationHelper：

Dispatcher FDispatcher;

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

顯示氣球：

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

Answer 2

您可以嘗試鎖定notifyIcon並檢查是否為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);
            }
        }
    }
}