在另一个类中启用计时器后调用 Timer Tick 事件

Question

我一定是做错了什么，但我想不通。我有一个表格，我在 VS 中添加了一个计时器控件。我还有一个类正在监视应用程序的启动（notepad.exe）。当事件到达时，它应该启用计时器，设置间隔并在每个滴答声上做一些事情（比如触发消息框或更改标签）。这似乎没有发生。看看代码可以帮助有人给我一个线索。代码如下：

public partial class Monitor : Form
{
    EventWatcher eventWatch = new EventWatcher();
    ManagementEventWatcher startWatcher = new ManagementEventWatcher();
    ManagementEventWatcher endWatcher = new ManagementEventWatcher();


    public Monitor()
    {
        InitializeComponent();
        startWatcher  = eventWatch.WatchForProcessStart("notepad.exe");
        endWatcher =   eventWatch.WatchForProcessEnd("notepad.exe");
    }

    private void appTimer_Tick(object sender, EventArgs e)
    {
        label1.Text = "tick";
        MessageBox.Show("Tick");
    }

}

而观察者类是

class EventWatcher
{

    public ManagementEventWatcher WatchForProcessStart(string processName)
    {
        string queryString =
            "SELECT TargetInstance" +
            "  FROM __InstanceCreationEvent " +
            "WITHIN  2 " +
            " WHERE TargetInstance ISA 'Win32_Process' " +
            "   AND TargetInstance.Name = '" + processName + "'";

        // The dot in the scope means use the current machine
        string scope = @"\\.\root\CIMV2";

        // Create a watcher and listen for events
        ManagementEventWatcher watcher = new ManagementEventWatcher(scope, queryString);
        watcher.EventArrived += ProcessStarted;
        watcher.Start();
        return watcher;
    }


    public void ProcessStarted(object sender, EventArrivedEventArgs e)
    {
       Monitor monitor = new Monitor();
       //set timer interval and start time for Monitor class. (form)
       monitor.appTimer.Interval = 5000;
       monitor.appTimer.Enabled = true;

       MessageBox.Show("notepad started");


    }
}

我注意到两件事：

当 notepad.exe 启动并且我将 MessageBox.Show("notpad started"); 行注释掉时，计时器滴答事件中的消息框不会触发。如果如上所示，它将显示两个消息框（记事本已启动和勾选）。但是，label1.Text 无论如何都不会改变。

我不确定我做错了什么。我确信这与如何处理计时器事件有关，但我不确定我应该做什么。有什么想法吗？

Answer 1

您的代码创建了一个新的 Monitor 实例。 因此，您没有访问调用 eventWatch.WaitForProcessStart() 的 Monitor 实例的属性，因此它们不会更改。 解决此问题的一种方法是在 ProcessStarted() 被触发后立即触发一个事件。 您的代码可能如下所示：

class EventWatcher
{

    public event EventHandler<EventArrivedEventArgs> ProcessStarted;

    public ManagementEventWatcher WatchForProcessStart(string processName)
    {
        string queryString =
            "SELECT TargetInstance" +
            "  FROM __InstanceCreationEvent " +
            "WITHIN  2 " +
            " WHERE TargetInstance ISA 'Win32_Process' " +
            "   AND TargetInstance.Name = '" + processName + "'";

        // The dot in the scope means use the current machine
        string scope = @"\\.\root\CIMV2";

        // Create a watcher and listen for events
        ManagementEventWatcher watcher = new ManagementEventWatcher(scope, queryString);
        watcher.EventArrived += OnProcessStarted;
        watcher.Start();
        return watcher;
    }


    protected virtual void OnProcessStarted(object sender, EventArrivedEventArgs e)
    {

        EventHandler<EventArrivedEventArgs> copy = ProcessStarted;
        if (copy != null)
            copy(sender, e); // fire the event

    }
}

public partial class Monitor : Form
{
    EventWatcher eventWatch = new EventWatcher();
    ManagementEventWatcher startWatcher = new ManagementEventWatcher();
    ManagementEventWatcher endWatcher = new ManagementEventWatcher();


    public Monitor()
    {
        InitializeComponent();
        startWatcher  = eventWatch.WatchForProcessStart("notepad.exe");
        startWatcher.ProcessStarted += startWatcher_ProcessStarted; // subscribe to the event
        endWatcher =   eventWatch.WatchForProcessEnd("notepad.exe");
    }

    private void startWatcher_ProcessStarted(object sender, EventArrivedEventArgs e)
    { 
        Monitor monitor = new Monitor();
        //set timer interval and start time for Monitor class. (form)
        monitor.appTimer.Interval = 5000;
        monitor.appTimer.Enabled = true;

        MessageBox.Show("notepad started");
    }

    private void appTimer_Tick(object sender, EventArgs e)
    {
        label1.Text = "tick";
        MessageBox.Show("Tick");
    }

}

Answer 2

看起来label1.Text 不会因为您从不同的线程运行而改变。您需要在该标签上运行调用以从 ManagementEventWatcher 更新它。

使用这个类：

using System;
using System.Windows.Forms;

public static class ControlExtensions
{
    /// <summary> 
    /// Executes the Action asynchronously on the UI thread, does not block execution on the calling thread. 
    /// </summary> 
    /// <param name="control"></param> 
    /// <param name="code"></param> 
    public static void UIThread(this Control @this, Action code)
    {
        if (@this.InvokeRequired)
        {
            @this.BeginInvoke(code);
        }
        else
        {
            code.Invoke();
        }
    }
}

and replace `label1.Text = "tick" ` with

this.UIThread(() => this.label1.Text = "tick"));