在另一个类中启用计时器后调用Timer Tick事件

Question

I must be doing something completely wrong but I cannot figure it out. I have a form and I add in VS a timer control. I also have a class that is watching for an application to start (notepad.exe). When the event arrives it is supposed to enable the timer, set the interval and on each tick do something (like firing a messagebox or changing a label). This seems not to be happening. A look in the code make help someone give me a clue. The code is below:

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");
    }

}

And the watcher class is

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");


    }
}

I noticed two things:

When notepad.exe starts and I have the MessageBox.Show("notpad started"); line commented out the messabox in the timer tick event won't fire. If it is as displayed above it will show me both messageboxes (notepad started and tick). However, the label1.Text will not change no matter what.

I am not sure what I am doing wrong. I am sure it has something to do with how the timer event is handled but I am not sure what I should be doing. Any ideas?

Answer 1

Your code creates a new instance of Monitor. Thus you are not accessing the properties of the Monitor's instance you called eventWatch.WaitForProcessStart() in, so they're not changing. One way to solve this would be an event that is fired as soon as ProcessStarted() is fired. Your code could look like this:

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

It also looks like label1.Text will not change as you are running from a different thread. You would need to run an invoke on that label to update it from ManagementEventWatcher .

Use this class:

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"));