I'm playing around with a tray application. The application runs only in the System Tray and has no Windows Form associated with it. The application uses a ManagementEventWatcher and displays an alert window in certain scenarios.
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new AppContext());
}
...
public class AppContext : ApplicationContext
{
private System.ComponentModel.IContainer _components;
private NotifyIcon _notifyIcon;
private ContextMenuStrip _contextMenu;
private ManagementEventWatcher _regWatcher;
public AppContext()
{
//Initialize context menu & tray icon
_regWatcher = new ManagementEventWatcher(query);
_regWatcher.EventArrived += new EventArrivedEventHandler(_regWatcher_EventArrived);
_regWatcher.Start();
}
void _regWatcher_EventArrived(object sender, EventArrivedEventArgs e)
{
Alert.Show("Alert!", "My Message", someParam);
}
}
...
public class Alert
{
public static void Show(string title, string message, string extraInfo)
{
new Alert(title, message, extraInfo).ShowDialog();
}
private Alert(string title, string message, string extraInfo)
{
InitializeComponent();
this.Icon = Properties.Resources._default;
this.Text = title;
this.label1.Text = message;
this.linkLabel1.Text = extraInfo;
}
}
Interestingly, it doesn't complain about not accessing the UI in a thread-safe way. I suppose because it only exists on this background thread. But later on when the Form tries to access the clipboard, it doesn't work because it is running on an MTA thread. So far, all the similar questions I have found already have a form to call Invoke on, or have the option of using a BackgroundWorker. What is the best way to create and display the Alert Form on the main thread in this case?
Thanks to Idle_Mind's link to Andy Whitfield's blog post I've arrived at a solution. I added a private global SynchronizationContext to the AppContext class. In the constructor I initialize it to an instance of a WindowsFormsSynchronizationContext. Then when the registry watcher's event occurs, I can Post the task back to the main thread.
public class AppContext : ApplicationContext
{
private SynchronizationContext _uiThreadContext;
...
public AppContext()
{
//Initialize context menu & tray icon
_uiThreadContext = new WindowsFormsSynchronizationContext();
_regWatcher = new ManagementEventWatcher(query);
_regWatcher.EventArrived += new EventArrivedEventHandler(_regWatcher_EventArrived);
_regWatcher.Start();
...
}
private void _regWatcher_EventArrived(object sender, EventArrivedEventArgs e)
{
...
_uiThreadContext.Post(new SendOrPostCallback(MyEventHandler), parameters)
}
Related
suppose I have 100 windows form written in C#, is there a way to define a function to be called on the load of any of these forms without needing to change the code of any of these forms, and without inheriting from other form, that is a function that is called automatically whenever a new form is opening?
Thanks,
You can use MessageFilter and intercept the message for the loading of forms. Below is a sample for intercepting forms and then adding an event handler to an event. You can do whatever you need in the event handler.
static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.AddMessageFilter(new TestMessageFilter());
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
}
I know you need to run code just before the load event but for some reason subscribing to the Load event does not fire in the code below. But if you can do it in Activated event, then it will work. Or if you want to do it in another event then just modify the code below and see if that event gets triggered. The code is also keeping a list of all the forms so you don't add multiple handlers for the same event of the same form. When the form is closed, it will remove all the handlers.
[SecurityPermission(SecurityAction.LinkDemand, Flags =
SecurityPermissionFlag.UnmanagedCode)]
public class TestMessageFilter : IMessageFilter
{
private Hashtable forms = new Hashtable();
public bool PreFilterMessage(ref Message m)
{
Control c = Control.FromHandle(m.HWnd);
var form = c as Form;
if (form != null &&
!this.forms.ContainsKey(form))
{
form.Load += Form_Load;
form.Activated += Form_Activated;
form.FormClosed += Form_FormClosed;
this.forms.Add(form, form);
}
return false;
}
private void Form_FormClosed(object sender, FormClosedEventArgs e)
{
if (this.forms.ContainsValue(sender))
{
var f = sender as Form;
f.Activated -= Form_Activated;
f.Load -= Form_Load;
this.forms.Remove(sender);
}
}
private void Form_Activated(object sender, EventArgs e)
{
MessageBox.Show("Form_Activated...");
}
private void Form_Load(object sender, EventArgs e)
{
MessageBox.Show("Form_Load...");
}
}
There is no such other way. You just have to use one of the solutions you've said in your question.
You could use a form factory and implement interception to intercept the OnLoad method or any other virtual method within the Form class.
I created a proof of concept below using Autofac, Castle.Core, and Autofac.Extras.DynamicProxy to intercept the OnLoad method of each form and write to the console before and after the OnLoad method was called on the form.
Form factory passing back Owned. CreateForm(string formName) takes the name of a named Autofac service.
public interface IFormFactory
{
Owned<Form> CreateForm(string formName);
}
public class FormFactory : IFormFactory
{
private readonly IContainer _container;
public FormFactory(IContainer container)
{
_container = container;
}
public Owned<Form> CreateForm(string formName)
{
return _container.ResolveNamed<Owned<Form>>(formName);
}
}
The interceptor below will be called every time a virtual method on the form. I added a check for OnLoad however you can intercept and call for other virtual methods as well.
public class FormInterceptor : IInterceptor
{
public void Intercept(IInvocation invocation)
{
bool isFormOnLoad = invocation.InvocationTarget is Form && invocation.Method.Name.Equals("OnLoad");
if(isFormOnLoad)
{
Console.WriteLine("Before OnLoad");
}
invocation.Proceed();
if(isFormOnLoad)
{
Console.WriteLine("After OnLoad");
}
}
}
Register your interceptor, forms, and factory taking care to used named services. The names will used to create the forms in the factory method.
static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
var builder = new ContainerBuilder();
builder.RegisterType<FormInterceptor>();
Castle.DynamicProxy.Generators.AttributesToAvoidReplicating.Add<System.Security.Permissions.UIPermissionAttribute>();
// Register your forms
builder.RegisterType<frmMain>()
.Named<Form>("frmMain")
.EnableClassInterceptors()
.InterceptedBy(typeof(FormInterceptor));
builder.RegisterType<frmSubForm>()
.Named<Form>("frmSubForm")
.EnableClassInterceptors()
.InterceptedBy(typeof(FormInterceptor));
FormFactory = new FormFactory(builder.Build());
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(FormFactory.CreateForm("frmMain").Value);
}
public static IFormFactory FormFactory { get; set; }
}
Below is an example of creating and showing a test form within the main form:
private void button1_Click(object sender, EventArgs e)
{
using (var subForm = Program.FormFactory.CreateForm("frmSubForm").Value)
{
subForm.ShowDialog(this);
}
}
I have a windows form application which is supposed to show a splash screen with a label field that I want to update as the main form (called welcome.cs) loads in the background. The splash screen shows & hides just fine, but the label doesn't update.
I've done a lot of research but haven't quite found the solution.
Program.cs
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
using (new SingleGlobalInstance(1000))
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
SplashScreen splashscreen = new SplashScreen();
splashscreen.ShowSplashScreen();
Welcome welcome = new Welcome(splashscreen); //Takes some time to load
splashscreen.CloseForm();
Application.Run(welcome);
}
}
Splashscreen.cs
public partial class SplashScreen : Form
{
//Delegate for cross thread call to close
private delegate void CloseDelegate();
private delegate void UpdateStatusDelegate(string status);
private static SplashScreen splashScreen;
private Thread thread = null;
public SplashScreen()
{
InitializeComponent();
}
public void ShowSplashScreen()
{
// Make sure it is only launched once.
if (splashScreen != null)
return;
thread = new Thread(ShowForm);
thread.IsBackground = true;
thread.SetApartmentState(ApartmentState.STA);
thread.Start();
}
static private void ShowForm()
{
splashScreen = new SplashScreen();
Application.Run(splashScreen);
}
public void CloseForm()
{
splashScreen.Invoke(new CloseDelegate(CloseFormInternal));
}
static private void CloseFormInternal()
{
splashScreen.Close();
}
public void UpdateStatus(string status)
{
splashScreen.Invoke(new UpdateStatusDelegate(UpdateStatusInternal), status);
}
private void UpdateStatusInternal (string status)
{
if (splashScreen != null && splashScreen.IsHandleCreated)
{
lblStatus.Text = status;
}
}
}
Welcome.cs
public Welcome(Splashscreen splashscreen)
{
InitializeComponent();
//Code to log the user into the system
splashScreen.UpdateStatus("Logging in...");
//my expectation is that UpdateStatus call will update the label displayed on the splash screen but it doesn't.
//Do more stuff.....
}
Does it have something to do with multi-threading or is it because im creating a new instance of splashscreen in welcome.cs before calling UpdateStatus? How would I get around this?
You could do the following
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
string[] args = Environment.GetCommandLineArgs();
// Creates the Splash
splash = new FrmSplash();
//Opens the Splash in a new Thread, this way any gifs, progress bars, lablels changes will work because the main thread isnt blocked
var t = Task.Factory.StartNew(() =>
{
splash.ShowDialog();
});
while (!splash.Created) // wait the splash screen form load process
System.Threading.Thread.Sleep(300);
UpdateSplashMessage("Loading the program... Please wait");
// Some slow initialization code.
// ...
//Close splash screen
CloseSplash();
Application.Run(args);
}
static void CloseSplash()
{
splash.Invoke(new MethodInvoker(() =>
{
splash.Close(); // Closes the splash that is running in the other thread
}));
}
static void UpdateSplashMessage(string msg)
{
splash.Invoke(new MethodInvoker(() =>
{
splash.AtualizarMensagem(msg);
}));
}
Note that you will need to create a method called AtualizarMensagem(string str) in your splash screen form, like this
public void AtualizarMensagem(string novaMsg)
{
lblCarregando.Text = novaMsg;
}
I have this code in my "useful snnipets" folder, it always works for me.
Hope this helps.
I've searched and can't find a solution that helps me get text from a thread running in a separate class, back to a listbox on the form that created the thread.
Basically I have a class that holds a "test", it is called in it's own thread from a test window. What I want to be able to do is add text to a listbox on the main form to let the user know what is going on with a test. All the examples I can find on Invoke show how to do it within the same class.
Where I start the thread:
PermeabilityTest Run_Test = new PermeabilityTest();
public Thread WorkerThread;
private void button2_Click(object sender, EventArgs e)
{
//enable timer for test duration display
timer1.Enabled = true;
//create and start new thread.
WorkerThread = new Thread(Run_Test.RunTest);
WorkerThread.Start();
}
Here is my class that actually does the work, where I need to get text back to a listbox on a separate form from.
public class PermeabilityTest
{
//volatile alerts the compiler that it will be used across threads.
private volatile bool aborted;
public void RequestStop()
{
//handle saving data file here as well.
aborted = true;
}
public void RunTest()
{
//reference the comms class so we can communicate with the machine
PMI_Software.COMMS COM = new COMMS();
//some test stuffs here
int x = 0;
while( x < 100 && !aborted)
{
System.Diagnostics.Debug.Write("Well here it is, running it's own thread." + Environment.NewLine);
COM.Pause(1);
}
}
}
I would appreciate any one who could help me understand how to get some text back to a listbox on the same form that has the button which starts the thread.
Option 1: (Preffered) Add an event on PermeabilityTest and register on that event in your main form.
Then modify the content of your List box from within your main form.
Example:
Your main form:
PermeabilityTest Run_Test = new PermeabilityTest();
public Thread WorkerThread;
public form1()
{
// Register on the Progress event
Run_Test.Progress += Run_Test_Progress;
}
void Run_Test_Progress(string message)
{
if(listBox.InvokeRequired)
{
// Running on a different thread than the one created the control
Delegate d = new ProgressEventHandler(Run_Test_Progress);
listBox.Invoke(d, message);
}
else
{
// Running on the same thread which created the control
listBox.Items.Add(message);
}
}
private void button2_Click(object sender, EventArgs e)
{
//enable timer for test duration display
timer1.Enabled = true;
//create and start new thread.
WorkerThread = new Thread(Run_Test.RunTest);
WorkerThread.Start();
}
new Delegate:
public delegate void ProgressEventHandler(string message);
Modified PermeabilityTest class:
public class PermeabilityTest
{
//volatile alerts the compiler that it will be used across threads.
private volatile bool aborted;
public event ProgressEventHandler Progress;
public void RequestStop()
{
//handle saving data file here as well.
aborted = true;
}
public void RunTest()
{
//reference the comms class so we can communicate with the machine
PMI_Software.COMMS COM = new COMMS();
//some test stuffs here
int x = 0;
while (x < 100 && !aborted)
{
// Report on progress
if(Progress != null)
{
Progress("This message will appear in ListBox");
}
System.Diagnostics.Debug.Write("Well here it is, running it's own thread." + Environment.NewLine);
COM.Pause(1);
}
}
}
Option 2:
You could make PermeabilityTest an inner class of your main form, and by doing so, allow it to access private members of your main form.
Then you need to pass a reference of your main form to the constructor of PermeabilityTest and keep it as a member.
Option 3:
pass your list box to the constructor of PermeabilityTest
Don't forget to use Invoke on your control since you are running from a different thread.
I created two separate Windows Forms applications in C# that use MSMQ for communicating. Here's how it works, it looked simple enough though:
App1 sends a details request to App2.
App2 creates an event to open the window.
App2 opens a "details" window.
The only problem I have is that when received the message, the "details" window freezes after appearing.
As I handle MSMQ messages handling in an object that uses threads, I suspect the problem comes from there... But I have no experience in handling MSMQ messages or specific events handling between parts of an application.
Here's part of the code I use for App2:
/*Class declared in the Core namespace*/
public class TaskMessageQueueHandler
{
public TaskMessageQueueHandler()
{
this.Start();
}
private Thread m_thread;
private ManualResetEvent m_signal;
public event System.EventHandler messageReceived;
public void Start()
{
m_signal = new ManualResetEvent(false);
m_thread = new Thread(MSMQReceiveLoop);
m_thread.Start();
}
public void Stop()
{
m_signal.Set();
}
protected virtual void SendEvent(object sender, EventArgs e)
{
if (messageReceived != null)
messageReceived(this.message, e);
}
public string message;
private void MSMQReceiveLoop()
{
bool running = true;
MessageQueue queue = new MessageQueue(#".\Private$\queue1");
while (running)
{
try
{
var message = queue.Receive();
message.Formatter = new XmlMessageFormatter(new String[] { "System.String,mscorlib" });
this.message = message.Body.ToString();
string m = this.message;
SendEvent(m, System.EventArgs.Empty);
if (m_signal.WaitOne(10))
{
running = false;
}
}
catch
{
Console.WriteLine("ERROR");
running = false;
}
}
}
}
/*Main process, in the Program namespace*/
[...]
Core.TaskMessageQueueHandler tmqh = new Core.TaskMessageQueueHandler();
EventListener el = new EventListener();
tmqh.messageReceived += new System.EventHandler(el.ShowDetails);
[...]
/* Class in the Program namespace */
class EventListener
{
public void ShowDetails(object sender, EventArgs e)
{
int numero = int.Parse(sender as string);
Details details = new Details(numero);
details.Show();
}
}
Where did I go wrong? Where did I go right?
Thanks a lot,
Stephane.P
EDIT: if the MSMQ handler is stopped with Stop() anywhere around the event sending, the details window appears then disappears right away...
EDIT2: After the workaround given by Slugart, I managed to make this work:
class EventListener
{
Main control;
public EventListener(Main main)
{
control = main;
}
public void ShowDetails(object sender, EventArgs e)
{
int numero = int.Parse(sender as string);
control.Invoke((Action)(() => ShowDetails(numero)));
}
private void ShowDetails(int numero)
{
Details details = new Details(numero);
details.Show();
}
}
Which is used like:
Core.TaskMessageQueueHandler tmqh = new Core.TaskMessageQueueHandler();
EventListener el = new EventListener(this);
tmqh.messageReceived += new System.EventHandler(el.ShowDetails);
You're creating and displaying a form Details on a thread other than the main GUI thread and not an STA thread at that.
Your EventListener should have a reference to a running form (your main form perhaps) and then call form.Invoke() on it.
class EventListener
{
Control control; // A valid running winforms control/form created on an STA thread.
public void ShowDetails(object sender, string message)
{
int numero = int.Parse(message);
control.Invoke(() => ShowDetails(numero))
}
private void ShowDetails(int numero)
{
Details details = new Details(numero);
details.Show();
}
}
Also sending your event data as the sender is not really following the Event pattern that has been put in front of you. You want to use the EventArgs parameter for this, use the EventHandler delegate (EventHandler in your case).
I've been trying to learn delegates.I just created a button,label and checkbox. If I click checkbox, the time format changes. If i click the button , i print the date accordingly. However when trying to use asynchromous delegate i.e., to use another thread, i am stuck with an error
public delegate void AsyncDelegate(bool seconds);
public partial class Form1 : Form
{
AsyncDelegate ad;
TimeZ t = new TimeZ();
public Form1()
{
InitializeComponent();
}
private void btn_async_Click(object sender, EventArgs e)
{
ad = new AsyncDelegate(t.GetTime);
AsyncCallback acb = new AsyncCallback(CB);
if (chk_sec.Checked)
{
ad.BeginInvoke(true, acb, null);
}
else
ad.BeginInvoke(false, acb, null);
}
public void CB(IAsyncResult ar)
{
t.Tim = ar.ToString();
ad.EndInvoke(ar);
lbl_time.Text = t.Tim;
}
and in another class library i get Timez used above. I add a reference of it in the project
public class TimeZ
{
private string tim;
public string Tim
{
get
{
return tim;
}
set
{
tim = value;
}
}
public string GetTime(bool seconds)
{
if (seconds)
{
return DateTime.Now.ToLongTimeString();
}
else
return DateTime.Now.ToShortTimeString();
}
}
However i get this error when i run the program:
Cross-thread operation not valid: Control 'lbl_time' accessed from a thread other than
the thread it was created on.
Can u help me out on how to solve this?
You cannot access forms and controls properties and methods from a thread that is not the form thread.
In windows, each window is bound to the thread that created it.
You can do that only with Control.BeginInvoke or the more useful System.Threading.SynchronizationContext class.
See http://msdn.microsoft.com/it-it/library/system.threading.synchronizationcontext(v=vs.95).aspx
See http://msdn.microsoft.com/it-it/library/0b1bf3y3(v=vs.80).aspx
It means, you have to post through synchronization context for example another async delegate in form thread.
public partial class Form1 : Form
{
AsyncDelegate ad;
TimeZ t = new TimeZ();
// Our synchronization context
SynchronizationContext syncContext;
public Form1()
{
InitializeComponent();
// Initialize the synchronization context field
syncContext = SynchronizationContext.Current;
}
private void btn_async_Click(object sender, EventArgs e)
{
ad = new AsyncDelegate(t.GetTime);
AsyncCallback acb = new AsyncCallback(CB);
if (chk_sec.Checked)
{
ad.BeginInvoke(true, acb, null);
}
else
{
ad.BeginInvoke(false, acb, null);
}
}
public void CB(IAsyncResult ar)
{
// this will be executed in another thread
t.Tim = ar.ToString(); // ar.ToString()???? this will not give you the time for sure! why?
ad.EndInvoke(ar);
syncContext.Post(delegate(object state)
{
// This will be executed again in form thread
lbl_time.Text = t.Tim;
}, null);
}
I don't know why you need an asynchronous callback to print time however :) really don't know why, thinking it is just some test code.