Re: Delegates throwing Null Exception - C# Discussion Boards

Judah Gabriel Himango13-Jun-06 9:39

13-Jun-06 9:39

FYI, you can utilize the System.Windows.Forms.WindowsFormsSynchronizationContext object to raise events on the UI thread from your class without having to "entangle" to two objects. You don't even have to entangle your object with Windows forms either; just have it accept any old SynchronizationContext. For Windows Forms apps, you can pass in a WindowsFormsSynchronizationContext and the class then doesn't have to be specific to Windows Forms. Cool | :cool:

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Judah Himango

Re: Delegates throwing Null Exception

Dustin Metzgar13-Jun-06 10:15

Dustin Metzgar

13-Jun-06 10:15

Looks pretty cool. My one complaint being that you're stuck with the SendOrPostCallback delegate which only takes one object. I'm not really sure you can call it raising an event either because it doesn't technically raise any events. But this is definitely a nice new tool that I'll want to experiment with in the future.

Logifusion[^]

Re: Delegates throwing Null Exception

Judah Gabriel Himango13-Jun-06 12:50

Judah Gabriel Himango

13-Jun-06 12:50

It really addresses a particular problem that encompasses events: SynchronizationContext are meant for doing things (such as calling methods, raising events, etc.) on a particular thread by either Posting (which corresponds to BeginInvoke for Windows Forms) or Sending (which corresponds to Invoke for Windows Forms).

Thus, you *could* make a library that can dispatch events on a UI thread without tying your library to that control, or even to Windows Forms, for that matter. For example:

class MyCrazyLib
{
   private SynchronizationContext syncContext;
   public event EventHandler WorkProgressed;

   public MyCrazyLib(SynchronizationContext eventRaisingSync)
   {
      this.syncContext = eventRaisingSync;
   }

   void DoWorkInBackground()
   {
      ThreadPool.QueueUserWorkItem(MyWorkMethod);
   }

   void MyWorkMethod(object state)
   {
      // Pretend we do some work here...
      ...

      // Now raise the event using our synchronization context.
      this.syncContext.Post(delegate(object state)
      {
         this.WorkProgressed(someSender, EventArgs.Empty);
      });
   }
}

There you've got yourself a library that *can* raise events on any thread, UI thread or otherwise. To use this with Windows Forms, you can simply do:

// While on the UI thread.
MyCrazyLib lib = new MyCrazyLib(WindowsFormsSynchronizationContext.Current); // We want to raise events on the current UI thread
lib.WorkProgressed += MyHandler;
lib.DoWorkInBackground();

...

void MyHandler(object sender, EventArgs e)
{
   // This will be called on the UI thread! No Invoke required. :)
}

Tech, life, family, faith: Give me a visit.
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Judah Himango

Re: Delegates throwing Null Exception

Dustin Metzgar13-Jun-06 15:31

Dustin Metzgar

13-Jun-06 15:31

Excellent! The name SynchronizationContext gave me pause because it makes me wonder if it's actually going to still let me do my work asynchronously. I can see from your example that it works just fine. Thanks for showing me this!

Logifusion[^]

Re: Delegates throwing Null Exception

Dustin Metzgar13-Jun-06 7:43

Dustin Metzgar

13-Jun-06 7:43

SearchComplete is an event, not a delegate. If you want to fire the event, get rid of Parent.Invoke and use if (SearchComplete != null) SearchComplete(this, new EventArgs()); Or whatever you have to pass into your ProcessingCompleteDelegate.

Logifusion[^]

Re: Delegates throwing Null Exception

gantww13-Jun-06 7:49

gantww

13-Jun-06 7:49

Whoops. I didn't even see that. Try his suggestion first. You want to raise the event on your class, not on the form. In the handler for the event (on the form), check for InvokeRequired. If it is required, then you'll have to do call this.Invoke to get it back onto your UI thread.

Re: Delegates throwing Null Exception

acezrwild81713-Jun-06 7:54

acezrwild817

13-Jun-06 7:54

I used the wrong wording before. You are correct about it being an event, but it doesn't work either way. I have to use invoke because i will be accessing the controls of another form in another thread when i make this call. I need the event to not have the value null because i need to fire it. For whatever reason when I register ArtifactSearch for its events before I start the thread, they are not staying registered.

Re: Delegates throwing Null Exception

Dustin Metzgar13-Jun-06 8:04

Dustin Metzgar

13-Jun-06 8:04

You're thinking about this backwards. The event should not care anything about what's listening to it. It doesn't care what thread the listener is in. The event should just fire. It is the job of the listener to get itself back into the main thread. You have a listener in MainForm, but when you interact with anything in MainForm, you're going to have to do it through the use of Invoke. This means you'll have to write delegates for MainForm, but luckily anonymous methods will make this easier.

Logifusion[^]

Re: Delegates throwing Null Exception

acezrwild81713-Jun-06 8:13

acezrwild817

13-Jun-06 8:13

I don't understand what the other guy was saying about lock statements... never used them. Is this the solution?

Re: Delegates throwing Null Exception

gantww13-Jun-06 8:21

gantww

13-Jun-06 8:21

In this case, I think you can get away without having to use them. Check out my comments above for more info.

Re: Delegates throwing Null Exception

nicknotyet13-Jun-06 9:28

nicknotyet

13-Jun-06 9:28

Once you have the delegate vs event thing straightened out, here are some articles on accessing Forms from non-UI threads.

http://www.csharphelp.com/archives2/archive375.html

http://msdn2.microsoft.com/en-us/library/ms171728(VS.80,d=ide).aspx

http://weblogs.asp.net/justin_rogers/articles/126345.aspx

Custom Tools

gantww13-Jun-06 7:27

gantww

13-Jun-06 7:27

Hello all,
I've been looking into what is required to write a custom tool for Visual Studio 2005. Specifically, what I want to do is write a tool that can take an XML file containing a connection string and generate a strongly-typed wrapper around the database. Basically, the idea here is to make it so that I have easy intellisense access to the names of tables, views, fields, stored procedures, parameters, etc. so that I will stop misspelling them and to reduce the problems caused by changing the database schema. That and I want to play with the CodeDOM in a useful fashion.

So, my question is: Has anyone here implemented a custom tool and had it work in Visual Studio 2005? I know I could use a custom build provider, but I intend to be using this in business layer code. My understanding is that build providers don't work in anything other than ASP.NET.

Re: Custom Tools

gantww13-Jun-06 7:51

gantww

13-Jun-06 7:51

Err....

I meant to say non-web code. It will actually be the data access layer, not the business layer. D'Oh! | :doh:

Delay of MDI [modified]

mohamed fahmy13-Jun-06 6:57

mohamed fahmy

13-Jun-06 6:57

hello Everyone,
i wrote an application with MDI Forms and have a problem which didn't know it's reason Sigh | :sigh:

,
which is delaying time when navigating between forms and thats all .
thanx

-- modified at 12:58 Tuesday 13th June, 2006

ToolTip Bubble Incorrect location!

cnich2313-Jun-06 6:30

cnich23

13-Jun-06 6:30

.NET 2.0

I am using the Tooltip control to notify user's of input error. The tooltip is set as a bubble tip. When a call the the Show method, the tooptip bubble does not display correctly. The buble pointer will be offset from the control.

Now if I call the show method twice in a row with the same control passed then it will display correcty.

What is causing the tooltip to not be displayed correctly when in bubble form?

Console.WriteLine ?

AlexKiat13-Jun-06 6:13

AlexKiat

13-Jun-06 6:13

Hi, can anyone tell me what's the difference between console.write and trace.write ?

I'm currently facing problem to trace the output of the Class file. Other than try catch, any other way to easily see the whole process log ?

Help, I'm not able to trace the class output... Am using visual webdev2005, thnks.

Re: Console.WriteLine ?

Josh Smith13-Jun-06 8:29

Josh Smith

13-Jun-06 8:29

By default the Listeners collection associated with the Trace class contains only one TraceListener. That listener writes to the standard output stream (the same stream that Console writes to). You can add in different TraceListener objects to the Listeners property, which will allow your trace messages to be redirected to whatever backing stores you desire.

Josh

Re: Console.WriteLine ?

Elina Blank13-Jun-06 9:59

Elina Blank

13-Jun-06 9:59

Trace class is part of the System.Diagnostics namespace which provides classes that allow you to interact with system processes, event logs, and performance counters
Trace.WriteLine: writes information about the trace to the trace listeners in the Listeners collection.

Console: represents the standard input, output, and error streams for console applications

Console.WriteLIne: Writes the specified data, followed by the current line terminator, to the standard output stream

Source: Microsoft Visual Studio Documentation

Sincerely,
Elina

Life is great!!!
Enjoy every moment of it! Blush | :O

how to close an application from another form?

donkaiser13-Jun-06 5:49

donkaiser

13-Jun-06 5:49

Hello,
I have 2 forms. once i make my choice of the application i wanna run Form1 is hidden and form2 is showing up. if i want to terminate my program in Form2, Form is still running. I don't wanna instantiate Form1 again in Form2 to close Form1. it's gonna create a new Form1 right?
what is the best way to terminate both forms from Form2?

Thank you

Donkaiser

Re: how to close an application from another form?

led mike13-Jun-06 5:57

led mike

13-Jun-06 5:57

Application.Exit()

Re: how to close an application from another form?

donkaiser13-Jun-06 5:58

donkaiser

13-Jun-06 5:58

What i mean is that when i do application.exit() on Form2, the IDE still running in debugging mode.
Is it because of Form1 which is hidden and i didn't close it?

Donkaiser

Re: how to close an application from another form?

Roy Heil14-Jun-06 3:38

Roy Heil

14-Jun-06 3:38

Really? Application.Exit() should have closed the application, not just Form2. Hiding Form1 should not make a difference. Form2 isn't a separate application that you are spawning from the Form1 application, is it?

Roy.

How to print tabs in a textbox

WebMaster13-Jun-06 5:46

WebMaster

13-Jun-06 5:46

Hi. Im writing a windows application in C# and it has to be able to send the contents of a textbox to the printer. I'm using a StringReader to do this.

My only problem right now is the textox does not send tabs to the printer. I use \t to format the data the way I like and it displays fine on screen but when it gets sent to the printer its like the \t is ignored and all the data is crunched together.

Any ideas?

Thanks

DataSets: SQL Statement versus Relations.Add

leckey13-Jun-06 5:40

leckey

13-Jun-06 5:40

I am working with a dataset in which I need to access about 11 tables with lots of child/parent relations. I was going to do one large SQL statement but would using Relations.Add be better? Is one considered better than another?

Browser Helper Object, problem with SHDocVw.DWebBrowserEvents2_Event.DocumentComplete

klepa11235813-Jun-06 5:02

klepa112358

13-Jun-06 5:02

I'm writing Browser Helper Object (IExplorer plug-in) in C#, Microsoft VS 2005, Framwork 2.0.
1. I implement interface IObjectWithSite and add event handler for events SHDocVw.DWebBrowserEvents2_Event.DocumentComplete and SHDocVw.DWebBrowserEvents2_Event.OnQuit in function SetSite :
[System.Runtime.InteropServices.ComImport, System.Runtime.InteropServices.Guid( "FC4801A3-2BA9-11CF-A229-00AA003D7352" ), System.Runtime.InteropServices.InterfaceType( System.Runtime.InteropServices.ComInterfaceType.InterfaceIsIUnknown )]
public interface IObjectWithSite
{
void SetSite( [System.Runtime.InteropServices.In, System.Runtime.InteropServices.MarshalAs( System.Runtime.InteropServices.UnmanagedType.IUnknown )] object pUnkSite );
void GetSite( [System.Runtime.InteropServices.In] ref System.Guid riid, [System.Runtime.InteropServices.Out] System.IntPtr ppvSite );
}
[System.Runtime.InteropServices.ComVisible( true ), System.Runtime.InteropServices.Guid( "C06B3B91-769A-42d5-8BCD-CF70F8589FBA" ), System.Runtime.InteropServices.ClassInterface( System.Runtime.InteropServices.ClassInterfaceType.None )]
public class DOMPeek : IObjectWithSite
{
void IObjectWithSite.SetSite( object pUnkSite )
{
if(m_IUnkSite != null)
{
System.Runtime.InteropServices.Marshal.ReleaseComObject( m_IUnkSite );
}
m_IUnkSite = pUnkSite;
try
{
SHDocVw.DWebBrowserEvents2_Event WebBrowserEvents = (SHDocVw.DWebBrowserEvents2_Event)m_IUnkSite;
WebBrowserEvents.DocumentComplete += new SHDocVw.DWebBrowserEvents2_DocumentCompleteEventHandler( OnDocumentComplete );
WebBrowserEvents.OnQuit += new SHDocVw.DWebBrowserEvents2_OnQuitEventHandler( OnQuit );
}
catch // cast or no such interface exception
{
}
return;
}
void IObjectWithSite.GetSite( ref System.Guid riid, System.IntPtr ppvSite )
{
}
2. Implement event handlers OnQuit and DocumentComplete
void OnQuit()
{
System.Windows.Forms.MessageBox.Show( "OnQuit" );
}
void OnDocumentComplete( object pDispatch, ref object VariantURL )
{
System.Windows.Forms.MessageBox.Show( "OnDocumentComplete : " + VariantURL );
}
3. I register the object DOMPeek as Browser Helper Object in windows register.

Then I run IExplorer and see the messageBox "OnDocumentComplete : about:blank". Then I close IE window and see the messageBox "OnQuite".

The problem consist in that I take this result only in MSWindosw2003sp1 (server) with MS VS2005 installed. In MSWindowsXPsp2 without any updates, without MS VS2005, but with all Framework installed I didn't see the messageBox "OnDocumentComplete : about:blank", but see the messageBox "OnQuit". What's problem??? What updates need for correct working in MSWindowsXPsp2???
Then I try to install all updates for MSWindowsXPsp2 from Microsoft site and again didn't see the messageBox "OnDocumentComplete : about:blank", but see the messageBox "OnQuit". Then I try to install MS VS2005 but didn't install all updates for MSWindowsXPsp2 and again didn't see the messageBox "OnDocumentComplete : about:blank", but see the messageBox "OnQuit". Finally I install all updates for MSWindowsXPsp2 from microsoft site and then MS VS2005 then I see the messageBox "OnDocumentComplete : about:blank" and "OnQuit". But if I install MS VS2005 and then all updates for MSWindowsXPsp2 then not woking (didn't see the messageBox "OnDocumentComplete : about:blank", but see the messageBox "OnQuit").

What's problem??? What specifically updates need for correct working in MSWindowsXPsp2???

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