WndProc(ref Message m) problem

Question

I have overriden the WndProc method for a burning application I've been working on. I do this to detect DEVICEARRIVAL and DEVICEREMOVECOMPLETE.

I have a Burner class. When this class object is initialized on the burner form, it initializes a backgroundworker. I also have a method inside the Burner class called 'Burn' that will eventually call _backgroundBurnerWorker.RunWorkerAsync()

So if you think about it in a linear fashion it would go like this:

Burn button clicked -> Burner.Burn - > BackgroundBurnerWorker.RunWorkerAsync() - > Back to the form thread here which calls the WndProc method. At this point it goes into a seemingly endless loop and never actually runs the DoWork method.

I've tried moving the base.WndProc to the top of the overriden method and it works when I run it in debug mode but not when I install it.

I would prefer to break out of the WndProc method so that the DoWork can actually burn a disc and report progress but I am unclear of how I should do this. Suggestions would be wonderful!

If there is an easier way to detect when media has been inserted or removed, please do share!

Sam Hobbs · Answer

Thank you for the sample code and thank you for making it simple. The problem with the BackgroundWorker is that you do not set the BackgroundWorker.DoWork member. So add the following to the Burner class constructor: _backgroundWorker.DoWork += new DoWorkEventHandler(BackgroundWorker_DoWork); The other problem is that the WM_DEVICECHANGE message is not documented well enough. So to understand it better try the following for your WndProc: protected override void WndProc( ref Message m) { string s; switch (m.Msg) { case WM_DEVICECHANGE: s = string .Format( Id 0x{0:X} data: 0x{1:X}\r\n  m.WParam m.LParam); textBox1.AppendText(s); break ; } base .WndProc( ref m); } Note that WM_DEVICECHANGE is: private const int WM_DEVICECHANGE = 0x0219;

Joel Reid · Answer

Thanks for pointing that out Sam! Totally missed the event handler. It works perfectly now! Thanks again! Joel

Sam Hobbs · Answer

Note that you do not have to use a switch statement since you are checking for only one message. You can convert that to a simple if statement if you wish. Also note that in my code textBox1 is a multiline TextBox. It is a better way to see what is happening

Joel Reid · Answer

I forgot to mention MessageBox.Show(Doing work) is never reached. I set my breakpoint where _backgroundWorker.RunWorkerAsync() is called and then step in from there. You'll see what i'm talking about.

Joel Reid · Answer

Ok so I tried throwing it in an if statement within a test application since I haven't been back to work. It still doesn't solve the problem. Here's the code from the test application: Burner.cs: using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; namespace WndProcTest { public class Burner { private BackgroundWorker _backgroundWorker; public Burner() { _backgroundWorker = new BackgroundWorker(); _backgroundWorker.WorkerSupportsCancellation = true; _backgroundWorker.WorkerReportsProgress = true; } public void Burn() { _backgroundWorker.RunWorkerAsync(); } public void BackgroundWorker_DoWork(object sender DoWorkEventArgs e) { MessageBox.Show(Doing work); } } } Form1.cs: using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; namespace WndProcTest { public partial class Form1 : Form { public Form1() { InitializeComponent(); } protected override void WndProc(ref Message m) { if (m.WParam.ToInt32() == 0x8000) { MessageBox.Show(something arrived); } base.WndProc(ref m); } private void Form1_Load(object sender EventArgs e) { } private void button1_Click(object sender EventArgs e) { Burner b = new Burner(); b.Burn(); } } }

Joel Reid · Answer

Ok I will try that suggestion when I go back to work after the Holidays. Thanks for the help both of you! I will let you know how it goes. Happy holidays!

Sam Hobbs · Answer

You should do as Kirtan suggests at least for the sake of efficiency except I suggest first checking the message id (Message.Msg Property) for WM_DEVICECHANGE (0x0219). Filter by message id first; perhaps using a switch statement. If there are many message ids then a message map is usually used but I assume that is not needed for your application.

Sam Hobbs · Answer

A very possible explanation is that your code is getting an undetected error. You might be surprised that it is possible. C# will silently stop executing a method when it gets an error that is ignored. That problem can be frustrating to diagnose. So possibly the DoWork is not being executed because of an error in your program. You can detect errors using try/catch.

Kirtan Patel · Answer

if you don't want to process that extra messages you are talking about place if condition to messages which contain only DeviceRemoval and DeviceArrival messages only. Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable{mso-style-name:Table Normal;mso-tstyle-rowband-size:0;mso-tstyle-colband-size:0;mso-style-noshow:yes;mso-style-priority:99;mso-style-parent:;mso-padding-alt:0in 5.4pt 0in 5.4pt;mso-para-margin-top:0in;mso-para-margin-right:0in;mso-para-margin-bottom:10.0pt;mso-para-margin-left:0in;line-height:115%;mso-pagination:widow-orphan;font-size:11.0pt;font-family:Calibrisans-serif;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:Times New Roman;mso-bidi-theme-font:minor-bidi;} protected override void WndProc ( ref Message m ) { if ( m . WParam . ToInt32 () == DeviceInserted ) { MessageBox . Show ( Device Inserted ! ); } else if ( m . WParam . ToInt32 () == DeviceRemoved ) { MessageBox . Show ( Device Removed ! ); } base . WndProc ( ref m ); }

Sam Hobbs · Answer

Note that you said  which calls the WndProc method . Please understand that I thought you were saying that you were calling the WndProc method . Note that people that answer questions do not like it when people ask the same question multiple times at the same time. That is because thy might waste their time answering a question that is answered elsewhere. Thank you for linking to the other thread. I am busy at the moment so I will look at this again later but hopefully you will get help in the other thread.

Joel Reid · Answer

I made another post on dreamincode as well that has the code for the Burn method and the wndproc method. I get the feeling that the problem isn't with my Burn method but more so with how the WndProc is handling these messages. Some of the messages I remember it catching was GET_TEXTLENGTH and WM_NQACTIVATE or similar. It would keep looping through roughly 5-6 different messages. http://www.dreamincode.net/forums/topic/260689-protected-override-void-wndprocref-message-m-goes-into-loop/

Joel Reid · Answer

I'm sorry I didn't miss anything you wrote I don't think you understand yet what my problem is and have jumped to assumptions. The WndProc override is not something you call. It is automatically called anytime windows sends a message to my form. So when I stick a CD in my CD Burner and close the tray Windows sends a message to my form saying hey there was an event that just happened let's take a look at it and determine if we need to do anything. If that event matches DBT_DEVICEARRIVAL then it runs a method I have to detect if it is a CD-R DVD+R HD etc. This also determines whether the currently selected recorder can support the detected media. As far as I can tell that is the only way to auto detect something being inserted into a removable drive. There's 2 files. My BurnerUI.cs and my Burner.cs (the class object.) My burn button does not call WndProc. What my Burn button does do is call a method in my Burner class called Burn (see my original post.) The Burn method tells my backgroundWorker to DoWork through the BackgroundWorker.RunWorkerAsync() call. However when I am debugging the code and the BackgroundWorker.RunWorkerAsync() is called (from the Burner.cs file) it switches back to the BurnerUI (BurnerUI.cs) thread to finish handling anything else in my Burn button click event (which there is nothing.) During that switch it sends messages back to my form that in turn gets stuck in a loop and does not switch back to the BackgroundWorker thread. I can step-out of that method when debugging to force it to burn but that does me no good. So I am only interested in 2 things right now. 1 is there a better way to auto-detect windows events and 2 if there is not a better way to auto-detect windows events is there a way to force a step-out of the WndProc method to stop accepting windows messages temporarily.

Sam Hobbs · Answer

You missed the most important part of what I said. Do not call WndProc in your Burn button clicked handler.

Joel Reid · Answer

Yes I do mean the DBT_DEVICEARRIVAL in the DEVICECHANGE message. In my form's code there is an override for the WndProc. It relates to my question because I have to detect when some type of removable media is inserted into the machine. So essentially it does it's part in that aspect. I can safely run my methods to detecting what type of media it is. CD-R DVD+R etc. My Burner class uses a background worker to do the burning. There is a Burn method that says BackgroundWorker.RunWorkerAsync (calls the do work part) However when it gets to that point in the code and calls RunWorkerAsync it switches back to the form code and sees that the form was sent a message instead of going straight to the DoWork method. So when it switches back to the form code and see's all these messages it somehow gets stuck in a loop and continuously sees the same messages to the form over and over and over and never goes to the DoWork method. The kicker is it only does this when the burner application is installed or set to release configuration in visual studio. But when it is in debug mode it steps out of the WndProc override and goes to the DoWork method. I'm not at work right now or I would post some code to help you understand.

Sam Hobbs · Answer

When you say DEVICEARRIVAL do you mean the DBT_DEVICEARRIVAL event in the WM_DEVICECHANGE message? You say you have overriden the WndProc method .... to detect DEVICEARRIVAL and DEVICEREMOVECOMPLETE. I do not understand however how that relates to the rest of the question. I think that you are saying that in your Burn button clicked handler you are calling the WndProc method. That is a likely problem; I doubt that you should do that. Since most of your question is describing what the program does in the Burn button clicked handler I do niot understand what you need to do when media has been inserted or removed.