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NAudio hanging and crashing when default device is changed

I've been stuck on this all day, so I'm going to post everything I've been able to find today that might be useful to helping me, it will be a long post. I'm having 2 issues that I believe are related to the same problem. First, let me explain what I am doing. I have 3 Winforms combo boxes that are bound to lists of all of the devices found by MMDeviceEnumerator. Two output device boxes, one input device. I am using the MMDeviceEnumerator to register a callback for whenever the devices are changed, removed, or a default device is set. The callback fires an event that then invokes a delegate to the form thread to re-enumerate the devices into combo boxes. It looks like this:
public void OnDefaultDeviceChanged(DataFlow dataFlow, Role deviceRole, string defaultDeviceId)
{
Devices.OnDevicesUpdated();
}
//The handler called by this event:
private void UpdateDeviceSelectors(object? sender = null, EventArgs? e = null)
{
Invoke(delegate ()
{
int primaryIndex = Devices.PrimaryOutput + 1, secondaryIndex = Devices.SecondaryOutput + 2, microphoneIndex = Devices.Microphone + 1;
Devices.Refresh();
try
{
SecondaryOutputComboBox.SelectedIndex = secondaryIndex;
PrimaryOutputComboBox.SelectedIndex = primaryIndex;
MicrophoneSelectComboBox.SelectedIndex = microphoneIndex;
}
catch (Exception ex)
{
Debug.WriteLine(ex.Message);
}
});
}
Now for the two issues I have. The first one involves a semi-random crash that leads back to NAudio.Wasapi.dll, where a System.ExecutionEngineException is thrown. It is kind of easy to reproduce. All I do is change the values of the combo boxes, switch the default devices around, and it will randomly crash.
The second issue occurs when another part of my code is involved. I have a microphone injector, which redirects a WaveInEvent that records a selected input device to a WaveOutEvent, like a loopback. Here is the relevant code for this:
public void Start()
{
if (Soundboard.Devices.SecondaryOutput == -2) return;
micStream = new WaveInEvent();
micStream.BufferMilliseconds = 50;
micStream.WaveFormat = new WaveFormat(44100, WaveIn.GetCapabilities(Soundboard.Devices.Microphone).Channels);
micStream.DeviceNumber = Soundboard.Devices.Microphone;
WaveInProvider waveIn = new(micStream);
var volumeSampleProvider = new VolumeSampleProvider(waveIn.ToSampleProvider());
volumeSampleProvider.Volume = 1 + Settings.Default.MicrophoneGain;
virtualCable = new WaveOutEvent();
virtualCable.DesiredLatency = 150;
virtualCable.DeviceNumber = Soundboard.Devices.SecondaryOutput;
virtualCable.Init(volumeSampleProvider);
micStream.StartRecording();
virtualCable.Play();
}
public void Stop()
{
try
{
if (micStream != null && virtualCable != null)
{
micStream.Dispose();
micStream = null;
virtualCable.Dispose();
virtualCable = null;
}
}
catch
{
micStream = null;
virtualCable = null;
}
}
In the delegate mentioned earlier, I am calling the Stop method of the Mic Injector and then the Start method to refresh the WaveIn and WaveOut devices to use the current device numbers so users do not see a device selected when a different device is being used. When this happens, the program, rather than crashing instantly and inconsistently, always hangs and has to be killed from the task manager. I am certain these 2 problems are related to the same root cause, but I have no idea what that root cause may be. Switching to Wasapi, DirectSound, or ASIO won't work because they lack certain functionalities I need, so I would really like to get this working still using Wave streams.
I've tried to find different ways to detect the device changes, assuming it is an issue deep inside NAudio, but I just can't find anything else. For the second problem specifically, I have moved the calls to the Mic Injector around thinking it may be a threading issue or something, but it didn't work or change the behavior.

MessageBox and while loop C#

I'm modifying existing C# code in order to pilote a piston. Every 30ms, I have a direct feedback of the position of this piston, through an event. The value is stored in a global variable I use to get the current position of the piston.
What I'm trying to achieve: for a given distance input (A->C), I want the piston to travel at full speed for 95% of the distance (A->B), and then slower for the remaining 5% (B->C).
I have access to a command that defines the speed and the destination of the piston : pos(velocity, destination).
However, if I write that code:
pos(fullSpeed,B);
pos(reducedSpeed, C);
the piston directly goes from fullSpeed to reducedSpeed
I tried to use a while loop to compare the current position of the piston with the goal destination, however, upon entering the while loop, the variable storing the piston position does not update anymore.
However, I noticed that by throwing a MessageBox in between, the position value keeps on getting updated, and I can simply click "ok" to launch the second command.
pos(fullSpeed,B);
MessageBox.show("Wait");
pos(reducedSpeed, C);
I would like to know why the "while" loop stops the update of the position variable but the MessageBox does not. I mean, as long as I don't click the "ok" button, the box is here preventing me from doing anything, which for me ressembles a while loop behaviour. Is there another way for me to do this instead of the MessageBox ?
I have little to no knowledge when it comes to C# and no support. I have tried to look in the documentation, but I did not find an answer (I have probably missed it). Any lead is more than welcome.
EDIT: I have no documentation for that code, and it is barely commented. Here is what I gathered (really hope it helps):
To move the piston, taht function is called:
MyEdc.Move.Pos(control, speed, destination, ref MyTan);
control simply define what we pilote (a distance or a load, it is an enum), and I have no idea what MyTan does. Only thing I know is that the MyEdc.Move.Pos returns an error code.
If I look at the definition of "pos", I am redirected to class
public DoPEmove Move;
containing among other things:
public DoPE.ERR Pos(DoPE.CTRL MoveCtrl, double Speed, double Destination, ref short Tan);
DoPE.ERR is also an type enum. However, I cannot reach the definition of a function named "Pos". Coud it be within the .dll included ?
The following is the code that allows me to access the position of the piston (without the global variables):
private int OnData(ref DoPE.OnData Data, object Parameter)
{
if (Data.DoPError == DoPE.ERR.NOERROR)
{
DoPE.Data Sample = Data.Data;
Int32 Time = Environment.TickCount;
if ((Time - LastTime) >= 300 /*ms*/)
{
LastTime = Time;
string text;
text = String.Format("{0}", Sample.Time.ToString("0.000"));
guiTime.Text = text;
text = String.Format("{0}", Sample.Sensor[(int)DoPE.SENSOR.SENSOR_S].ToString("0.000"));
guiPosition.Text = text;
text = String.Format("{0}", Sample.Sensor[(int)DoPE.SENSOR.SENSOR_F].ToString("0.000"));
guiLoad.Text = text;
text = String.Format("{0}", Sample.Sensor[(int)DoPE.SENSOR.SENSOR_E].ToString("0.000"));
guiExtension.Text = text;
}
}
return 0;
}
Which is called using
MyEdc.Eh.OnDataHdlr += new DoPE.OnDataHdlr(OnData);
I realise how little I know on how the soft operates, and how frustrating this is for you. If you think this is a lost cause, no problem, I'll try Timothy Jannace solution, and if it does not help me, I'll stick with the MessageBox solution. I just wanted to know why the MessageBox allowed me to sort of achieve my objectif, but the while loop did not, and how to use it in my advantage here.

I tried to use a while loop to compare the current position of the
piston with the goal destination, however, upon entering the while
loop, the variable storing the piston position does not update
anymore.
While you are in the while loop, your app can no longer receive and process the feedback event.
One possible solution would be to use async/await like this:
private const int fullSpeed = 1;
private const int reducedSpeed = 2;
private int currentPistonPositon = 0; // global var updated by event as you described
private async void button1_Click(object sender, EventArgs e)
{
int B = 50;
int C = 75;
pos(fullSpeed, B);
await Task.Run(() =>
{ // pick one below?
// assumes that "B" and "currentPistonPosition" can actually be EXACTLY the same value
while (currentPistonPositon != B)
{
System.Threading.Thread.Sleep(25);
}
// if this isn't the case, then perhaps when it reaches a certain threshold distance?
while (Math.Abs(currentPistonPositon - B) > 0.10)
{
System.Threading.Thread.Sleep(25);
}
});
pos(reducedSpeed, C);
}
Note the button1_Click method signature has been marked with async. The code will wait for the while loop inside the task to complete while still processing event messages because of the await. Only then will it move on to the second pos() call.
Thank you for your answer ! It works like a charm ! (good catch on the
EXACT value). I learnt a lot, and I am sure the async/await combo is
going to be very usefull in the future ! – MaximeS
If that worked well, then you might want to consider refactoring the code and making your own "goto position" method like this:
private void button1_Click(object sender, EventArgs e)
{
int B = 50;
int C = 75;
GotoPosition(fullSpeed, B);
GotoPosition(reducedSpeed, C);
}
private async void GotoPosition(int speed, int position)
{
pos(speed, position);
await Task.Run(() =>
{
while (Math.Abs(currentPistonPositon - position) > 0.10)
{
System.Threading.Thread.Sleep(25);
}
});
}
Readability would be greatly improved.
You could even get fancier and introduce a timeout concept into the while loop. Now your code could do something like below:
private void button1_Click(object sender, EventArgs e)
{
int B = 50;
int C = 75;
if (GotoPosition(fullSpeed, B, TimeSpan.FromMilliseconds(750)).Result)
{
if (GotoPosition(reducedSpeed, C, TimeSpan.FromMilliseconds(1500)).Result)
{
// ... we successfully went to B at fullSpeed, then to C at reducedSpeed ...
}
else
{
MessageBox.Show("Piston Timed Out");
}
}
else
{
MessageBox.Show("Piston Timed Out");
}
}
private async Task<bool> GotoPosition(int speed, int position, TimeSpan timeOut)
{
pos(speed, position); // call the async API
// wait for the position to be reached, or the timeout to occur
bool success = true; // assume we have succeeded until proven otherwise
DateTime dt = DateTime.Now.Add(timeOut); // set our timeout DateTime in the future
await Task.Run(() =>
{
System.Threading.Thread.Sleep(50); // give the piston a chance to update maybe once before checking?
while (Math.Abs(currentPistonPositon - position) > 0.10) // see if the piston has reached our target position
{
if (DateTime.Now > dt) // did we move past our timeout DateTime?
{
success = false;
break;
}
System.Threading.Thread.Sleep(25); // very small sleep to reduce CPU usage
}
});
return success;
}

If you're using events you are probably having concurrency issues. Especially with events being raised every 30ms!
A very simple way to handle concurrency is to use a lock object to prevent different threads from using contested resources simultaneously:
class MyEventHandler
{
private object _lockObject;
MyEventHandler()
{
_lockObject = new object();
}
public int MyContestedResource { get; }
public void HandleEvent( object sender, MyEvent event )
{
lock ( _lockObject )
{
// do stuff with event here
MyContestedResource++;
}
}
}
Keep in mind that is very simple and by no means perfect in every scenario. If you provide more information about how the events are raised and what you're doing with them people will be able to provide more help.
EDIT:
Using that signature you posted for the Pos method I was able to find documentation on the library you are using: https://www.academia.edu/24938060/Do_PE
The reason you only see the method signature when you goto definition is because the library has been compiled into a dll. Actually, it probably wouldn't be that useful to see the code anyway because it looks like the library is a C# wrapper around native (c or c++) code.
Anyways, I hope the documentation is helpful to you. If you look at page 20 there are some pointers on doing movement. This is going to be a challenge for a new programmer but you can do it. I would suggest you avoid using the event handler to drive your logic and instead stick with using the synchronous versions of commands. Using the synchronous commands your code should operate the same way it reads.

I believe what you'll want to do is add a call to:
Application.DoEvents();
This will allow your application to process posted messages (events), which will allow that global variable to be updated.
I just wanted to know why the MessageBox allowed me to sort of achieve my objectif, but the while loop did not, and how to use it in my advantage here.
The reason that works is because you're giving the WndProc a chance to process events which have been sent to the application. It's not an intended feature of that call to MessageBox.Show();, but it is a consequence. You can do the same thing with a call to Application.DoEvents(); without the interruption of the message box.

How can I prevent a DLL from causing problems when it is used more than once?

As Peter Duniho points out in a comment here, I was fixated on a red herring when I should have been focusing on something else altogether.
When I use Symbol.Barcode.Reader and Symbol.Barcode.ReaderData in one form, they work fine. I use them as I document here.
However, when I go from one form that uses the barcode scanning code to another one that also does, all Dallas breaks loose. I get the following exception in the second form, on startup:
Symbol.Exceptions.OperationFailureException: SCAN_GetInterfaceParams
at Symbol.Barcode.InterfaceParams.GetInterfaceParams()
at Symbol.Barcode.InterfaceParams..ctor(Reader reader)
at Symbol.Barcode.Actions.Enable()
at HHS.frmFind.InitReader()
at HHS.frmFind.textBoxScan_GotFocus(Object sender, EventArgs e)
at System.Windows.Forms.Control.OnGotFocus(EventArgs e)
at System.Windows.Forms.Control.WnProc(WM wm, Int32 wParam, Int32 lParam)
at System.Windows.Forms.Control._InternalWnProc(WM wm, Int32 wParam, Int32 lParam)
at Microsoft.AGL.Forms.WL.SetVis(IntPtr hwnThis, BOOL fVis)
at System.Windows.Forms.Control.set_Visible(Boolean value)
at System.Windows.Forms.Form.ShowDialog()
The barcode scanning code between the two forms is identical, so it's not the code itself (it works fine the first time, in the first form).
The exception occurs immediately in the second form when the textbox that is set up for scanning is entered. It's GotFocus() event fires because the textbox gets focus when the form is displayed; OnGotFocus() calls InitReader(), which then fails. InitReader() is:
private bool InitReader()
{
ExceptionLoggingService.Instance.WriteLog("Reached frmFind.InitReader");
// If reader is already present then retreat
if (this.barcodeReader != null)
{
return false;
}
// Create new reader, first available reader will be used.
this.barcodeReader = new Symbol.Barcode.Reader();
// Create reader data
this.barcodeReaderData = new Symbol.Barcode.ReaderData(
Symbol.Barcode.ReaderDataTypes.Text,
Symbol.Barcode.ReaderDataLengths.MaximumLabel);
// Create event handler delegate
this.barcodeEventHandler = this.BarcodeReader_ReadNotify;
// Enable reader, with wait cursor
this.barcodeReader.Actions.Enable();
this.barcodeReader.Parameters.Feedback.Success.BeepTime = 0;
this.barcodeReader.Parameters.Feedback.Success.WaveFile = "\\windows\\alarm3.wav";
// Attach to activate and deactivate events
this.Activated += ReaderForm_Activated;
this.Deactivate += ReaderForm_Deactivate;
return true;
}
The objects being dealt with there are in Symbol.Barcode.dll, from Motorola. They are declared in the form like so:
private Symbol.Barcode.Reader barcodeReader;
private Symbol.Barcode.ReaderData barcodeReaderData;
If I bypass the first form, which has the same type of barcode scannig code, and go straight to this form, it doesn't crash.
So apparently it's that the closely related bits of code can't coexist. Why not and, more importantly, how can I prevent this revolting development?
UPDATE
With this logging added to InitReader:
private bool InitReader()
{
ExceptionLoggingService.Instance.WriteLog("Reached frmFind.InitReader");
// If reader is already present then retreat
if (this.barcodeReader != null)
{
return false;
}
// Create new reader, first available reader will be used.
ExceptionLoggingService.Instance.WriteLog("Reached frmFind.InitReader #2");
this.barcodeReader = new Symbol.Barcode.Reader();
// Create reader data
ExceptionLoggingService.Instance.WriteLog("Reached frmFind.InitReader #3");
this.barcodeReaderData = new Symbol.Barcode.ReaderData(
Symbol.Barcode.ReaderDataTypes.Text,
Symbol.Barcode.ReaderDataLengths.MaximumLabel);
// Create event handler delegate
ExceptionLoggingService.Instance.WriteLog("Reached frmFind.InitReader #4");
this.barcodeEventHandler = this.BarcodeReader_ReadNotify;
// Enable reader, with wait cursor
ExceptionLoggingService.Instance.WriteLog("Reached frmFind.InitReader #5");
this.barcodeReader.Actions.Enable();
this.barcodeReader.Parameters.Feedback.Success.BeepTime = 0;
this.barcodeReader.Parameters.Feedback.Success.WaveFile = "\\windows\\alarm3.wav";
// Attach to activate and deactivate events
ExceptionLoggingService.Instance.WriteLog("Reached frmFind.InitReader #6");
this.Activated += ReaderForm_Activated;
this.Deactivate += ReaderForm_Deactivate;
ExceptionLoggingService.Instance.WriteLog("Reached frmFind.InitReader #7");
return true;
}
...I see this in the log file after opening the Find form and crashing the app (it hangs for about 20 seconds before disappearing):
Date: 3/19/2009 11:43:38 PM
Message: Reached frmFind.InitReader
Date: 3/19/2009 11:43:38 PM
Message: Reached frmFind.I
...so it's crashing almost instantaneously after this block of code:
if (this.barcodeReader != null)
{
return false;
}
...as it only gets through half of the next logging line before rudely interrupting itself.
UPDATE 2
Fejesjoco may still be right (in his comment below), but I submit this logging code as exhibit "A":
public void WriteLog(string message)
{
if (!HHSConsts.Logging) return;
StringBuilder formattedMessage = new StringBuilder();
formattedMessage.AppendLine("Date: " + DateTime.Now.ToString());
formattedMessage.AppendLine("Message: " + message);
_streamWriter.WriteLine(formattedMessage.ToString());
_streamWriter.Flush();
}
The stream should get flushed after each line is written to the log.
UPDATE 3
The failure is always very consistent as to how long it "hangs" before it crashes; I can see the cursor blinking in the bar code text box of the find form, and it pulsates about 20 times (I actually counted it last time: 24).
This also is a bit odd; in Update 2, I showed the contents of the log file with all the log entries sprinkled into the InitReader method. With those commented out (except for the first one), the log file ends with:
Date: 3/20/2009 12:01:22 AM
Message: Reached frmFind.InitReader
Date: 3/20/2009 12:01:22 AM
Message: From application-wide exception handler: Symbol.Exceptions.OperationFailureException: SCAN_GetInterfaceParams
at Symbol.Barcode.InterfaceParams.GetInterfaceParams()
at Symbol.Barcode.InterfaceParams..ctor(Reader reader)
at Symbol.Barcode.Actions.Enable()
at HHS.frmFind.InitReader()
...so the additional log file entries were preventing the exception msg from getting logged.
UPDATE 4
Actions.Enable?
I was unfamiliar with this, and when I added "Actions." I got a choice between Symbol.Barcode.Actions and Symbol.Generic.Actions.
I chose the first first, but it has no "Enable" method. Adding it scolded me with, "An object reference is required for the non-static field, method, or property 'Symbol.Generic.Actions.Enable()'"
I then commented out the using that was added, entered "Actions." again, and this time chose Symbol.Generic.Actions (and got the same err msg for my troubles).
How can I use Actions.Enable()?
UPDATE 5
C.Evenhuis: by "some events require re-attaching each time they occur" do you mean this:
private void StartRead()
{
// If we have both a reader and a reader data
if ((this.barcodeReader != null) && (this.barcodeReaderData != null))
{
// Submit a read
this.barcodeReader.ReadNotify += this.barcodeEventHandler;
this.barcodeReader.Actions.Read(this.barcodeReaderData);
}
}
private void StopRead()
{
// If we have a reader
if (this.barcodeReader != null)
{
// Flush (Cancel all pending reads)
this.barcodeReader.ReadNotify -= this.barcodeEventHandler;
this.barcodeReader.Actions.Flush();
}
}
...(barcodeReader.ReadNotify is attached in StartRead and detached in StopRead), or is more necessary?
I also have, in InitReader():
this.Activated += ReaderForm_Activated;
this.Deactivate += ReaderForm_Deactivate;
...which are implemented like so:
private void ReaderForm_Activated(object sender, EventArgs e)
{
// If there are no reads pending on barcodeReader start a new read
if (!this.barcodeReaderData.IsPending)
{
this.StartRead();
}
}
private void ReaderForm_Deactivate(object sender, EventArgs e)
{
this.StopRead();
}
InitReader() is called from textBoxScan_GotFocus(); textBoxScan has the focus when the form displays.
UPDATE 6
As to "Explicitly Close() classes before you Dispose() them", I call Dispose on two things, Symbol.Barcode.Reader and Symbol.Barcode.ReaderData, and neither one allows a Close() call.
UPDATE 7
This statement from C. Evenhuis: "you can't have two (foreground) readers enabled" led me to try the following:
private void FrmDelivery_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
this.barcodeReader.Actions.Disable();
}
...which seems to have pretty much done the trick - I can open the Find form without a hang resulting in an eventual crash. I can scan into the Find form after having scanned into the Delivery form. The only (unrelated?) problem that I still see is that my Find form is still partially obscured for some reason...

Symbol Motorola Zebra is building on a legacy C++ library with a legacy .NET wrapper. There are quite some pitfalls (some events require re-attaching each time they occur, some classes require explicit Close() before you Dispose() them, etc).
As you may have found out, you can invoke members of the Symbol classes from multiple threads / forms, but you can't have two (foreground) readers enabled, and some properties can only be set if no background readers are enabled, and there is no way to determine whether there are background readers enabled (ie DataWedge).
At our company we chose to initialize the scanner in the Form.Activated event and deinitialize it in the Deactivated event. Then when scanning was required, a call to Actions.Enable() would do the trick. Setting reader properties is done in try catch blocks :(
Quite odd that your application crashes at GetInterfaceParams, I would expect Setting them to cause trouble. Try your application with the bare minimum; don't set the BeepTime or WaveFile properties.

I'm not familiar with this type of scanner, but I can imagine initreader will do something at a hardware level. It will probably try to open some port. Because the port is already open it fails.
You need to implement a singleton service for your scanner instead of addressing it directly in your form. Then you can initialize the reader once for the complete application and use it wherever you'd like.
This will be a lot more 'SOLID' and thus more maintainable.

How to attach event to dynamic object or COM object

I think this article has the same problem with me. However, there's no workable solution for my case.
I'm using Windows Media Player ActiveX in my program.
For some reason, I don't want to add a reference of it and convert to AxHost automatically by IDE.
I create the instance by Activator and ProgID
protected const string WMP_PROG_ID = "WMPlayer.OCX.7";
private dynamic _wmp;
protected virtual bool init(){
try{
_wmp = Activator.CreateInstance(Type.GetTypeFromProgID(WMP_PROG_ID));
}
catch{ return false; }
return true;
}
I was tried to do this by Reflection, but I found that dynamic is suitable to my case.
Every property and method works alright, like these:
protected override bool setSpeed(float speed){
try{
_wmp.settings.rate = speed;
}
catch { return false; }
return true;
}
protected override int getLength(){
double res;
try{
res = _wmp.currentMedia.duration;
}
catch { return 0; }
return (int)(res * 1000);
}
Unfortunately, when I want to attach event like the article I indicated in the top, it got no work.
My code like this:
protected bool connectEvent(){
_wmp.StatusChange += new EventHandler(_wmp_StatusChange);
return true;
}
protected void _wmp_StatusChange(object sender, EventArgs e){
Console.WriteLine(_wmp.Status);
}
I've checked the type of event handler of StatusChange, it's EventHandler.
These codes compiled well, and I can load some music, play it, pause it, ...do anything I like.
But the StatusChange event never triggered.
I tried to set a break-point at connectEvent.
When run at _wmp.StatusChange += new EventHandler(...), the IntelliTrace give me some information.
Those information had written in Trad. Chinese, I think it means:
Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: Could not apply operator "+=" to type System.Dynamic.DynamicObject and System.EventHandler
Even though there's an exception, but just like I said, compile was passed, everything still work -- except I could not listen event.
So, how can I attach event successfully in the dynamic object _wmp?
Any possible solution (like Reflection) is useful to me.
Also, in the case above, the handler type of StatusChange is EventHandler.
But if I want to handle PlayStateChange event, it is an "Unknown handle" if I don't add a reference of wmp.dll.
I hope the solution is suitable to this case, too.
Thanks everyone in advance for all of your support, and please forgive me for my poor English.

The generic strategy to turn a program that uses a COM object from early bound to late bound calling is to first write it early bound. IntelliSense will help you fall in the pit of success, ensuring that you use correctly named methods, pass the right kind of arguments and particularly useful to help you find out what the event handler signatures should look like.
Which produces this bit of test code:
void testEarlyBound() {
var wmp = new WMPLib.WindowsMediaPlayer();
wmp.StatusChange += new WMPLib._WMPOCXEvents_StatusChangeEventHandler(wmp_StatusChange);
}
void wmp_StatusChange() {
throw new NotImplementedException();
}
With the StatusChange event handler assignment and method body completely auto-generated by IntelliSense. Note the signature of the event handler, it is not an EventHandler. Just a method that returns void and takes no arguments, it matches the Action delegate type. Now you have a good shot at writing the late-bound version without the undiagnosable runtime exceptions:
void testLateBound() {
dynamic wmp = Activator.CreateInstance(Type.GetTypeFromProgID("WMPlayer.OCX"));
wmp.StatusChange += new Action(wmp_StatusChange);
}

Blocking dialogs in .NET WebBrowser control

I have a .NET 2.0 WebBrowser control used to navigate some pages with no user interaction (don't ask...long story). Because of the user-less nature of this application, I have set the WebBrowser control's ScriptErrorsSuppressed property to true, which the documentation included with VS 2005 states will [...]"hide all its dialog boxes that originate from the underlying ActiveX control, not just script errors." The MSDN article doesn't mention this, however.
I have managed to cancel the NewWindow event, which prevents popups, so that's taken care of.
Anyone have any experience using one of these and successfully blocking all dialogs, script errors, etc?
EDIT
This isn't a standalone instance of IE, but an instance of a WebBrowser control living on a Windows Form application. Anyone have any experience with this control, or the underlying one, AxSHDocVW?
EDIT again
Sorry I forgot to mention this... I'm trying to block a JavaScript alert(), with just an OK button. Maybe I can cast into an IHTMLDocument2 object and access the scripts that way, I've used MSHTML a little bit, anyone know?

And for an easy way to inject that magic line of javascript, read how to inject javascript into webbrowser control.
Or just use this complete code:
private void InjectAlertBlocker() {
HtmlElement head = webBrowser1.Document.GetElementsByTagName("head")[0];
HtmlElement scriptEl = webBrowser1.Document.CreateElement("script");
string alertBlocker = "window.alert = function () { }";
scriptEl.SetAttribute("text", alertBlocker);
head.AppendChild(scriptEl);
}

This is most definitely hacky, but if you do any work with the WebBrowser control, you'll find yourself doing a lot of hacky stuff.
This is the easiest way that I know of to do this. You need to inject JavaScript to override the alert function... something along the lines of injecting this JavaScript function:
window.alert = function () { }
There are many ways to do this, but it is very possible to do. One possibility is to hook an implementation of the DWebBrowserEvents2 interface. Once this is done, you can then plug into the NavigateComplete, the DownloadComplete, or the DocumentComplete (or, as we do, some variation thereof) and then call an InjectJavaScript method that you've implemented that performs this overriding of the window.alert method.
Like I said, hacky, but it works :)
I can go into more details if I need to.

Bulletproof alert blocker:
Browser.Navigated +=
new WebBrowserNavigatedEventHandler(
(object sender, WebBrowserNavigatedEventArgs args) => {
Action<HtmlDocument> blockAlerts = (HtmlDocument d) => {
HtmlElement h = d.GetElementsByTagName("head")[0];
HtmlElement s = d.CreateElement("script");
IHTMLScriptElement e = (IHTMLScriptElement)s.DomElement;
e.text = "window.alert=function(){};";
h.AppendChild(s);
};
WebBrowser b = sender as WebBrowser;
blockAlerts(b.Document);
for (int i = 0; i < b.Document.Window.Frames.Count; i++)
try { blockAlerts(b.Document.Window.Frames[i].Document); }
catch (Exception) { };
}
);
This sample assumes you have Microsoft.mshtml reference added, "using mshtml;" in your namespaces and Browser is your WebBrowser instance.
Why is it bulletproof? First, it handles scripts inside frames. Then, it doesn't crash when a special "killer frame" exists in document. A "killer frame" is a frame which raises an exception on attempt to use it as HtmlWindow object. Any "foreach" used on Document.Window.Frames would cause an exception, so safer "for" loop must be used with try / catch block.
Maybe it's not the most readable piece of code, but it works with real life, ill-formed pages.

You may have to customize some things, take a look at IDocHostUIHandler, and then check out some of the other related interfaces. You can have a fair amount of control, even to the point of customizing dialog display/ui (I can't recall which interface does this). I'm pretty sure you can do what you want, but it does require mucking around in the internals of MSHTML and being able to implement the various COM interfaces.
Some other ideas:
http://msdn.microsoft.com/en-us/library/aa770041.aspx
IHostDialogHelper
IDocHostShowUI
These may be the things you're looking at implementing.

webBrowser1.ScriptErrorsSuppressed = true;
Just add that to your entry level function. After alot of research is when I came across this method, and touch wood till now its worked. Cheers!!

window.showModelessDialog and window.showModalDialog can be blocked by implementing INewWindowManager interface, additionally code below show how to block alert dialogs by implementing IDocHostShowUI
public class MyBrowser : WebBrowser
{
[PermissionSetAttribute(SecurityAction.LinkDemand, Name = "FullTrust")]
public MyBrowser()
{
}
protected override WebBrowserSiteBase CreateWebBrowserSiteBase()
{
var manager = new NewWindowManagerWebBrowserSite(this);
return manager;
}
protected class NewWindowManagerWebBrowserSite : WebBrowserSite, IServiceProvider, IDocHostShowUI
{
private readonly NewWindowManager _manager;
public NewWindowManagerWebBrowserSite(WebBrowser host)
: base(host)
{
_manager = new NewWindowManager();
}
public int ShowMessage(IntPtr hwnd, string lpstrText, string lpstrCaption, int dwType, string lpstrHelpFile, int dwHelpContext, out int lpResult)
{
lpResult = 0;
return Constants.S_OK; // S_OK Host displayed its UI. MSHTML does not display its message box.
}
// Only files of types .chm and .htm are supported as help files.
public int ShowHelp(IntPtr hwnd, string pszHelpFile, uint uCommand, uint dwData, POINT ptMouse, object pDispatchObjectHit)
{
return Constants.S_OK; // S_OK Host displayed its UI. MSHTML does not display its message box.
}
#region Implementation of IServiceProvider
public int QueryService(ref Guid guidService, ref Guid riid, out IntPtr ppvObject)
{
if ((guidService == Constants.IID_INewWindowManager && riid == Constants.IID_INewWindowManager))
{
ppvObject = Marshal.GetComInterfaceForObject(_manager, typeof(INewWindowManager));
if (ppvObject != IntPtr.Zero)
{
return Constants.S_OK;
}
}
ppvObject = IntPtr.Zero;
return Constants.E_NOINTERFACE;
}
#endregion
}
}
[ComVisible(true)]
[Guid("01AFBFE2-CA97-4F72-A0BF-E157038E4118")]
public class NewWindowManager : INewWindowManager
{
public int EvaluateNewWindow(string pszUrl, string pszName,
string pszUrlContext, string pszFeatures, bool fReplace, uint dwFlags, uint dwUserActionTime)
{
// use E_FAIL to be the same as CoInternetSetFeatureEnabled with FEATURE_WEBOC_POPUPMANAGEMENT
//int hr = MyBrowser.Constants.E_FAIL;
int hr = MyBrowser.Constants.S_FALSE; //Block
//int hr = MyBrowser.Constants.S_OK; //Allow all
return hr;
}
}

The InjectAlertBlocker is absolutely correct
code is
private void InjectAlertBlocker() {
HtmlElement head = webBrowser1.Document.GetElementsByTagName("head")[0];
HtmlElement scriptEl = webBrowser1.Document.CreateElement("script");
IHTMLScriptElement element = (IHTMLScriptElement)scriptEl.DomElement;
string alertBlocker = "window.alert = function () { }";
element.text = alertBlocker;
head.AppendChild(scriptEl);
}
References needed to be added is
Add a reference to MSHTML, which will probalby be called "Microsoft HTML Object Library" under COM references.
Add using mshtml; to your namespaces.
Get a reference to your script element's IHTMLElement:
Then you can use the Navigated event of webbrowser as:
private void InjectAlertBlocker()
{
HtmlElement head = webBrowser1.Document.GetElementsByTagName("head")[0];
HtmlElement scriptEl = webBrowser1.Document.CreateElement("script");
IHTMLScriptElement element = (IHTMLScriptElement)scriptEl.DomElement;
string alertBlocker = "window.alert = function () { }";
element.text = alertBlocker;
head.AppendChild(scriptEl);
}
private void webDest_Navigated(object sender, WebBrowserNavigatedEventArgs e)
{
InjectAlertBlocker();
}

Are you trying to implement a web robot? I have little experience in using the hosted IE control but I did completed a few Win32 projects tried to use the IE control. Disabling the popups should be done via the event handlers of the control as you already did, but I found that you also need to change the 'Disable script debugging xxxx' in the IE options (or you could modify the registry in your codes) as cjheath already pointed out. However I also found that extra steps needed to be done on checking the navigating url for any downloadable contents to prevent those open/save dialogs. But I do not know how to deal with streaming files since I cannot skip them by looking at the urls alone and in the end I turned to the Indy library saving me all the troubles in dealing with IE. Finally, I remember Microsoft did mention something online that IE is not designed to be used as an OLE control. According to my own experience, every time the control navigates to a new page did introduce memory leaks for the programs!

I had bigger problems with this: loading a webpage that is meant for printing and it displays annoying Print dialog. The InjectBlocker was the only way that worked, but fairly unreliable. Under certain conditions (I am considering it's due that WebBrowser control uses IE engine and this depends on installed IE version) the print dialog still appears. This is a major problem, the solution works on Win7 with IE9 installed, but WinXP with IE8 displays the dialog, no matter what.
I believe the solution is in modifying source code and removing the print javascript, before control renders the page. However I tried that with: DocumentText property of the webbrowser control and it is not working. The property is not read only, but it has no effect, when I modify the source.
The solution I found for my problem is the Exec script:
string alertBlocker = "window.print = function emptyMethod() { }; window.alert = function emptyMethod() { }; window.open = function emptyMethod() { };";
this.Document.InvokeScript("execScript", new Object[] { alertBlocker, "JavaScript" });

I managed to inject the code above by creating an extended WebBroswer class and overriding the OnNavigated method.
This seemed to work quite well:
class WebBrowserEx : WebBrowser
{
public WebBrowserEx ()
{
}
protected override void OnNavigated( WebBrowserNavigatedEventArgs e )
{
HtmlElement he = this.Document.GetElementsByTagName( "head" )[0];
HtmlElement se = this.Document.CreateElement( "script" );
mshtml.IHTMLScriptElement element = (mshtml.IHTMLScriptElement)se.DomElement;
string alertBlocker = "window.alert = function () { }";
element.text = alertBlocker;
he.AppendChild( se );
base.OnNavigated( e );
}
}

Simply from the browser control properties: scriptErrorSupressed=true

The easiest way to do this is :
In the : Webbrowser Control you have the procedure ( standard ) BeforeScriptExecute
( The parameter for BeforeScriptExecute is pdispwindow )
Add this :
pdispwindow.execscript("window.alert = function () { }")
In this way before any script execution on the page window alert will be suppressed by injected code.