We Keep Coding

Make my COM assembly call asynchronous

I've just "earned" the privilege to maintain a legacy library coded in C# at my current work.
This dll:
Exposes methods for a big legacy system made with Uniface, that has no choice but calling COM objects.
Serves as a link between this legacy system, and another system's API.
Uses WinForm for its UI in some cases.
More visually, as I understand the components :
*[Big legacy system in Uniface]* ==[COM]==> [C# Library] ==[Managed API]==> *[Big EDM Management System]*
The question is: One of the methods in this C# Library takes too long to run and I "should" make it asynchronous!
I'm used to C#, but not to COM at all. I've already done concurrent programming, but COM seems to add a lot of complexity to it and all my trials so far end in either:
A crash with no error message at all
My Dll only partially working (displaying only part of its UI, and then closing), and still not giving me any error at all
I'm out of ideas and resources about how to handle threads within a COM dll, and I would appreciate any hint or help.
So far, the biggest part of the code I've changed to make my method asynchronous :
// my public method called by the external system
public int ComparedSearch(string application, out string errMsg) {
errMsg = "";
try {
Action<string> asyncOp = AsyncComparedSearch;
asyncOp.BeginInvoke(application, null, null);
} catch (ex) {
// ...
}
return 0;
}
private int AsyncComparedSearch(string application) {
// my actual method doing the work, that was the called method before
}
Any hint or useful resource would be appreciated.
Thank you.
UPDATE 1:
Following answers and clues below (especially about the SynchronizationContext, and with the help of this example) I was able to refactor my code and making it to work, but only when called from another Window application in C#, and not through COM.
The legacy system encounters a quite obscure error when I call the function and doesn't give any details about the crash.
UPDATE 2:
Latest updates in my trials: I managed to make the multithreading work when the calls are made from a test project, and not from the Uniface system.
After multiple trials, we tend to think that our legacy system doesn't support well multithreading in its current config. But that's not the point of the question any more :)
Here is a exerpt of the code that seems to work:
string application;
SynchronizationContext context;
// my public method called by the external system
public int ComparedSearch(string application, out string errMsg) {
this.application = application;
context = WindowsFormsSynchronizationContext.Current;
Thread t = new Thread(new ThreadStart(AsyncComparedSearchAndShowDocs));
t.Start();
errMsg = "";
return 0;
}
private void AsyncComparedSearch() {
// ANY WORK THAT AS NOTHING TO DO WITH UI
context.Send(new SendOrPostCallback(
delegate(object state)
{
// METHODS THAT MANAGE UI SOMEHOW
}
), null);
}
We are now considering other solutions than modifying this COM assembly, like encapsulating this library in a Windows Service and creating an interface between the system and the service. It should be more sustainable..

It is hard to tell without knowing more details, but there are few issues here.
You execute the delegate on another thread via BeginInvoke but you don't wait for it. Your try\catch block won't catch anything as it has already passed while the remote call is still being executed. Instead, you should put try\catch block inside AsyncComparedSearch.
As you don't wait for the end of the execution of remote method (EndInvoke or via callback) I am not sure how do you handle the results of the COM call. I guess then that you update the GUI from within AsyncComparedSearch. If so, it is wrong, as it is running on another thread and you should never update GUI from anywhere but the GUI thread - it will most likely result with a crash or other unexpected behavior. Therefore, you need to sync the GUI update work to GUI thread. In WinForms you need to use Control.BeginInvoke (don't confuse it with Delegate.BeginInvoke) or some other way (e.g. SynchronizationContext) to sync the code to GUI thread. I use something similar to this:
private delegate void ExecuteActionHandler(Action action);
public static void ExecuteOnUiThread(this Form form, Action action)
{
if (form.InvokeRequired) { // we are not on UI thread
// Invoke or BeginInvoke, depending on what you need
form.Invoke(new ExecuteActionHandler(ExecuteOnUiThread), action);
}
else { // we are on UI thread so just execute the action
action();
}
}
then I call it like this from any thread:
theForm.ExecuteOnUiThread( () => theForm.SomeMethodWhichUpdatesControls() );
Besides, read this answer for some caveats.

C# Invoke Failing on Thread Function

I'm using a timer to regularly read-in a log file and post certain contents to a textbox in a Windows Form Application I'm developing in C#. I do this by sending a string to set_textbox_thread which posts the text (s) to the appropriate textbox (tbc) in the else below. The code below works in the practice application I built. However, the same code runs, but fails to update my textbox in the full application I'm building. It seems to be failing on the Invoke statement, which fails to call set_textbox_thread again. My theory is that, because my full application has a more complex set of controls, I am not calling Invoke via the correct control. I've tried calling it via "this" the parent panel, the parent form, and the button that triggers set_textbox_thread, and am dealing with the same outcome. Two questions:
Which control should I call Invoke under?
Is there a way to retrieve "the thread that owns the controls underlying windows handle? Can I do this through the Controls.Owner method?
I have tried making this Invoke call using try/catch, but am unable to retrieve an error message in the catch. Any ideas how to resolve the issue this way?
Thanks in advance!
private delegate void stringDelegate(string s);
private void set_textbox_thread(string s)
{
TextBox tbc = get_thread_tb();
if (tbc.InvokeRequired)
{
MessageBox.Show("Invoke Required");
stringDelegate sd = new stringDelegate(set_textbox_thread);
**this.Invoke(sd, new object[] {s });**
MessageBox.Show("Invoke Completed");
}
else
{

1) It doesn't matter what control you invoke under; there is only one UI thread and any control to marshal the call back to that UI thread.
2) what could you possibly do with this thread?
3) not much detail there. How do you know you have error messages? And what do you mean by "error messages"

Call invoke on the text box instead:
tbc.Invoke(sd, new object[] {s });

C# Forms: How to show a form when initalization takes a long time?

I have a c# form, and the initialization time takes a while (its getting information from a server, and populating a TreeView). Right now, the code looks similar to this:
public class myForm : Form
{
InitializeComponent();
List<Location> locations = getServerLocations(); // Server call
foreach( Location loc in locations )
{
List<POI> POIs = loc.getLocationPOIs(); // Server call
foreach( POI poi in POIs )
{
List<POIDetails> = poi.getPOIDetails(); // Server call
....
}
}
}
you get the point I think ... So there is a large tree, and I know I can not make the calls all the way down until the user expands the tree. But the intent is I just want the Form to display, with a 'loading...' or something on a tool strip while all the processing and server gets are happening.
Right now, it seems as if I haven't loaded the application yet because nothing will show to the user until all the calls are complete.

You shouldn't do any long running processing on the UI thread - instead move this to another thread i.e using a BackgroundWorker. You can initially show the "Loading" screen and, once the background worker completes, update your UI with your tree structure.

You should work with multi threading process, so that you can separate the process that takes time from the rest of the process. Here is a blog that may help you. .NET 4.0 and System.Threading.Tasks

Running your initialization on a separate thread is the preferred way. But if you're constrained to run it on the UI thread then try calling Application.DoEvents() right after your call to .Show() or .ShowDialog() of your form.
If the form shows up, it will still be unresponsive to user actions until the initialization is completed. So running the initialization on a separate thread is the better solution.

How to launch a Windows Form from within a .dll launched at runtime

I have researched this a fair bit and cannot establish the correct approach. My problem is as follows: I have a winForms applications and from within it I wish to launch a time intesive .dll. I can do this using System.Reflection no problem like this
// Execute the method from the requested .dll using reflection (System.Reflection).
//[System.Runtime.InteropServices.DllImport(strDllPath)]
DLL = Assembly.LoadFrom(strDllPath);
classType = DLL.GetType(String.Format("{0}.{0}", ListUfCmdParams[1]));
classInst = Activator.CreateInstance(classType);
XmlExpInfo = classType.GetMethod(DllParams[0]);
XmlExpInfo.Invoke(classInst, paramObj);
// Return something.
return String.Format("Method '{0}' from '{1}{2}' successfully executed!",
ListUfCmdParams[2], ListUfCmdParams[1], strDotDll);
this works great but the process being called is so time intensive I want to display to the user what is happening. To do this I have included in the .dll file a WinForm which has a progressBar and some other attributes. When I do this I get an exception. This occurs when "Activator.CreateInstance()" attempts to do its work: MissingMethodException "Cannot create an abstract class". I have come across this error before when I using partial classes and I had to remove the "partial" keyword from my classes to enable the .dll to execute correctly (which I just about got away with!). I cannot remove this "partial" keyword from the above winForms class so, the question is "How do I call a winForm from within my .dll (if indeed it is possible)?" so that the .dll can show its progress as it executes from the calling application?
Thanks for your time,
Nick
Ps. I have read the following threads and they are somewhat ambiguous:
A DLL with WinForms that can be launched from A main app
et al.

You should not make a callee (the dll) aware of it's caller (the form). Instead you could enrich the class in your dll that performs the time intensive method with a ProgressUpdated event:
public event ProgressUpdatedHandler ProgressUpdated;
public delegate void ProgressUpdatedHandler(object sender, int stepsCompleted, int stepsTotal)
This way the form could simply assign a handler for that event, and the dll could raise the event whenever it can indicate what the progress is.

I have just seen this question again and thought I would update as to how I eventually did this.
In the end I found the following to be the most effective way of performing the above for what I wanted. First you launch a WinForm which holds your progress information. Second youu envoke your "worker" method from within the "Shown" event.
The code for the first part i.e. to call the WinForm using Reflection is provided below:
// Execute the method from the requested .dll using reflection (System.Reflection).
Assembly DLL = Assembly.LoadFrom(strDllPath);
Type classType = DLL.GetType(String.Format("{0}.{0}", strNsCn));
object classInst = Activator.CreateInstance(classType, paramObj);
Form dllWinForm = (Form)classInst;
dllWinForm.ShowDialog();
I hope this helps someone else.

How to reload data in UITableView in MonoTouch?

In my application I display data from a online web service into several UITableViews. I have added several ways for the user to update the data, but the TableView.ReloadData() method does not seem to work.
When the user calls for an update, I get a new set of data from the server, pass it to the UITableViewSource instance that is attached to the UITableViewController and then call the ReloadData() method, which unfortunately does not in fact reload the data. Only after I return to the main screen and then go back to the table view (because it is already created, I just display the instance that already exists) does the new data show up in the tableview.
What am I doing wrong? I tried creating a new instance of the UITableViewSource when updating the data, but that does not help either.
Here is the code for loading data into the tableview (I reuse it for any event that requires data to be loaded into it):
dataControl.GetList(Tables.UPDATES)); //gets data from the server and passes it to the SQL database
Source source = GetSource(theType.Name, theType, groups); //creates a new source loaded with the data
Updates.TableView.Source = source;
Updates.TableView.AllowsSelection = false;
Updates.TableView.ReloadData();
This code is of course executed in a separate thread that invokes on the main thread.
Basically the same code is called when the user asks for an update(an animation is played while the background thread works).

Pavel is correct - try the following to see if it works:
InvokeOnMainThread(delegate{
Updates.TableView.Source = source;
Updates.TableView.AllowsSelection = false;
Updates.TableView.ReloadData();
});
In future, whenever you're dealing with something that will change the UI currently shown, you will need to ensure that it takes place on the main thread (also known as the GUI thread). This InvokeOnMainThread is a method from NSObject so can be called like above in all UIViews / UIViewControllers etc - you can also call it from an entirely C# class using:
MonoTouch.UIKit.UIApplication.SharedApplication.InvokeOnMainThread(delegate{ /*code here*/ });

You say it is done in a different thread, could it be that the worker thread cannot call the UI thread? I.e. you should call the ReloadData via delegate to be sure it gets called in the UI thread and not "only" in the worker thread, as it might interlock and never get actually called (happened to me in a different scenario).

I also ran into this problem and found this question. Using some of the hint here, I finally got it work by reseting the DataSource and call ReloadView().
tableView.DataSource = new MyDataSource(...);
tableView.RelaodData();
From my testing, it doesn't make different if I wrap the ReloadView() within the InvokeOnMainThread or not. Well, that's maybe because I'm not using worker thread.
It is strange that in another case I could refresh the table view by simply calling ReloadData() in ViewDidAppear(). The only difference is that the above case is the refresh within the same view.

You can reload datain viewwillappear() or set load data code in viewwillappear().

For googlers:
I had the same issues. This is what fixed it for me
InvokeOnMainThread(delegate {
myTableView.Source = new TableViewSource();
myTableView.ReloadData();
this.View.SetNeedsDisplay();
});