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C# Is action.BeginInvoke(action.EndInvoke,null) a good idea?

If I want to do a "fire and forget" of some code, but still want to ensure that my memory is cleaned up (per Why does asynchronous delegate method require calling EndInvoke?), will the following achieve that goal?
Action myAction = () => LongRunTime();
myAction.BeginInvoke(myAction.EndInvoke,null);
I've looked around but haven't seen that pattern used anywhere. Rather, people use an annonomoyus method as their callback (such as The proper way to end a BeginInvoke?) or they define an actual callback method. Since I haven't seen anyone else do this, it makes me think it either doesn't work or is otherwise a bad idea.
Thanks!

Using a method group conversion instead of a delegate is fine, the EndInvoke will still be called in on your Action. There is nothing else to be done, since this is a fire and forget call.
Unfortunately, it's somewhat hard to directly irrefutably prove that EndInvoke is called, since Action is a delegate and we can't just add a breakpoint on some class in the BCL.
This code will (periodically) inspect some private field of the IAsyncResult that is returned by BeginInvoke, which seems to keep track of whether or not EndInvoke has been called yet:
public partial class MainWindow : Window
{
private Timer _timer = new Timer(TimerCallback, null, 100, 100);
private static IAsyncResult _asyncResult;
public MainWindow()
{
InitializeComponent();
}
static void LongRunTime()
{
Thread.Sleep(1000);
}
void Window_Loaded(object sender, RoutedEventArgs args)
{
Action myAction = () => LongRunTime();
_asyncResult = myAction.BeginInvoke(myAction.EndInvoke, null);
}
static void TimerCallback(object obj)
{
if (_asyncResult != null)
{
bool called = ((dynamic)_asyncResult).EndInvokeCalled;
if (called)
{
// Will hit this breakpoint after LongRuntime has completed
Debugger.Break();
_asyncResult = null;
}
}
}
}
I've double checked using SOS that there aren't any managed memory leaks. I've also tried several other proofs, but they were more circumstantial than this one, I think.
Some interesting I discovered during my investigation: the myAction.BeginInvoke call will show up on profilers using instrumentation, but myAction.EndInvoke does not.

Nowdays it could be done like
BeginInvoke((Action)(async () =>
{
// Show child form
var f = new MyForm();
f.ShowDialog();
// Update parent/current
await UpdateData();
}));

Using MethodInvoker without Invoke

I am writing GUI applications for some time now and one thing I always use are MethodInvoker + lambda functions to do cross-thread access.
From the examples I find I always see stuff like this:
Version 1
if (InvokeRequired)
{
Invoke(new MethodInvoker(() =>
{
Label1.Text = "Foobar";
});
}
else
{
Label1.Text = "Foobar";
}
However this leads to code-duplication --> major baddie to me.
So what's wrong with this?
Version 2
MethodInvoker updateText = new MethodInvoker(() =>
{
Label1.Text = "Foobar";
});
if (InvokeRequired)
{
Invoke(updateText);
}
else
{
updateText();
}
Now I have the functionality bundled in one variable and call it with Invoke or as a function pointer when appropriate. Is version 2 worse performance-wise? Or is i bad practice to use anonymous functions for this?

Nothing's wrong with it... but you can add an extension method to make it all somewhat nicer:
public static void InvokeIfNecessary(this Control control,
MethodInvoker action)
{
if (control.InvokeRequired)
{
control.Invoke(action);
}
else
{
action();
}
}
Then you can write:
this.InvokeIfNecessary(() => Label1.Text = "Foobar");
Much neater :)
There is a very slight performance drawback from creating a delegate when you don't need to, but it's almost certainly insignificant - concentrate on writing clean code.
Note that even if you don't want to do that, you can still make your variable declaration simpler in your existing code:
MethodInvoker updateText = () => Label1.Text = "Foobar";
That's one benefit of using a separate variable - you don't need the new MethodInvoker bit to tell the lambda expression what type of delegate you want...

Is version 2 worse performance-wise? Or is i bad practice to use anonymous functions for this?
No version 2 is better, don't worry about performance problems with it. Instead of using an anonymous function you could also define a method:
public void SetLabelTextToFooBar()
{
Label1.Text = "Foobar";
}
and then:
if (InvokeRequired)
{
Invoke(SetLabelTextToFooBar);
}
else
{
SetLabelTextToFooBar();
}
or simply use a BackgroundWorker which will automatically execute all callbacks (such as RunWorkerCompleted and ProgressChanged) on the main UI thread so that you don't need to check for InvokeRequired.

Another practice on doing it:
Invoke((MethodInvoker)delegate
{
Label1.Text = "Foobar";
});

Multi threading delegate issue, Method name expected?

Right, this is my first venture into multi threading so could be something incredibly simple I'm missing but here goes...
I'm using thread pool to kick off a bunch of short running processes at the same time, each will be passed a URL to process/scrape for fb-tweets-google-plusones and return a result to my ReportProgress method by invoking the delegate ThreadDone but when passing in the processed object once the thread's done processing, i keep getting the error Method name expected but I'm passing in the method ReportProgress? I'm willing to bet (hoping) it's something incredibly simple that someone more experienced can spot right away. Here is what i have so far:
Delegate definition:
public delegate void ThreadDone(object sender, ScrapeResult scrapedResult);
DoWork:
public void DoWork(object sender)
{
while (true)
{
//lock the thread to prevent other threads from processing same job
lock (_threadLock)
{
string url = (string)sender;
result.URL = url;
if (chkFb.Checked)
{
result.Shares = grabber.GetFacebookShares(url);
}
if (chkTwitt.Checked)
{
result.Tweets = grabber.GetTweetCount(url);
}
if (chkPlusOne.Checked)
{
result.PlusOnes = grabber.GetPlusOnes(url);
}
this.Invoke(new ThreadDone(ReportProgress(sender, result))); //ERROR is on this line
}
Thread.Sleep(100);
}
}
ReportProgress:
private void ReportProgress(object sender, ScrapeResult scrapedResult)//<-- might not need?
{
progressBar.Value++;
ScrapeResult result = (ScrapeResult)sender;//ScrapedResult result = scrapedResult;
outputGrid.Rows.Add(result.URL, result.Shares, result.Tweets, result.PlusOnes);
outputGrid.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill;
outputGrid.AutoResizeColumns(DataGridViewAutoSizeColumnsMode.DisplayedCells);
}
Any help is greatly appreciated!

Change this:
this.Invoke(new ThreadDone(ReportProgress(sender, result)));
To:
this.Invoke(new ThreadDone(ReportProgress), sender, result);
The first parameter of Invoke() is the delegate, to build a delegate you do not need to give its parameters but only the method to call (that's why compiler says "method name expected") With new ThreadDone(ReportProgress) you create the new delegate and with 2nd and 3rd parameter of Invoke() you specify the parameters that will be passed to your delegate.

I would seriously consider using the TPL. Much cleaner to handle the finish of a task.

Can a method be attached to a delegate with predefined parameters?

Sometimes I encounter cases where I have to attach a method to a delegate but the signature doesn't match, like trying to attach abc down there to somedelegate with the string parameter being "hi".
public class test
{
//...
public void abc(int i, string x)
{
//Do Something
}
//...
}
public class test2
{
somedelegate x;
//...
public test2()
{
//Do Something
test y = new test();
x += y.abc(,"hi");
}
delegate void somedelegate(int i);
}
I can work it around by creating another delegate with the correct signature then attaching it but it seems so unnecessarily complex. Can you do something like this in C#? Thanks.
EDIT: I guess there closest to what I wanted to achieve is:
x += (int i) => abc(i, "hi");

Yes, you can do this with closures
[there's a nice treatment of the subject on msdn, but like anything else in there it's hard to find]
The Big Picture
Write a method that can take all the parameters you need
Inside that method you return an anonymous method with the delegate-target signature it requires
This method's call is itself the parameter in the delegate instantiation
Yes, this is a bit Matrix-y. But way cool.
delegate void somedelegate (int i);
protected somedelegate DelegateSignatureAdapter ( string b, bool yesOrNo, ...) {
// the parameters are local to this method, so we'll go w/ that.
// our target delegate requires a single int parameter and void return
return (int a) => {
// your custom code here
// all calling arguements are in scope - use them as needed
}; // don't forget the semicolon!
}
// our delegate call
somedelegate myWarpedDelegate = new somedelegate (DelegateSignatureAdapter("someString", true));
myWarpedDelegate (2543);
myWarpedDelegate(15);

Just Googling for '.net delegate optional parameters' returns some results that may be useful:
Can a Delegate have an optional parameter?
VB.NET - Is there a way to utilize optional parameters in delegates? (Or Plans to Allow this?)
Optional Parameters and Delegates
Update (researching this some more, and helped by the first link above):
Could you perhaps use the Invoke method, which accepts any delegate?

How to prevent duplicates, macro or something?

Well, the problem is that I've got a lot of code like this for each event passed to the GUI, how can I shortify this? Macros wont do the work I guess. Is there a more generic way to do something like a 'template' ?
private delegate void DownloadProgressDelegate(object sender, DownloaderProgressArgs e);
void DownloadProgress(object sender, DownloaderProgressArgs e) {
if (this.InvokeRequired) {
this.BeginInvoke(new DownloadProgressDelegate(DownloadProgress), new object[] { sender, e });
return;
}
label2.Text = d.speedOutput.ToString();
}
EDIT:
OK, how can I make this using anonymous delegate in BeginInvoke:
this.BeginInvoke(new DownloadProgressDelegate(DownloadProgress), new object[] { sender, e });

I personally prefer to put the actual action in an Action, then check if this requires an invoke -- this also has the benefit of not needing to declare so many delegates for use with your BeginInvokes. In other words,
void DownloadProgress(object sender, DownloaderProgressArgs e)
{
Action updateLabel = () => label2.Text = d.speedOutput.ToString();
if (this.InvokeRequired)
{
this.BeginInvoke(updateLabel);
}
else
{
updateLabel();
}
}
void DownloadSpeed(object sender, DownloaderProgressArgs e) {
Action updateSpeed = () =>
{
string speed = "";
speed = (e.DownloadSpeed / 1024).ToString() + "kb/s";
label3.Text = speed;
};
if (this.InvokeRequired)
{
this.BeginInvoke(updateSpeed);
}
else
{
updateSpeed();
}
}
This approach lends itself well to use an extension method on Controls that takes an Action and runs it through the check for InvokeRequired.
At a minimum, the extension method should look something like:
public static void MaybeInvoke(this Control c, Action action)
{
if (c.InvokeRequired)
{
this.BeginInvoke(action);
}
else
{
action();
}
}
Annoyingly, the non-generic Action wasn't introduced until .NET 3.5, so you would need to modify things a bit in the examples I gave -- probably using MethodInvoker -- if you're using an earlier version.

You could try T4... but I don't know if it will fit your case well.

One humble thought is to create one routine that handles all your BeginInvoke cases based on a request-type enumerate and using a switch statement. Then at least you only have to check InvokeRequired once. Note that you should probably use if/else rather than return to control the flow.

Well, one way could be to put the generic codes in static class, and access it like, for instance:
Utility.DownloadSpeedUpdate(frm, sender, e);

.net has (in one sense) a rather poor UI framework that actively encourages the problem you have, and the mixing of business logic and UI.
You may be able to make some headway with generics, delegates, and base class/static helper methods.
However, ideally, you need to layer a UI manager on top of .net that helps you out with this properly. This would allow you to separate the UI from the commands that it executes (i.e. you would dynamically bind UI events like keypresses, menu choices, button clicks etc to underlying command objects rather than handling the UI events directly). The UI event handlers would simply look up the command that is bound to the event, then call a centralised "execute Command X" method, and this would handle all the marshalling to the UI thread, etc.
As well as cleaning up this whole mess, this allows you to easily add things like key bindings and scripting/automation to your app, and makes the UI infinitely more scalable and maintainable.
It's no coincidence that this is the core command dispatch approach used in WCF - If you're not using WCF then it's unfortunately up to you to implement an equivalent. It takes a little bit of work to implement a basic command dispatch system, but unless your application is trivial, you'll be glad you did it.

Here's a sample that will save you a bunch of coding if you have many functions requiring InvokeRequired checks. You should notice a few important things:
I use EventHandler<DownloaderProgressArgs> instead of creating new delegates for each function.
The GetInvokeRequiredDelegate function wraps the code that is the same for all of these functions.
This code could be moved into a static class to let you share this among several forms, but that would require more work and a different structure. As it is here, the function just knows which form you're dealing with because the function exists inside that form.
This is all the code that I set up to test GetInvokeRequiredDelegate<T>():
public partial class Form1 : Form
{
public event EventHandler<DownloaderProgressArgs> OnDownloadProgress;
public event EventHandler<DownloaderProgressArgs> OnDownloadSpeed;
public Form1()
{
InitializeComponent();
OnDownloadProgress += GetInvokeRequiredDelegate<DownloaderProgressArgs>(DownloadProgress);
OnDownloadSpeed += GetInvokeRequiredDelegate<DownloaderProgressArgs>(DownloadSpeed);
new System.Threading.Thread(Test).Start();
}
public void Test()
{
OnDownloadProgress(this, new DownloaderProgressArgs() { DownloadSpeed = 1000, speedOutput = 5 });
OnDownloadSpeed(this, new DownloaderProgressArgs() { DownloadSpeed = 2000, speedOutput = 10 });
}
EventHandler<T> GetInvokeRequiredDelegate<T>(Action<object, T> action) where T : EventArgs
{
return ((o, e) =>
{
if (this.InvokeRequired)
{
this.BeginInvoke(action, new object[] { o, e});
} else
{
action(o, e);
}
});
}
void DownloadProgress(object sender, DownloaderProgressArgs d)
{
label2.Text = d.speedOutput.ToString();
}
void DownloadSpeed(object sender, DownloaderProgressArgs e)
{
string speed = "";
speed = (e.DownloadSpeed / 1024).ToString() + "kb/s";
label3.Text = speed;
}
}
public class DownloaderProgressArgs : EventArgs {
public int DownloadSpeed;
public int speedOutput;
}