Problem in delegate

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Dear,
I want to make delegate following this method like this way but it won't work.

C#

private delegate void CopyFileDelegate(string srcDir, string DesDir);

public void CopyFile(string srcDir, string DesDir)
{
    if (txtLoadPath.InvokeRequired == false)
    {
    }
    else
    {
        txtLoadPath.BeginInvoke(new CopyFileDelegate(CopyFile(srcDir, DesDir)), new object[] {});  // Here is the problem
    }
}

error said method needed.
what's wrong here, what should I do. Please help me. I am new in delegate.
Mahmud

Posted 9-Oct-10 18:00pm

Mahmudunnabi

Updated 11-Oct-10 1:30am

Toli Cuturicu

v4

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AspDotNetDev · Answer 1 · 2010-10-09T18:12:00

Solution 1

You don't specify parameters when creating an instance of a delegate. Look here for some examples of what you are trying to do.

Posted 9-Oct-10 18:12pm

AspDotNetDev

Abhinav S · Answer 2 · 2010-10-09T18:52:00

Solution 2

You could try this -

CopyFileDelegate objD = new CopyFileDelegate(CopyFile);
txtLoadPath.BeginInvoke(objD, new object[] { srcDir , DesDir});

Posted 9-Oct-10 18:52pm

Abhinav S

Ed Guzman · Answer 3 · 2010-10-09T19:41:00

Solution 3

Your txtLoadPath.BeginInvoke accepts a delegate of CopyFileDelegate type as the first parameter. You create an instance of this delegate incorrectly.
Instead of:

<br />
new CopyFileDelegate(CopyFile(srcDir,DesDir))

please write:

<br />
new CopyFileDelegate(CopyFile)

Your code should be:

C#

private delegate void CopyFileDelegate(string srcDir,string DesDir);
       public void CopyFile(string srcDir,string DesDir)
       {
           if (txtLoadPath.InvokeRequired == false)
           {
           }
           else
            {
        txtLoadPath.BeginInvoke(new CopyFileDelegate(CopyFile), new object[] {});
            }
       }

Posted 9-Oct-10 19:41pm

Ed Guzman

Comments

Abhinav S 10-Oct-10 1:51am

I'm a little confused - you are missing the two CopyFile parameters right?

Ed Guzman 10-Oct-10 10:40am

Correct, when you instantiate a delegate (using new keyword), you just point to the name of the function without parameters
Please read my article
<a href="http://www.codeproject.com/KB/cs/delegatespart1.aspx">http://www.codeproject.com/KB/cs/delegatespart1.aspx</a>

AspDotNetDev 10-Oct-10 13:50pm

And how do you expect the parameters to be passed to the function? This will compile, but it will not work.

Ed Guzman 10-Oct-10 15:11pm

Actually the first parameter of the TextBox.BeginInvoke method is System.Delegate, and according to Microsoft this is a delegate to a method that takes no parameters.

AspDotNetDev 11-Oct-10 11:42am

I never said the parameters should be passed via the first parameter of BeginInvoke. CopyFileDelegate can be used in place of type Delegate. The second parameter of BeginInvoke is the array of parameters that will be passed to the first parameter. What did you think it was for and why would it be there if the only overload for this method ignored that array? Like I said, your method will compile, but it will not function correctly, because it's dropping off parameters.

Ed Guzman 11-Oct-10 20:22pm

What I am trying to say is that your private delegate
void CopyFileDelegate(string srcDir,string DesDir)
has the signature that accepts 2 parameters and you use this delegate in BeginInvoke method of a textbox. Which is incorrect, because according to Microsoft this Delegate should be parameter-less. Definitely there is a way to pass parameters but not the way you tried. That is why your code was not compiled at the first.

AspDotNetDev 12-Oct-10 17:57pm

What do you mean by "your code was not compiled at first"? I am not the OP or Abhinav. I am aspdotnetdev. I gave no code. And, yes, you can pass parameters using that delegate and the BeginInvoke technique, as described by Abhinav. You just don't pass them in while constructing the delegate.