Lambda expression in C++/CLI Winform

Question

0.00/5 (No votes)

See more:

Hi,

could somebody tell me how can I write following codes in C++/CLI WinForm?
I've searched two days and tried several times, but without success.

C#

private void OnOpenForm2Click(object sender, EventArgs e)
{
   var form2Obj = new Form2();
   form2Obj.Shown += (o, args) => { btnOpenForm2.Enabled = false; };
   form2Obj.FormClosed += (o, args) => { btnOpenForm2.Enabled = true; };
   form2Obj.Show();
}

Posted 30-Oct-12 23:22pm

christmars

Updated 31-Oct-12 3:31am

v2

Add a Solution

Comments

Sergey Alexandrovich Kryukov 31-Oct-12 9:46am

You don't need lambda here so much, you need anonymous delegates. First of all, you can do it with "regular" named functions. If you need anonymous, which is way better in this case, you need the version of C++/CLI of VS2010 or later. What do you use?
--SA

christmars 31-Oct-12 10:23am

Yes the version I am using is VS2010. But I don't really understand how to use the "anonymous delegates" under c++/cli.

I've tried :

form2Obj->Shown += delegate(System::Object^ o, System::EventArgs^ args ) => {btnOpenForm2->Enabled = false;};

which didn't work...

Sergey Alexandrovich Kryukov 31-Oct-12 10:52am

The syntax is a bit different -- please see the article I referenced in my answer.
--SA

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Accepted Answer · 2012-10-31T04:02:00

Solution 1

Lambda expressions are introduced in C++11:
http://en.wikipedia.org/wiki/C%2B%2B11#Lambda_functions_and_expressions[^].

More exactly, what you need is anonymous methods. Please see:
http://en.wikipedia.org/wiki/Anonymous_function#C.2B.2B[^].

If your version of C++/CLI is new enough, you can use it on C++/CLI as well.

Please see also this article:
Using lambdas - C++ vs. C# vs. C++/CX vs. C++/CLI[^].

And also see my comment to the question. In worst case, if you just want the functionality or the code you show, you can always define separate named functions FormShownHandler(System::Object, System::EventHandler) and FormClosedHandler(System::Object, System.Windows.Forms::FormClosedEventArgs) instead of anonymous methods.

—SA

Posted 31-Oct-12 4:02am

Sergey Alexandrovich Kryukov

Updated 31-Oct-12 5:24am

v2

Comments

christmars 31-Oct-12 10:41am

So I still can't make it. I tried:

form2Obj->Shown += gcnew FormShownHandler(System::Object, System::EventArgs) => {btnOpenForm2->Enabled = false;};

The error is, FormShownHandler is not identified.
Could you please show what you would write? What you meant is right, but I need to see the form for the functionality!

Sergey Alexandrovich Kryukov 31-Oct-12 10:48am

No! You did not get it. In this case, FormShownHandler should be a function defined separately.

But OK, your version of C++/CLI is new enough. Use the anonymous delegate syntax shown in the article I referenced -- it will work. Locate this code snippet in this article:
RunFoo( [](int x) -> int { return x; });

--SA

christmars 31-Oct-12 11:08am

Sorry I didn't see the reference. I would read the article you give me carefully.
Thank you!

Sergey Alexandrovich Kryukov 31-Oct-12 11:20am

You are very welcome.
Good luck, call again.
--SA

Sergey Alexandrovich Kryukov 31-Oct-12 11:26am

After I saw your clarification on VS2010, it became clear that you can keep anonymous methods in C++/CLI, as you can use new features of C++11.

I found that Wikipedia covers this topic really well, with syntax and samples. Please see my updated answer.
--SA

christmars 1-Nov-12 4:26am

Hi SA,I have read the articles. And I think your suggestion is like this:

//firstlly I declared Form to be openedauto Form^ form2Obj = gcnew Form2();

//Then, define FormShownHandler(here use the anonymous method)

//Although refers to the wiki samples, I didn't define this succesfully:

auto FormShownHandler = [ ] ( ) { button->Enabled=false; };

//After that, use the self created FormShownHandler instead of the system defined one:

form2Obj->Shown += FormShownHandler;

Have I gotten your idea? The use of anonymous function was wrong, could you help?

christmars 1-Nov-12 5:08am

Hi SA,
I got it!
Codes:

//make two funktions for EventHandler:
public : void DisableButton1(System::Object ^,System::EventArgs ^)
{this->button1->Enabled=false;}
public : void EnableButton(System::Object ^,System::EventArgs ^)
{this->button1->Enabled=true;}

private :System::Void button1_Click(System::Object^ sender, System::EventArgs^ e)
{
Form^ form2Obj = gcnew Form2();
form2Obj->Shown += gcnew System::EventHandler(this, &Form1::DisableButton1);
form2Obj->Closed += gcnew System::EventHandler(this, &Form1::EnableButton1);
form2Obj->Show();
}

I did't use anonymous methods to solve this problem, but without your advices I couldn't know where was my mistake. Thanks again for the articles you gave me, they are helpful!

Sergey Alexandrovich Kryukov 1-Nov-12 11:15am

Well, I would always prefer anonymous method, because they simplify code and improve maintenance. You better learn using them.
But I'm so glad you can do the solution now.

You are very welcome.
Good luck, call again.
--SA