MessageFilter problem with overriding

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I tryed to buid a MessageFilter, but I don't know how to override the PreFilterMessage method correctly.

I tryed:

public ref class MyMessageFilter : System::Windows::Forms::IMessageFilter{
public: MyMessageFilter(){
    }
virtual bool PreFilterMessage(Message^objMessage) override{
                    if(objMessage->WParam.ToInt32() == 27)
                        return true;
                    return false;
            }
};

But I get an error:
error C3766: "MyMessageFilter" muss eine Implementierung für die bool System::Windows::Forms::IMessageFilter::PreFilterMessage (System::Windows::Forms::Message %)-Schnittstellenmethode bereitstellen.

What am I doing wrong? Thanks for your help!

Posted 3-Aug-10 3:56am

egon_ll

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2 solutions

Solution 3

It still gives the same error:

error C3766: 'MyMessageFilter' must provide an implementation for the interface method 'bool System::Windows::Forms::IMessageFilter::PreFilterMessage(System::Windows::Forms::Message %)'

Posted 3-Aug-10 22:41pm

egon_ll

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E.F. Nijboer · Accepted Answer · 2010-08-03T04:33:00

Solution 1

You did not declare the method to override. You tell the compiler you are declaring it for the first time and with virtual you indicate it could be overridden using override.

Try this:

public ref class MyMessageFilter : System::Windows::Forms::IMessageFilter{public: MyMessageFilter(){    }

override bool PreFilterMessage(Message^objMessage) override{                    
   return objMessage->WParam.ToInt32() == 27;
}
};

http://msdn.microsoft.com/en-us/library/9fkccyh4(VS.71).aspx[^]

Good luck!

Posted 3-Aug-10 4:33am

E.F. Nijboer

Updated 3-Aug-10 4:34am

v2

Comments

egon_ll 3-Aug-10 15:52pm

I think there is still a mistake. Now I get three more errors:

error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
error C2217: "override" requires "virtual"
error C2144: 'bool' should be preceded by ';'

E.F. Nijboer 4-Aug-10 3:30am

My german error messages aren't that good ;-) But I also made a mistake myself because you implement an interface and are not declaring a subclass. It should be:
public bool PreFilterMessage(Message^objMessage) {...}
I guess it should already go better with this declaration. Let me no if this raises any other errors.

egon_ll 6-Aug-10 3:05am

Sorry I forgot to translate them. But I did now. Still the same error...

E.F. Nijboer 6-Aug-10 4:10am

Seems like you where right about the virtual bool PreFilterMessage, but without the override. Have a look at this example, I think this might help. http://msdn.microsoft.com/en-us/library/ms171538.aspx

egon_ll 6-Aug-10 9:27am

Thank you!! That really helped me! It had to be:
virtual bool PreFilterMessage(Message%m)