Sharing wxDEFINE_EVENT in two cpp fiels

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philm
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Sharing wxDEFINE_EVENT in two cpp fiels

Post by philm » Mon May 08, 2017 4:50 pm

Hello all,

I am currently trying to create my own event so that I can propagate coordinate positions from the canvas to the parent class so that I can display the position of the mouse pointer on the frame of the application.

I am using this site as a reference: https://wiki.wxwidgets.org/Custom_Events

At the site, I am using the following code:

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wxDEFINE_EVENT(MY_NEW_TYPE, wxCommandEvent);

wxCommandEvent event(MY_NEW_TYPE); // No specific id
 
// Add any data; sometimes the only information needed at the destination is the arrival of the event itself
event.SetString("This is the data");
 
// Then post the event
wxPostEvent(this, event); // to ourselves
wxPostEvent(pBar, event); // or to a different instance or class
The code above would be in my canvas class.

The code below is what I have defined in my main frame class (The parent):

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wxBEGIN_EVENT_TABLE(MyFoo, wxFoo))
  EVT_COMMAND(wxID_ANY, MY_NEW_TYPE, MyFoo::OnMyEvent)
  ...
wxEND_EVENT_TABLE()
I am using this as a foundation for writing my the coordinate of the mouse cursor to my main frame so that it can be displayed on the screen. I would also like to note that I converted my coordinate position into a string and I already have the string formatted to what I want. This is currently replacing the value "This is the data"

My small issue that I am running into is that my main frame class will not be able to know what is MY_NEW_TYPE since the canvas class and the main frame class use different .cpp file. With wxDefine_EVENT only being used in one class, what is hte best solution to define the Event in my main class so that the main frame class will be able to understand the MY_NEW_TYPE?

DavidHart
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Re: Sharing wxDEFINE_EVENT in two cpp fiels

Post by DavidHart » Mon May 08, 2017 5:22 pm

Hi,

See the mentions of wxDECLARE_EVENT on that wiki page.

Regards,

David

philm
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Re: Sharing wxDEFINE_EVENT in two cpp fiels

Post by philm » Wed May 10, 2017 9:31 pm

If you are refereing to this
You must define the wxEventType exactly once. If you add wxDEFINE_EVENT(MY_NEW_TYPE, wxCommandEvent); to two files, it will be defined twice with two different values. The same thing will happen if you write it only once, but you put it in a header file that is #included more than once. Why does that matter? Because you'll be posting an event with the type (e.g.) 12000, and trying to catch events with type 12001; which will silently fail.
I am aware of this. My issue is that I would need to define MY_NEW_TYPE in the cpp file that actually posts the event and in the cpp file that will catch the event since the class that posts the event will not be the class that catches. I apologize if my question is not very clear. With this rule in mind, how would I define MY_NEW_TYPE in the class that with catch the event?

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doublemax
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Re: Sharing wxDEFINE_EVENT in two cpp fiels

Post by doublemax » Wed May 10, 2017 9:43 pm

My issue is that I would need to define MY_NEW_TYPE in the cpp file that actually posts the event and in the cpp file that will catch the event since the class that posts the event will not be the class that catches.
There is a big difference between defining and declaring. Like already said, wxDEFINE_EVENT must only exist once, because that's the line that gives MY_NEW_TYPE its value. wxDECLARE_EVENT however, can be seen by the compiler multiple times, it just means "there's a value for MY_NEW_TYPE defined somewhere. Go find it and use it".

So, you put wxDEFINE_EVENT in the .cpp file and the matching wxDECLARE_EVENT in the .h file. Where ever you want to use that event, you just include the header file.
Use the source, Luke!

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Re: Sharing wxDEFINE_EVENT in two cpp fiels

Post by MagickPanda » Thu May 11, 2017 11:36 am

doublemax wrote:
My issue is that I would need to define MY_NEW_TYPE in the cpp file that actually posts the event and in the cpp file that will catch the event since the class that posts the event will not be the class that catches.
There is a big difference between defining and declaring. Like already said, wxDEFINE_EVENT must only exist once, because that's the line that gives MY_NEW_TYPE its value. wxDECLARE_EVENT however, can be seen by the compiler multiple times, it just means "there's a value for MY_NEW_TYPE defined somewhere. Go find it and use it".

So, you put wxDEFINE_EVENT in the .cpp file and the matching wxDECLARE_EVENT in the .h file. Where ever you want to use that event, you just include the header file.
Thanks for the explanation, I think I have a few instances of wxDEFINE_EVENT and wxDECLARE_EVENT in the wrong source file or getting included more than once, I will fix that kind of problem asap.

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Re: Sharing wxDEFINE_EVENT in two cpp fiels

Post by ollydbg23 » Wed Feb 24, 2021 10:13 am

Today, I found a similar issue, I see that I should use this:

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wxDECLARE_EXPORTED_EVENT(__declspec(dllexport), MyEventType, MyEvent);
With this code, I can export the event type from the dll, and the other client link to the dll can use it, otherwise, there will be a linker error.

Hope that this can help others.

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