On Creation: WM_CREATE

We use the WM_CREATE message of our SimpleButton control to initialize the memory that will store blocks of memory for our internal and external variables that will be used by us and by any end-user, and we then call our own initialization routine. I opted to use WM_CREATE instead of WM_NCCREATE because I found over the years that sometimes the cbWndExtra extra data wasn't being allocated sometimes, and any initialization routine that set some defaults values in these extra memory areas could cause an invalid memory address error. I found moving all this code to the WM_CREATE was more reliable.

WM_NCCREATE is one of the first messages a control receives and the WM_NCDESTROY message is one of the last. Its still possible to make use of the WM_NCCREATE message to handle some basic setup of controls, with the above mentioned caveat taken into account.

Our WM_CREATE message of the _SB_WndProc function looks like this:

...
.ELSEIF eax == WM_CREATE
    Invoke __AllocMemProperties, hWin, INTERNAL_PROPERTIES, SIZEOF _SIMPLEBUTTON_PROPERTIES
    Invoke __AllocMemProperties, hWin, EXTERNAL_PROPERTIES, SIZEOF SIMPLEBUTTON_PROPERTIES
    Invoke _SB_Init, hWin
    mov eax, 0
    ret 
...

Our __AllocMemProperties internal helper function handles the allocation of memory for our control's properties and stores pointers to the internal and external properties in the extra window memory reserved by cbWndExtra when the control was registered with the RegisterClassEx api call in our SimpleButtonRegister function. See the section The Memory Used To Store Properties for more details on the __AllocMemPropertiesfunction.

We define and make use of two structures, one prefixed with an underscore for internal properties and the other for use with external properties. See the section Property Structures & Constants for more details.

At the end of the WM_CREATE message we then call our own initialization routine _SB_Init to handle our own setup of our SimpleButton control. At this point we can safely assume the memory allocated for our control has been done so, thus we can call our _SB_Init function to handle the next step (see Initializing Our Control).

See the Control Properties section later on for more details on the technical aspect of how we handle setting and getting our control's properties.