> For the complete documentation index, see [llms.txt](https://fearless.gitbook.io/creating-controls-in-assembler/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://fearless.gitbook.io/creating-controls-in-assembler/inside-our-control/on-creation-wmcreate.md).

# 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](https://msdn.microsoft.com/en-us/library/windows/desktop/ms633587%28v=vs.85%29.aspx) api call in our `SimpleButtonRegister` function. See the section [The Memory Used To Store Properties](/creating-controls-in-assembler/control-properties/the-memory-used-to-store-properties.md) for more details on the `__AllocMemProperties`function.

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](/creating-controls-in-assembler/control-properties/property-structures-and-constants.md) 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](/creating-controls-in-assembler/initializing-our-control.md)).

See the [Control Properties](/creating-controls-in-assembler/control-properties.md) section later on for more details on the technical aspect of how we handle setting and getting our control's properties.


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