> 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-destroying-wmncdestroy.md).

# On Destroying: WM\_NCDESTROY

When the control is destroyed we free the memory we allocated and call a cleanup routine for any other business (if required). Note our `_SB_Cleanup` function in our `WM_NCDESTROY` message (shown below,) is called **first** whilst the memory for our variables/properties still exists - This is important in case we have to free any other resources, handles or objects that we have stored previously in our internal or external properties.

```
...
.ELSEIF eax == WM_NCDESTROY
    Invoke _SB_Cleanup, hWin ; cleanup any other stuff as required
    Invoke __FreeMemProperties, hWin, INTERNAL_PROPERTIES
    Invoke __FreeMemProperties, hWin, EXTERNAL_PROPERTIES
    mov eax, 0
    ret
...
```

Our internal helper function `__FreeMemProperties` used [GetWindowLong](https://msdn.microsoft.com/en-us/library/windows/desktop/ms633584%28v=vs.85%29.aspx) to retrieve the appropriate pointer for the internal and external memory blocks used to store our variables and then frees that memory with calls to [GlobalFree](https://msdn.microsoft.com/en-us/library/windows/desktop/aa366579%28v=vs.85%29.aspx).