# `wxBookCtrlEvent`
[🔗](https://github.com/erlang/otp/blob/master/lib/wx/src/gen/wxBookCtrlEvent.erl#L58)

This class represents the events generated by book controls (`m:wxNotebook`, `m:wxListbook`, `m:wxChoicebook`, `m:wxTreebook`, `m:wxAuiNotebook`).

The PAGE_CHANGING events are sent before the current page is changed. It allows the
program to examine the current page (which can be retrieved with `getOldSelection/1`) and to veto the page
change by calling `wxNotifyEvent:veto/1` if, for example, the current values in the controls of the old page are invalid.

The PAGE_CHANGED events are sent after the page has been changed and the program cannot
veto it any more, it just informs it about the page change.

To summarize, if the program is interested in validating the page values before allowing
the user to change it, it should process the PAGE_CHANGING event, otherwise PAGE_CHANGED
is probably enough. In any case, it is probably unnecessary to process both events at once.

See:
* `m:wxNotebook`

* `m:wxListbook`

* `m:wxChoicebook`

* `m:wxTreebook`

* `m:wxToolbook`

* `m:wxAuiNotebook`

This class is derived, and can use functions, from:

* `m:wxNotifyEvent`

* `m:wxCommandEvent`

* `m:wxEvent`

wxWidgets docs: [wxBookCtrlEvent](https://docs.wxwidgets.org/3.2/classwx_book_ctrl_event.html)

# `wxBookCtrl`

```erlang
-type wxBookCtrl() ::
          #wxBookCtrl{type :: wxBookCtrlEvent:wxBookCtrlEventType(),
                      nSel :: integer(),
                      nOldSel :: integer()}.
```

# `wxBookCtrlEvent`

```erlang
-type wxBookCtrlEvent() :: wx:wx_object().
```

# `wxBookCtrlEventType`

```erlang
-type wxBookCtrlEventType() ::
          command_notebook_page_changed | command_notebook_page_changing | choicebook_page_changed |
          choicebook_page_changing | treebook_page_changed | treebook_page_changing |
          toolbook_page_changed | toolbook_page_changing | listbook_page_changed |
          listbook_page_changing.
```

# `getOldSelection`

```erlang
-spec getOldSelection(This) -> integer() when This :: wxBookCtrlEvent().
```

Returns the page that was selected before the change, `wxNOT\_FOUND` if none was
selected.

# `getSelection`

```erlang
-spec getSelection(This) -> integer() when This :: wxBookCtrlEvent().
```

Returns the currently selected page, or `wxNOT\_FOUND` if none was selected.

Note: under Windows, `getSelection/1` will return the same value as `getOldSelection/1` when called from the `EVT_BOOKCTRL_PAGE_CHANGING`
handler and not the page which is going to be selected.

# `setOldSelection`

```erlang
-spec setOldSelection(This, Page) -> ok when This :: wxBookCtrlEvent(), Page :: integer().
```

Sets the id of the page selected before the change.

# `setSelection`

```erlang
-spec setSelection(This, Page) -> ok when This :: wxBookCtrlEvent(), Page :: integer().
```

Sets the selection member variable.

---

*Consult [api-reference.md](api-reference.md) for complete listing*
