WPEPlatform.ScreenSyncObserver.add_callback

### Method

# WPEPlatform ScreenSyncObserveradd_callback

#### Declaration [src]

    guint
    wpe_screen_sync_observer_add_callback (
      WPEScreenSyncObserver* observer,
      WPEScreenSyncObserverSyncFunc sync_func,
      gpointer user_data,
      GDestroyNotify destroy_notify
    )

#### Description [src]

Add a `sync_func` to be called from a secondary thread when the screen sync is triggered.

To remove this callback pass the identifier that is returned by this function to wpe_screen_sync_observer_remove_callback().

#### Parameters

`sync_func`

  Type: `WPEScreenSyncObserverSyncFunc`

  A `WPEScreenSyncObserverSyncFunc`.

`user_data`

  Type: `gpointer`

  Data to pass to `sync_func`.

  The argument can be `NULL`.
  The data is owned by the caller of the method.

`destroy_notify`

  Type: `GDestroyNotify`

  Function for freeing `user_data` or `NULL`.

  The argument can be `NULL`.

#### Return value

Type: `guint`

An identifier for this callback.