Provides code snippets to show you how to use a change notifier.
To use a change notifier, a thread:
constructs an RChangeNotifier handle
and then calls its Create() member function to create the
associated Kernel side object. The RChangeNotifier handle
is thread-relative which means that the handle is closed
if the thread dies.
issues a request to
be notified when the next change occurs, passing a TRequestStatus object.
This is a call to the Logon() function.
When a change occurs, the change information is made available to the thread
through the TRequestStatus object and the thread's request
semaphore is signalled to indicate that the request is complete.
The following code fragments demonstrates this:
{
...
RChangeNotifier the_notifier;
TRequestStatus the_status;
...
the_notifier.Create();
the_notifier.Logon(the_status);
User::WaitForRequest(the_status);
...
...// prepare for a long wait
...
TInt changes = the_status.Int();
if (changes & EChangesSystemTime)
{
// handle a change to system time
}
if (changes & EChanges EChangesLocale)
{
// handle a change to locale
}
...
the_notifier.Close();
...
}
In practical code, an RChangeNotifier would be part of
an active object.
The RChangeNotifier handle also offers the LogonCancel() function.
Calling this function, causes the thread's request semaphore to
be signalled and any wait to complete. The TRequestStatus is
set to KErrCancel.
The above technique for checking changes is used because, at the completion of a notification request, any, or all, changes may be reported. Code should make no assumptions about the other bits in the returned value. In other words, code should be prepared for a notification request to complete without an 'interesting' change.
Users should also note that the first notification request after creation
of an RChangeNotifier, completes immediately; the
changes reported are all those defined by the TChanges enum.
Also note that after a notification request completes, other changes may
occur before the user of the RChangeNotifier can issue the
next notification request. If this occurs, any change events are collected
by the change notifier; they are not lost; in this situation, the next notification
request completes immediately.