Home | All Classes | Main Classes | Annotated | Grouped Classes | Functions

Character input in Qt/Embedded

Internally in the client/server protocol, each key press and key release is sent as a QWSKeyEvent. A QWSKeyEvent contains the following fields:

unicode Unicode value
keycode Qt keycode value as defined in qnamespace.h
modifier A bitfield consisting of some of Qt::ShiftButton, Qt::ControlButton, and Qt::AltButton.
is_press TRUE if this is a key press, FALSE if it is a key release.
is_auto_repeat TRUE if this event is caused by auto repeat.

When the server receives a key event it is sent to each client process which is responsible for processing the key event and sending it to the right window, if any. Key events may come from several different sources.

Keyboard drivers

A keyboard driver reads data from a device and gives key events to the server.

Keyboard drivers can be compiled into the library or loaded as plugins. Running ./configure -help lists the available keyboard drivers. The "tty" driver is enabled in the default configuration.

The keyboard drivers all follow the same pattern. They read keyboard data from a device, find out which keys were pressed, and then call the static function QWSServer::processKeyEvent() with the key information.

At present, the console keyboard driver also handles console switching (Ctrl+Alt-F1...Ctrl+Alt+F10) and termination (Ctrl+Alt+Backspace).

To add a keyboard driver for a new device, subclasses of QWSKeyboardHandler and QKbdDriverPlugin can be written and installed as plugins.

Key event filters (input methods)

When the server receives a key event from a keyboard driver, it first passes it through a filter.

This can be used to implement input methods, providing input of characters that are not on the keyboard.

To make an input method, subclass QWSServer::KeyboardFilter (in src/kernel/qwindowsystem_qws.h) and implement the virtual function filter(). If filter() returns FALSE, the event will be sent to the clients (using QWSServer::sendKeyEvent()). If filter() returns TRUE, the event will be stopped. To generate new key events, use QWSServer::sendKeyEvent(). (Do not use processKeyEvent(), since this will lead to infinite recursion.)

To install a keyboard event filter, use QWSServer::setKeyboardFilter(). Currently, only one filter can be installed at a time.

Filtering must be done in the server process.

The launcher example contains an example of a simple input method, SimpleIM which reads a substitution table from a file.

Pen input

Key events do not need to come from a keyboard device. The server process may call QWSServer::sendKeyEvent() at any time.

Typically, this is done by popping up a widget, and letting the user specify characters with the pointer device.

Note: the key input widget should not take focus, since the server would then just send the key events back to the input widget. One way to make sure that the input widget never takes focus is to set the WStyle_Customize and WStyle_Tool widget flags in the QWidget constructor.

The Qtopia environment contains various input widgets such as Handwriting Recognition and Virtual Keyboard.

Copyright © 2005 TrolltechTrademarks
Qt 3.3.7