/**************************************************************************** ** ** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies). ** All rights reserved. ** Contact: Nokia Corporation (qt-info@nokia.com) ** ** This file is part of the documentation of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:FDL$ ** GNU Free Documentation License ** Alternatively, this file may be used under the terms of the GNU Free ** Documentation License version 1.3 as published by the Free Software ** Foundation and appearing in the file included in the packaging of ** this file. ** ** Other Usage ** Alternatively, this file may be used in accordance with the terms ** and conditions contained in a signed written agreement between you ** and Nokia. ** ** ** ** ** $QT_END_LICENSE$ ** ****************************************************************************/ /*! \example tools/inputpanel \title Input Panel Example The Input Panel example shows how to create an input panel that can be used to input text into widgets using only the pointer and no keyboard. \image inputpanel-example.png The input fields in the main window have no function other than to accept input. The main focus is on how the extra input panel can be used to input text without the need for a real keyboard or keypad. \section1 Main Form Class Definition Because the main window has no other function than to accept input, it has no class definition. Instead, its whole layout is made in Qt Designer. This emphasizes the point that no widget specific code is needed to use input panels with Qt. \section1 MyInputPanelContext Class Definition \snippet examples/tools/inputpanel/myinputpanelcontext.h 0 The \c MyInputPanelContext class inherits QInputContext, which is Qt's base class for handling input methods. \c MyInputPanelContext is responsible for managing the state of the input panel and sending input method events to the receiving widgets. The \c inputPanel member is a pointer to the input panel widget itself; in other words, the window that will display the buttons used for input. The \c identifierName(), \c language(), \c isComposing() and \c reset() functions are there mainly to fill in the pure virtual functions in the base class, QInputContext, but they can be useful in other scenarios. The important functions and slots are the following: \list \o \c filterEvent() is where we receive events telling us to open or close the input panel. \o \c sendCharacter() is a slot which is called when we want to send a character to the focused widget. \o \c updatePosition() is used to position the input panel relative to the focused widget, and will be used when opening the input panel. \endlist \section1 MyInputPanelContext Class Implementation In the constructor we connect to the \c characterGenerated() signal of the input panel, in order to receive key presses. We'll see how it works in detail later on. \snippet examples/tools/inputpanel/myinputpanelcontext.cpp 0 In the \c filterEvent() function, we must look for the two event types: \c RequestSoftwareInputPanel and \c CloseSoftwareInputPanel. \snippet examples/tools/inputpanel/myinputpanelcontext.cpp 1 The first type will be sent whenever an input capable widget wants to ask for an input panel. Qt's input widgets do this automatically. If we receive that type of event, we call \c updatePosition() \mdash we'll see later on what it does \mdash then show the actual input panel widget. If we receive the \c CloseSoftwareInputPanel event, we do the opposite, and hide the input panel. \snippet examples/tools/inputpanel/myinputpanelcontext.cpp 2 We implement the \c sendCharacter() function so that it sends the supplied character to the focused widget. All QInputContext based classes are always supposed to send events to the widget returned by QInputContext::focusWidget(). Note the QPointer guards to make sure that the widget does not get destroyed in between events. Also note that we chose to use key press events in this example. For more complex use cases with composed text it might be more appropriate to send QInputMethodEvent events. The \c updatePosition() function is implemented to position the actual input panel window directly below the focused widget. \snippet examples/tools/inputpanel/myinputpanelcontext.cpp 3 It performs the positioning by obtaining the coordinates of the focused widget and translating them to global coordinates. \section1 MyInputPanel Class Definition The \c MyInputPanel class inherits QWidget and is used to display the input panel widget and its buttons. \snippet examples/tools/inputpanel/myinputpanel.h 0 If we look at the member variables first, we see that there is \c form, which is made with Qt Designer, that contains the layout of buttons to click. Note that all the buttons in the layout have been declared with the \c NoFocus focus policy so that we can maintain focus on the window receiving input instead of the window containing buttons. The \c lastFocusedWidget is a helper variable, which also aids in maintaining focus. \c signalMapper is an instance of the QSignalMapper class and is there to help us tell which button was clicked. Since they are all very similar this is a better solution than creating a separate slot for each one. The functions that we implement in \c MyInputPanel are the following: \list \o \c event() is used to intercept and manipulate focus events, so we can maintain focus in the main window. \o \c saveFocusWidget() is a slot which will be called whenever focus changes, and allows us to store the newly focused widget in \c lastFocusedWidget, so that its focus can be restored if it loses it to the input panel. \o \c buttonClicked() is a slot which will be called by the \c signalMapper whenever it receives a \c clicked() signal from any of the buttons. \endlist \section1 MyInputPanel Class Implementation If we look at the constructor first, we have a lot of signals to connect to! We connect the QApplication::focusChanged() signal to the \c saveFocusWidget() signal in order to get focus updates. Then comes the interesting part with the signal mapper: the series of \c setMapping() calls sets the mapper up so that each signal from one of the buttons will result in a QSignalMapper::mapped() signal, with the given widget as a parameter. This allows us to do general processing of clicks. \snippet examples/tools/inputpanel/myinputpanel.cpp 0 The next series of connections then connect each button's \c clicked() signal to the signal mapper. Finally, we create a connection from the \c mapped() signal to the \c buttonClicked() slot, where we will handle it. \snippet examples/tools/inputpanel/myinputpanel.cpp 3 In the \c buttonClicked() slot, we extract the value of the "buttonValue" property. This is a custom property which was created in Qt Designer and set to the character that we wish the button to produce. Then we emit the \c characterGenerated() signal, which \c MyInputPanelContext is connected to. This will in turn cause it to send the input to the focused widget. In the \c saveFocusWidget() slot, we test whether the newly focused widget is a child of the input panel or not, using the QWidget::isAncestorOf() call. \snippet examples/tools/inputpanel/myinputpanel.cpp 2 If it isn't, it means that the widget is outside the input panel, and we store a pointer to that widget for later. In the \c event() function we handle QEvent::WindowActivate event, which occurs if the focus switches to the input panel. \snippet examples/tools/inputpanel/myinputpanel.cpp 1 Since we want avoid focus on the input panel, we immediately call QWidget::activateWindow() on the widget that last had focus, so that input into that widget can continue. We ignore any other events that we receive. \section1 Setting the Input Context The main function for the example is very similar to those for other examples. The only real difference is that it creates a \c MyInputPanelContext and sets it as the application-wide input context. \snippet examples/tools/inputpanel/main.cpp main With the input context in place, we set up and show the user interface made in Qt Designer before running the event loop. \section1 Further Reading This example shows a specific kind of input context that uses interaction with a widget to provide input for another. Qt's input context system can also be used to create other kinds of input methods. We recommend starting with the QInputContext documentation if you want to explore further. */