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\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
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
\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
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
\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.
\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
\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
\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.
\section1 MyInputPanel Class Implementation
If we look at the constructor first, we have a lot of signals 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
\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
\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.