QVirtualKeyboardTrace Class

Trace is a data model for touch input data. More...

Header:	#include <QVirtualKeyboardTrace>
qmake:	QT += virtualkeyboard
Since:	QtQuick.VirtualKeyboard 2.0
Instantiated By:	Trace
Inherits:	QObject

This class was introduced in QtQuick.VirtualKeyboard 2.0.

• List of all members, including inherited members

Properties

canceled : bool channels : QStringList final : bool

length : const int opacity : qreal traceId : int

Public Functions

int	addPoint(const QPointF &point)
QVariantList	channelData(const QString &channel, int pos = 0, int count = -1) const
QStringList	channels() const
bool	isCanceled() const
bool	isFinal() const
int	length() const
qreal	opacity() const
QVariantList	points(int pos = 0, int count = -1) const
void	setCanceled(bool canceled)
void	setChannelData(const QString &channel, int index, const QVariant &data)
void	setChannels(const QStringList &channels)
void	setFinal(bool final)
void	setOpacity(qreal opacity)
void	setTraceId(int id)
int	traceId() const

Signals

void	canceledChanged(bool isCanceled)
void	channelsChanged()
void	finalChanged(bool isFinal)
void	lengthChanged(int length)
void	opacityChanged(qreal opacity)
void	traceIdChanged(int traceId)

Detailed Description

Trace provides the data model for coordinate data and other optional data associated with a single stroke.

A typical use case for the trace object is as follows:

• TraceInputArea or other input device initiates the trace event by calling InputEngine.traceBegin() method.
• If the current input method accepts the event it creates a trace object and configures the required data channels (if any).
• TraceInputArea collects the data for the Trace object.
• TraceInputArea calls the InputEngine.traceEnd() method to finish the trace and passing the trace object back to input method.
• The input method processes the data and discards the object when it is no longer needed.

The coordinate data is retrieved using the points() function.

In addition to coordinate based data, it is possible to attach an arbitrary data channel for each data point.

The data channels must be defined before the points are added. The data channels supported by the TraceInputArea are listed below:

• "t" Collects time for each data point. The time is the number of milliseconds since 1970/01/01:

For example, to configure the object to collect the times for each point:

QVirtualKeyboardTrace *trace = new QVirtualKeyboardTrace(this);
trace->setChannels(QStringList() << "t");

The collected data can be accessed using the channelData() function:

QVariantList timeData = trace->channelData("t");

QVirtualKeyboardTrace objects are owned by their creator, which is the input method in normal case. This means the objects are constructed in the InputMethod.traceBegin() (QML) method.

By definition, the trace object can be destroyed at earliest in the InputMethod.traceEnd() (QML) method.

Member Function Documentation

int QVirtualKeyboardTrace::addPoint(const QPointF &point)

Adds a point to the QVirtualKeyboardTrace.

The method returns index of the point added, or -1 if the points cannot be added (i.e. the final is true).

Note: The returned index is required to associate additional data with the point using the setChannelData() method.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

QVariantList QVirtualKeyboardTrace::channelData(const QString &channel, int pos = 0, int count = -1) const

Returns data from the specified channel. If no other parameters are given, the method returns all the data.

If the pos parameter is given, the method returns data starting at the position. The count parameter limits how many items are returned.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

See also setChannelData().

QVariantList QVirtualKeyboardTrace::points(int pos = 0, int count = -1) const

Returns list of points. If no parameters are given, the method returns all the data.

If the pos parameter is given, the method returns points starting at the position. The count parameter limits how many points are returned.

The returned list contains QPointF types.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

void QVirtualKeyboardTrace::setChannelData(const QString &channel, int index, const QVariant &data)

Sets data for the point at index in the given data channel.

If this method is not called for each data point, the channel data will be padded with empty values. However, the data cannot be added at arbitrary index, i.e., it must be added in synchronously with the point data.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

See also channelData().