Fix and simplify sensor_explorer example

This commit strives to both fix and simplify the application
and bring its intended demonstrative purpose more forward,
consequently hopefully also making the example easier to
understand and maintain.

First, the sensor_explorer example used QQC1 functionalities
which are no longer available in Qt6. The removed elements were
such that the datamodels needed to be redesigned. This commit
changes the example to use bit more standard Qt model-view
approach.

Second, the sensor_explorer application has not worked in years
on Android due to missing QML plugin installation. While this
could be fixed, in the name of simplicity the example is
now a single binary.

Third, the explorer allowed editing of sensor values. While
this could be a feature of the example, it perhaps deviates
from the gist of the example making it more difficult to
understand. Thus the editing was not added as part of the
example rewrite. It can be added later though.

Task-number: QTBUG-92514
Task-number: QTBUG-92505
Task-number: QTBUG-63054
Change-Id: Icd620ea605a87ba74a42cd1309a3c02d05b146ac
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

3 files changed, 83 insertions, 44 deletions

diff --git a/examples/sensors/sensor_explorer/doc/images/qtsensors-examples-explorer.png b/examples/sensors/sensor_explorer/doc/images/qtsensors-examples-explorer.png
deleted file mode 100644
index 888fc3c6..00000000
--- a/examples/sensors/sensor_explorer/doc/images/qtsensors-examples-explorer.png
+++ /dev/null
diff --git a/examples/sensors/sensor_explorer/doc/images/qtsensors-examples-sensor-explorer.png b/examples/sensors/sensor_explorer/doc/images/qtsensors-examples-sensor-explorer.png
new file mode 100644
index 00000000..830f9597
--- /dev/null
+++ b/examples/sensors/sensor_explorer/doc/images/qtsensors-examples-sensor-explorer.png
diff --git a/examples/sensors/sensor_explorer/doc/src/sensor_explorer.qdoc b/examples/sensors/sensor_explorer/doc/src/sensor_explorer.qdoc
index 367711b1..aef88c39 100644
--- a/examples/sensors/sensor_explorer/doc/src/sensor_explorer.qdoc
+++ b/examples/sensors/sensor_explorer/doc/src/sensor_explorer.qdoc
@@ -31,74 +31,113 @@
     \ingroup qtsensors-examples
     \brief Demonstrates how to read the meta-data of available sensors.
 
-    \image qtsensors-examples-explorer.png
+    \image qtsensors-examples-sensor-explorer.png
 
-    This example is divided into two parts:
+    The example is implemented as a typical model-view application. The
+    models are written with C++ and exposed to QML, and the views are
+    implemented as QML types in the QML application.
 
-    \list
-    \li A \l{Sensor Explorer QML Import}{C++ plugin} that provides QML
-        alternatives for \c QSensorExplorer, \c QPropertyInfo and
-        \c QSensorItem C++ classes.
-    \li A \l{Sensor Explorer QML Application}{QML Application} that uses
-        the QML types to read the sensor meta-data and present it.
-    \endlist
+    \section1 Exposing and Importing the Models
 
-    This example is built as an executable with C++ code that runs the QML,
-    but it can also be launched directly using the \c qmlscene tool. You
-    should build the top-level \e sensor_explorer project before trying to
-    run this example or it will not be able to find its dependencies.
+    The QML models written in C++ are exposed in the project build files
+    as a \c SensorModels QML module.
 
+    \e CMake:
     \code
-    qmlscene -I . sensor_explorer.qml
+    set_target_properties(sensor_explorer PROPERTIES
+        QT_QML_MODULE_VERSION 1.0
+        QT_QML_MODULE_URI SensorModels
+    )
+    qt_qml_type_registration(sensor_explorer)
     \endcode
 
-    Above, the -I . parameter adds the current directory as a module import
-    path to locate the Explorer QML module.
+    \e qmake:
+    \code
+    CONFIG += qmltypes
+    QML_IMPORT_NAME = SensorModels
+    QML_IMPORT_MAJOR_VERSION = 1
+    \endcode
 
-    \section1 Sensor Explorer QML Import
+    The indvidual model elements are exposed as part of the model
+    code by using the \c QML_ELEMENT macro as illustrated here:
+    \snippet sensor_explorer/sensormodels.h 0
 
-    The Sensor Explorer QML import defines the \e Explorer QML module,
-    exporting \c QSensorExplorer, \c QPropertyInfo and \c QSensorItem C++
-    classes as QML types. The source code is available in the
-    \c sensor_explorer/import subdirectory.
+    To access the models in the QML application, the module is imported
+    by the application QML:
+    \snippet sensor_explorer/sensor_explorer.qml 0
 
-    \section1 Sensor Explorer QML Application
+    \section1 Populating the Model of Available Sensors
 
-    To write a QML application that will use the QML types exposed by the
-    Explorer module, following steps are needed:
+    The \c AvailableSensorsModel is a list model that provides information on
+    available sensors on the device. The model is populated once at the
+    element's construction time:
 
-    Import the Explorer 1.0 declarative plugin:
+    \snippet sensor_explorer/sensormodels.cpp 0
 
-    \snippet sensor_explorer/sensor_explorer.qml 0
+    The model's \c data() function returns a pointer to the requested sensor
+    object.
 
-    Create a SensorExplorer QML item:
+    \snippet sensor_explorer/sensormodels.cpp 1
 
-    \snippet sensor_explorer/sensor_explorer.qml 1
+    Since the sensor (QSensor) is a QObject, the QML is then able to directly
+    access all metaproperties and -functions directly.
 
-    You can retrieve a list of all available sensors using
-    \c SensorExplorer.availableSensors:
+    \note It would be possible to refresh the sensor list later at will, but for
+    the simplicity of the example such functionality is not exposed to QML.
 
-    \snippet sensor_explorer/sensor_explorer.qml 2
+    \section1 Populating the Model of Sensor Properties
+
+    The \c SensorPropertyModel is a table model that provides individual
+    sensor's property-value pairs as columns. The column \c 0 provides the
+    property's name and the column \c 1 provides the property's value. The
+    population of the properties is done by reading the metadata of the sensors.
+    The model reads both the sensor's metadata as well as the sensor's reading's
+    metadata. The code below illustrates the reading of the \c reading metadata:
+
+    \snippet sensor_explorer/sensormodels.cpp 2
+
+    This metadata access allows providing the model data for all sensors
+    without prior compile-time understanding of their properties.
 
-    The example uses the returned list as a model to populate a view of
-    available sensors.
+    Once the metadata is set, the code then subscribes to the
+    QSensor::readingChanged() signal to detect sensor reading changes.
+    Upon such changes (for example a rotation value changes), the model data
+    is updated accordingly.
 
-    To retrieve the properties of a sensor, use \c SensorItem.properties:
+    \section1 Viewing the Models
+
+    The QML application is based on two views. The first view shows the available
+    sensors as a selectable list. The second view shows the selected sensor's
+    properties and their values. The delegates for viewing the individual items
+    are simplistic \e {rectangle and text} items.
+
+    Binding the two views functionally together is done by binding the property
+    model's \c sensor property to the current selection of the available sensors
+    model:
+
+    \snippet sensor_explorer/sensor_explorer.qml 1
+
+    When the selected sensor changes, the \c sensor of the property model changes
+    accordingly.
+
+    The following snippet illustrates how the property view is implemented. For
+    more details about QML models and views, please see
+    \l{Models and Views in Qt Quick}.
 
     \snippet sensor_explorer/sensor_explorer.qml 3
 
-    The property list is used as a model for another view that displays the
-    property names and values.
+    For clarity it should be mentioned that the \c display attribute used by
+    the text element refers to the Qt::DisplayRole role of the model, which is
+    provided by default by Qt models.
 
-    It is possible to edit the values of certain sensor properties. Selecting
-    a writable property value will open an editor. \c SensorExplorer QML
-    type allows you to pass a new value for a sensor property value as
-    follows:
+    \section1 Activating the Sensors
 
-    \snippet sensor_explorer/sensor_explorer.qml 4
+    The example has a button for activating and deactivating the currently
+    selected sensor. The button is enabled only if a sensor is currently
+    selected, as illustrated below.
+
+    \snippet sensor_explorer/sensor_explorer.qml 2
 
-    Starting and stopping a sensor can be done by setting the
-    \c SensorItem.start property:
+    On clicking the button, the sensor's active property is toggled on/off.
 
-    \snippet sensor_explorer/sensor_explorer.qml 5
 */