FiveTech Software tech support forums

2015-07-31 16:05 UTC-0800 Pritpal Bedi (bedipritpal at hotmail.com)(r417)
+ hbqtqmlparts

+ hbqtqmlparts/resources
+ hbqtqmlparts/resources/png
+ hbqtqmlparts/resources/png/left-32.png
+ hbqtqmlparts/resources/png/refresh-32.png
+ hbqtqmlparts/resources/png/right-32.png
+ hbqtqmlparts/resources/png/stop-32.png
+ hbqtqmlparts/resources/qml
+ hbqtqmlparts/resources/qml/BarcodeReader.qml
+ hbqtqmlparts/resources/qml/WebView.qml
+ hbqtqmlparts/resources/wav
+ hbqtqmlparts/resources/wav/barcode-beep.wav
+ hbqtqmlparts/resources/wav/camera-flash.wav

+ hbqtqmlparts/misc.prg
+ hbqtqmlparts/qmlbridge.prg
+ hbqtqmlparts/barcodereader.prg
+ hbqtqmlparts/webview.prg

+ hbqtqmlparts/hbqtqmlparts.hbc
+ hbqtqmlparts/hbqtqmlparts.hbp
+ hbqtqmlparts/hbqtqmlparts.hbx
+ hbqtqmlparts/hbqtqmlparts.qrc

+ hbqtqmlparts/tests
+ hbqtqmlparts/tests/demobarcodereader.prg
+ hbqtqmlparts/tests/demowebview.prg
+ hbqtqmlparts/tests/hbmk.hbm

+ qtcontribs.hbp
+ Added: hbqtqmlparts/hbqtqmlparts.hbp

Initial commit of Harbour engine for QML manipulation.

QML is the next-generation offering by Qt which facilitates to develop
modern-looking, javaScript based applications. QML is also the core
language adopted by Ubuntu mobile plaforms and its concept of
one-os-fit-all-devices shift. So seems QML is set to become the
protocol of choice for so many applications.

Harbour's implementation of Qt, i.e. HbQt, is essentially a widget
based implementation. It took me a while to turn to QML because
of the necessity to have barcode reading inside my mobile offerings.
I remained reluctant to give QML a try for a long time because of the
complexity how Signal/Slot mechanism is implemented in Harbour.
But when I took initiative, I found that it is simpler than my fear.
Bottom line is : we can start using QML to some extent alsong-with
and within our existing widget based apps.

CLASS HbQtQmlBridge() provides the building blocks to stream-line
the complexity of signal/slots, set/get properties, execute methods, etc.

CLASS HbQtQmlBridge()

METHOD init( oParent )
METHOD create( oParent )

METHOD setQml( cQml ) -> lSuccess
METHOD show() -> NIL
METHOD setProperty( cProperty, xValue ) -> lSuccess
METHOD setChildProperty( cChild, cProperty, xValue ) -> lSuccess
METHOD getProperty( cProperty ) -> oQVariant | NIL
METHOD getChildProperty( cChild, cProperty ) -> oQVariant | NIL
METHOD invokeMethod( cMethod, ... ) -> oQVariant | NIL
METHOD connect( cSignal, bBlock ) -> lSuccess
METHOD connectChild( cChild, cSignal, bBlock ) -> lSuccess

:create() only initiates a QQuickWidget(), set some of its
properties, connects it to error handeling slots and
lays it in a best-judged layout on its parent.

:setQml( cQml ) is where all the action happens.
This is the only place where we could know if a QML
document has been loaded or not. All subsequest operations
are executable only if we succeed here. Be noted that QML
engine is a scripting engine and is based on JavaScript
heavily.

Lets disect CLASS HbQtBarcodeReader() and BarcodeReader.qml in
relevant context only. HbQtBarcodeReader() is developed to provide
one-line calling methodology in mind and has many other constructs
you are already familiar with.

METHOD HbQtBarcodeReader:create( oParent )
...
...
// register C++ classes in order to access them inside QML
// immediately before those are about to be Used
//
HBQAbstractVideoSurface():registerQmlTypes()
QZXing():registerQmlTypes()

::oQmlBridge := HbQtQmlBridge():new():create( ::oQmlContainerWidget )

// provide the QML document location needed
//
IF ::oQmlBridge:setQml( "qrc:/hbqtqml/resources/qml/BarcodeReader.qml" )
::stopCamera()

#ifndef __ANDROID__
// because QVideoProbe() is only available for Android
// we need render the frame ourselves, so this connection
//
::oQmlBridge:connectChild( "videosurface", "imageAvailable(QImage)", {| oImage | ::dispImage( oImage ) } )
#endif
// we could have connected the "qzxing" child also for the same effect
// but we decided to receive signal via QML document as it implements
// more constructs.
//
::oQmlBridge:connect( "tagFound(QString)", {| cTag | ::manageBarcodeFound( cTag ) } )

__hbqtAppRefresh()
ENDIF
...
...
RETURN self


BarcodeReader.qml [ only relevant parts ]:
=========================================

Rectangle {
id : cameraUI
objectName : "camerainterface" // name to access the object
// as this is the root object
// it can be accessed directly.

property bool stopScanningFrames // can be set/get via :setProperty

signal imageCaptured( string image )
signal tagFound( string tag ) // signal we will receive via :connect

function startScanning() {
stopScanningFrames = false;
}
function stopScanning() {
stopScanningFrames = true;
}
function stopCamera() { // method we will invoke via :invokeMethod
cameraUI.stopScanning();
camera.stop();
}
function startCamera() {
camera.start();
cameraUI.startScanning();
myVideoSurface.decoder = decoder;
myVideoSurface.source = camera;
}

Camera {
id: camera
objectName: "camera" // can be accessed as QObject
// from PRG QObject can only be
// exploited via :connect()
}

VideoOutput {
id : viewfinder
objectName : "viewfinder"
source : Qt.platform.os == "android" ? camera : myVideoSurface
}

QZXing{
id : decoder
objectName : "qzxing"
onTagFound : {
if( ! cameraUI.stopScanningFrames )
{
cameraUI.stopScanningFrames = true;
playSoundCameraFlash.play();
cameraUI.tagFound( tag ); // emit the signal which we :connect()ed
}
}
}

HBQAbstractVideoSurface{
id : myVideoSurface
objectName : "videosurface" // will connect via :connectChild()
}

SoundEffect {
id : playSoundCameraFlash
source : "qrc:/hbqtqml/resources/wav/barcode-beep.wav"
}
}

A convinient function, one-liner, can be fired _ a barcode as:
__hbqtActivateBarcodeReader( {|cBarcode| LetMePushIntoField( cBarcode ) } )

I hope this class will flourish with passage of time as we will gain
more experience into QML and allied technology. I am impressed with
results and plan to share with you whatever meaningful I could muster.

Enjoy and stay tuned!


Pritpal Bedi
a student of software analysis & concepts

Pritpal,

Many thanks for telling us

Great job!