Hi Superpelican
I had almost forgotten PropertyChanged!
It was a nonsense example to show 4 different ways of doing the same
thing, to prove / disprove that all 4 options work.
In a real life application that actually does something useful you
would only use one of the 4 options to respond to one change.
Comment things in and out, and you will see that all 4 approaches are
independent.
What I was trying to show is that you can respond to a change in a
property (both QML native, and one imported from C++) by either direct
binding, or in response to an onXxxxChanged signal / event handler.
Whether you use a binding, or an onXxxxChanged signal is a matter of
taste and horses for courses.
If your changes are simple and few in number, then binding is a good option.
If you want to change lots of things, with complex logic, then
grouping all of this together in an onXxxxChanged or even a State
might be the better option.
I vaguely remember finding cases where binding did not work as
expected, but can't remember what these were.
From a software engineering / architectural point of view it also
depends on where you wish to embed control and knowledge of other
items. Should the thing doing the change be in control
(onXxxxChanged), or the thing that changes (the binding approach)?
I can't really comment on if there are c++ alternatives to the plugin
approach. My c++ programming follows the cut and paste school. In
Harmattan and Sailfish I have successfully made several c++ plugins as
a last resort approach when I have found no clean way to achieve the
same with QML / javascript. So far Plugins have worked for me.
Zitat von Superpelican <superpeli...@zoho.com>:
Hi everyone,
I've been looking at the PropertyChanged project again and do I need
to use both the Q_PROPERTY stuff and the method/signals way? Or can
I just use 1 of them?
Also do I need to make a plugin of the C++ part of my application or
is there also another way to do it?
Kind Regards,
Superpelican
On 05/09/2013 04:30 PM, christopher.l...@thurweb.ch wrote:
Hi SuperPelican
After a little playing around, I have created a minimal SailfishOS
app that demonstrates interaction between a c++ plugin and
SailfishOS QML UI elements.
Once again I have gone the QmlRegisterType / plugin approach. The
app itself is the default SailfishOS QML project, with a few minor
changes.
The app has a SailfishOS PullDownMenu. If you click on the MenuItem
"increment counters", four QML labels have their values changed,
each by a different approach.
When the MenuItem is clicked, it actually updated 2 properties, one
QML "FirstPage.qmlCounter"; and one "cppCounter" exposed by the C++
plugin CPlusPlusCounter 1.0 (which is instantiated as a QML object
myCPlusPlusCounter.
1) "qml.counter binding" is a simple binding to the QML property
"qmlCounter" (no C++)
2) "qml.counter onChanged" is changed by the "onQmlCounterChanged"
event of the same QML property (no C++)
3) "myCPlusPlusCounter binding" is a binding to the property
"cppCounter" exposed by the C++ plugin
4) "myCPlusPlusCounter onChanged" is changed by the
"onCppCounterChanged" event of the same C++ plugin property
All the QML changes are in FirstPage.qml
C++ required minor changes to main.cpp ( qmlRegisterType entry + includes)
and the new files cpluspluscounter.h / .cpp
You should find the entire project as an attachment to this post.
I hope this helps
Chris
Zitat von Superpelican <superpeli...@zoho.com>:
I'm trying to create a hybrid QML/C++ application, where the logic
is written in C++ and the interface is QML/Sailfish Silica based.
I'm currently playing around with the different ways to let
QML/C++ communicate with each other. I currently have this code:
<code>
#include <QApplication>
#include <QGraphicsObject>
#include <QDir>
#include <QDeclarativeView>
#include <QDeclarativeContext>
#include <QDeclarativeEngine>
#include <QDeclarativeComponent>
#include <QDebug>
#include <QDeclarativePropertyMap>
#ifdef HAS_BOOSTER
#include <MDeclarativeCache>
#endif
Q_DECL_EXPORT int main(int argc, char *argv[])
{
#ifdef HAS_BOOSTER
QScopedPointer<QApplication>
myapp(MDeclarativeCache::qApplication(argc, argv));
#else
QScopedPointer<QApplication> myapp = new QApplication(argc, argv);
#endif
#ifdef HAS_BOOSTER
QScopedPointer<QDeclarativeView>
appview(MDeclarativeCache::qDeclarativeView());
#else
QScopedPointer<QDeclarativeView>(new QDeclarativeView);
#endif
QDeclarativePropertyMap binding_map;
binding_map.insert("question_txt", QVariant(QString("5 * 5 =")));
binding_map.insert("color", QVariant(QString("dark red")));
QScopedPointer<QDeclarativeContext>
binding_context(appview->rootContext());
binding_context->setContextProperty("binding_map", &binding_map);
QString file = "main.qml";
QString path = QString(DEPLOYMENT_PATH);
appview->setSource(QUrl::fromLocalFile(path + file));
appview->setResizeMode(QDeclarativeView::SizeRootObjectToView);
appview->setAttribute(Qt::WA_OpaquePaintEvent);
appview->setAttribute(Qt::WA_NoSystemBackground);
appview->viewport()->setAttribute(Qt::WA_OpaquePaintEvent);
appview->viewport()->setAttribute(Qt::WA_NoSystemBackground);
appview->showFullScreen();
binding_map["question_txt"] = QVariant(QString("overwritten 5 * 5 ="));
return myapp->exec();
}
</code>
I need to let C++ print text in the QML interface (the question)
and C++ has to obtain the
answer the user has answered in the QML interface (TextField
Silica component). That's basically
the needed communication between C++ and QML.
So I thought that I'd create a QDeclarativePropertyMap in C++.
This propertymap will contain the question.
My program has a while loop that asks the user new questions each
time the loop runs(the logic code can be found here
<https://bitbucket.org/Superpelican/clamshell_cli>,
but it hasn't been adjusted for use with a GUI, it's currently a
CLI application). So I need to constantly update the QML UI from C++
while the programs running, after I've setup the QDeclarativeView etc.
However I noticed that if you change a value in the propertymap
after initializing and showing the QDeclarativeView, the UI won't
be updated!
I thought the QDeclarativePropertyMap was dynamic!
http://qt-project.org/doc/qt-4.8/qdeclarativepropertymap.html#details:
"The binding is dynamic - whenever a key's value is updated,
anything bound to that key will be updated as well."
Kind Regards,
Superpelican
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