[Solved] Sliding Bar Graph

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Thanks ZapB.

I had a look into the simple progress bar QML. I will go ahead and see if I can add a different property to it.

I have another question:

I need to interface qt with the back end C application to obtain real time data using any of the process that you suggested(QProcess etc.,) above.
If I do it, is it possible to integrate Qt with the QML user interface and manipulate the properties of the objects(sliding bar graph) on the QML user interface?

Thanks for your assistance.

Apologies if I sound very naive.

Balaji

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Yes this is possible. Some tags to search for on QtDevNet are things like "qml c++ integration".

The basic principal is that you create a C++ class that inherits QObject and in this class you declare some properties using Q_DECLARE_PROPERTY macro. These properties represent the quantities that you wish to display in your QML gui. You then expose your C++ object(s) to the QDeclarativeConext object using the setContextProperty() function.

In you QML gui you can then bind properties of your QML items to the properties of your C++ object(s).

It is up to you how to factor your C++ object(s) and their properties to map onto your data.

This kind of design leads to a nice separation of concerns. You will have a component that retrieves the data from your existing C application somehow and populates the properties of your C++ QObject subclasses. Then you have your GUI in QML which is only dependent upon the names and types of object and properties exposed to it form the C++ side. So you can very easily swap out the GUI for a new one without touching the backend code if needed.

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ZapB
I will try it out and let you know. All of you r suggestions were very useful. Thanks for you valuable guidance.

Bsbala

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Hi,

I am still trying and I will let you know once I am done. It moving at a pretty slow rate :-)

Balaji

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Hi,

I tried your progress bar graph illustration it was working fine, when I used it with a single value change from the C++ program.

I am trying to change the graph value with the values from the external "C" program using Qprocess. I am not sure on how to proceed with the program structure. Can you please suggest me. Should the QProcess be a part of some class along with the QML?.

Thanks for your assistance.

Balaji

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ZapB,

I was able to connect the QML and was able to connect to the output of the C program(the program just outputs from 1 to 100) using QProcess. However the value from the standard output seems to be a stream and the toInt function does not recognize it and returns a value of '0' and the Graph displays with no fill.

Thanks a lot for providing your valuable assistance.
BsBala

This is the coding for the Qprocess.

@#include <QApplication>
#include <QDeclarativeView>
#include <QDeclarativeContext>
#include <QDeclarativeProperty>
#include <QGraphicsObject>
#include <QDebug>
#include<QObject>
#include<QProcess>

#include "processconnector.h"
#include "slidinggraph.h"

ProcessConnector::ProcessConnector(QObject *parent){
process = new QProcess(this);
process->setReadChannel(QProcess::StandardOutput);
connect(process, SIGNAL(readyReadStandardOutput()),this, SLOT(disp()));
process->start("./op");

}

void ProcessConnector::disp()
{
while( 1 ){
QString t = process->readLine();
if( t.isEmpty() ) break;
qDebug() << "got output" << t.toInt();
emit valueChanged(t.toInt());

}

}
@

This is the coding for the QML object.

@#include <QApplication>
#include <QDeclarativeView>
#include <QDeclarativeContext>
#include <QDeclarativeProperty>
#include <QGraphicsObject>
#include <QDebug>
#include<QObject>
#include<QProcess>
#include<slidinggraph.h>

SlidingGraph::SlidingGraph(QObject *parent){

view.setSource(QUrl::fromLocalFile("qml/QMLconnector/main.qml"));
QObject object = view.rootObject();
progressbar = object->findChild<QObject>("bar");
view.show();
}

void SlidingGraph::setvalue(int value){
if(progressbar)
progressbar->setProperty("value",value);

}
@

This is the main.cpp

@#include <QtGui/QApplication>
#include "qmlapplicationviewer.h"
#include "processconnector.h"
#include "slidinggraph.h"
#include <QObject>

int main(int argc, char *argv[])
{
QApplication app(argc, argv);

ProcessConnector *Pc = new ProcessConnector();
SlidingGraph *sl = new SlidingGraph();
QObject::connect(Pc,SIGNAL(valueChanged(int)),sl,SLOT(setvalue(int)));
sl->view.show();
return app.exec&#40;&#41;;

}
@

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I was able to solve the problem. Zap B thanks for helping me out on this.

BSBALA

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Ah glad you got this sorted. Sorry I've not had time to look at it. Things have been a bit hectic here the last couple of weeks. What was the problem and solution in the end?

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Hi ZapB,

Nice to hear from you. Actually I had my friend code the C part which had some mistakes. He corrected it . I had good sliding graph. Thanks for your help.I got a good idea for working with QML. I have some other questions about QML multiple screens and how to make underlying Qt C++ layer to handle it. I will post it in a new thread. Please help me out if you find some time.

I appreciate all your help, guidance and time you have taken to reply my questions.

Balaji

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No worries. I'll keep an eye out for it but I'll be away on holidays next week. I'm sure somebody else will jump in to help you though.

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Thanks a lot ZapB.