SDK/Docs/1.1/Creating Hello World

Revision as of 11:26, 29 October 2010

Note: This page is work-in-progress (26 Oct 2010).

This page explains how to create a Hello World application with Qt Creator and run it on a MeeGo device (real or emulated).

Prerequisites

• You have set up MeeGo SDK environment on Linux
• You have installed the MeeGo image and configured the device access in Qt Creator.

Creating a Hello World

To create a project:

1. In Qt Creator, select File > New File or Project.
2. Select Mobile Qt Application and click Choose....

   

   Creating your project

3. Name your project, select where you want to save it, and click Next.

   Note: Make sure that the path to the location does not contain spaces.

   

   Naming your project

4. Select MeeGo target and click Next.

   

   Selecting the MeeGo target

5. Name the files that will be automatically created for your project.

   

   Naming classes for your project

6. If you want to add the project to version control, do so. Otherwise click Finish.

   

   Adding your project to version control

Your project has now been created.

To create a Hello World application:

For more information on the Hello World created here, see the Qt Mobility Quickstart Example.

1. In Qt Creator, select Edit mode.

2. To view your project files, open Forms, Headers, and Sources folders in Projects sidebar.

3. To create an application that uses the QSystemInfo headers to print out the system's current country code, replace the existing example code in your main.cpp file with the following example code:

#include <QApplication>
#include <QLabel>
#include <QSystemInfo>
using namespace QtMobility;

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QSystemInfo s;
    QLabel *label = new QLabel(QObject::tr("hello ").append(s.currentCountryCode()));
    label->show();
    label->resize(100,30);
    return app.exec();
}

4. Replace the corresponding lines in your .pro file with the following System Information API declaration:

CONFIG += mobility
MOBILITY += systeminfo

Do not remove the existing code in the file.

5. In the File menu, select Save All.

Your application is now ready to be configured for building.

To configure your Hello World for building:

1. Switch to Projects mode.
2. Click Build Settings.
3. On Edit build configuration: line, select Add > Using Qt version "MeeGo sysroot".
4. Change Debug into MeeGo sysroot Release.

   

   Configuring build settings in Qt Creator

   Your Hello World is now ready to be configured for running in QEMU or your device.

Packaging the Hello World

If you run your Hello World application, an .rpm package is created automatically.

If you want to create a package of your Hello World application without running it, click Build All or select Build > Build Project "<project name>".

Compile Output view shows the message "Package created." and an .rpm package file (<project name>-<project version>-<release version>.<device architecture>.rpm) has been created in the build-specific project subdirectory ("<project name>-build-meego").

Configuring device access in Qt Creator

The process is slightly different, depending on whether you are deploying to a real device or an emulated one.

However, in both cases, the mode of access is the same: Qt Creator will deploy and install an RPM on the device, then run its executable.

• N900
• Netbook
• QEMU image

Running the Hello World

To run your Hello World on your device:

1. Switch to Projects mode.
2. Click Run Settings.
3. In Device configuration drop-down menu, select the device configuration you created when configuring device access.

   

4. Click .

   Your Hello World runs on your device.

Here's an example of the application running on a netbook:

Debugging the project

Prepare the host

You will need gdb to be installed on the host before you can do any debugging with Qt Creator. On Linux, use the package manager to install it; for example, on Fedora:

sudo yum install gdb

Configure the Qt Creator project for debugging

First, ensure that debugging is enabled for the version of Qt in use:

1. Click on the Projects button in the left-hand panel.
2. Under General, click on the Manage button next to Qt Version.
3. Select the Qt version you are using: use the MeeGo Qt version for your particular target (in this case, MeeGo sysroot).
4. Click on the Rebuild button next to Debugging helpers (near the bottom of the dialog box). This builds the debugging helper for this version of Qt. You should see a green tick under the Debugging column for that Qt version.

Set a breakpoint

Next, you need something to debug. For example, add a Push Button to the form (defined in mainwindow.ui):

Then add a click handler for it, so that when the button is clicked, a message string is assigned into a variable then output to the console. The code looks like this:

/* file: Sources/main.cpp */
#include <QtGui/QApplication>
#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

/* file: Headers/mainwindow.h */
#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Ui::MainWindow *ui;

// our new handler
private slots:
    void on_pushButton_clicked();
};

#endif // MAINWINDOW_H

/* file: Sources/mainwindow.cpp */
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
#include <QString>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_pushButton_clicked()
{
    QString message;
    message = "I have been well and truly clicked";
    qDebug() << message;
}

Most of this is boilerplate generated the project was started, but the MainWindow::on_pushButton_clicked method is new. Notice how it also needs to be defined as a private slot in the header file.

Add a breakpoint next to the line where you want the debugger to break by clicking in the editor margin. It looks like this:

(See the red circle on line 22 after message is initialized.)

To put Qt Creator into debug mode, click on Debug/the bug icon in the left-hand toolbar. This adds some extra panels to the window which are used to show the stack, watch expressions etc.

Next, you need to change the configuration, so that Qt with debugging enabled is used to run the project.

1. In the left-hand panel, click on Projects.
2. Under Build Settings, select Debug from the drop-down box next to Edit build configuration.
3. From the Build menu, select Rebuild all. This recompiles the project using the debug-enabled Qt.

Debug the application on the device

To run the application in debug mode, click on the green arrow with a bug overlaid on it (bottom left). This deploys the application to the remote device and starts it, as above; however, it also enables you to debug the remote application inside Qt Creator.

Now, click on the Click me! button in the application running on the device. The program should pause at the breakpoint. Switch back to Qt Creator and look at the debug panels:

The application should pause at the breakpoint; and in Qt Creator, the message variable should then be visible in the Locals and Watchers tab, set to "I have been well and truly clicked".

For more information about using Qt Creator in debug mode, see http://doc.qt.nokia.com/qtcreator-snapshot/creator-debugging.html.