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• Should I base my Embedded Linux product on Qt?

  - by Udi

  My company is developing a medical product. One of the components is a pda-like platform that will run embedded linux. We were considering Qt as the UI framework but found out that Qt is a lot more than that (we are not familiar with Qt). In general, the device needs to do the following: 1. Receive measurements over USB HID from another device (USB HID is used for convenience). 2. Process the measurements. 3. Store them in a database. 4. Interact with the user using the device's touch screen lcd. 5. Communicate (wi-fi, tcp-ip) with a central management station that collects the data and configures the device. 6. Include a web server to allow accessing the device via a browser. We intend to program in C++. My questions are: 1. Is that a good choice for such a device? 2. Assuming we choose Qt, how do we build our product? - Do we use Qt just as a GUI framework and write the application code in a separate process (passing messages between Qt and the application process)? - Do we write the entire application inside Qt, using all of the services the tool has to offer? - Another approach?

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• Proper use of Q_OBJECT?

  - by Jen

  If I derive my class from QObject (or a subclass), the Qt documentation says that I have to put the Q_OBJECT macro into my class declaration. It also ways I need to "run the meta-object compiler" for my class. I have no idea how to do this. Is this something I need to add to the .pro file? Do I need to edit the makefile? This seems overly complicated for a simple derived class. I'm using Qt Creator.

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• Why can't I set a layout for a page in a QStackedWidget in designer?

  - by cppguy

  Steps to reproduce in designer for Qt 4.8.0 I create a new dialog form in Qt Designer I add a QStackedWidget to the dialog I set the layout of the dialog to make the stacked layout size with the dialog I add a few controls to page one in the stacked widget I select the first page in the stacked widget in the right hand tree view of controls The icon next to that page (which is a QWidget) shows the page is missing a layout When I click one of the layout buttons above, it doesn't change the layout of the page QWidget, it changes the layout of the dialog even though I had explicitly selected the page. Is this a bug in designer? Am I missing something? I really don't want to add the layouts programatically as that prevents me from being able to layout the pages in designer in the same .ui file

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• QT's QGraphicsview clickable icon on screen

  - by goodwince

  I'm working on a project with QT and am trying to draw icons from a database. I have auxiliary information in the table that I would like to display if the user chooses to see it (i.e. the x,y of the icon and some other options from database). I am debating on would it be better to go through and just redraw all the icons with this information added, or do some sort of looping through the icons and setting some value to true to display the information. Thanks in advance.

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• calling Qt's QGraphicsView::setViewport with a custom QGLWidget

  - by mos

  I've derived from QGLWidget before, like so: class MyGLWidget : public QGLWidget { public: // stuff... virtual void initializeGL() { /* my custom OpenGL initialization routine */ } // more stuff... }; However, I find that if I try to initialize a QGraphicsView with my custom QGLWidget as the viewport, initializeGL doesn't get called (setting a breakpoint within the Qt library, neither does QGLWidget::initializeGL() when created plain). // initializeGL, resizeGL, paintGL not called ui.graphicsView->setViewport(new MyGLWidget(QGLFormat(QGL::DoubleBuffer))); // initializeGL, resizeGL, paintGL *still* not called ui.graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::DoubleBuffer))); Where is the correct location to place the code that currently resides in MyGLWidget::initializeGL()?

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• Importing .dll into Qt

  - by Bad Man

  I want to bring a .dll dependency into my Qt project. So I added this to my .pro file: win32 { LIBS += C:\lib\dependency.lib LIBS += C:\lib\dependency.dll } And then (I don't know if this is the right syntax or not) #include <windows.h> Q_DECL_IMPORT int WINAPI DoSomething(); btw the .dll looks something like this: #include <windows.h> BOOL APIENTRY DllMain(HANDLE hModule, DWORD ul_reason_for_call, LPVOID lpReserved) { return TRUE; } extern "C" { int WINAPI DoSomething() { return -1; } }; Getting error: unresolved symbol? Note: I'm not experienced with .dll's outside of .NET's ez pz assembly architechture, definitely a n00b.

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• click feature in Qt

  - by Solitaire

  Hi, I just want to clarify, weather the feature is present or not in Qt. The scenario is like this, I have a list view with items, I want to place the icon to the listview when the item is selected. The selection I mean is, first time when I click item should be selected, next time if I click the same item then it should be selected. Please note It is not the double click. So is there any feature which handles this feature by default, any property or flag which I need to set to listview to behave like this or manual implementation Is required for this.

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• qt/wxwidgets third party components?

  - by tkd

  I'm used to working in a Delphi and C# environment which seem to have a rich set of third party components available. I'm currently wanting to do cross-platform programming in C++ using either qt or wxwidgets. Is there a large market for third party components? I was looking at sourceforge and that doesn't seem to show much that is useful (how the hell do you find out what components or features are in a project without downloading the source?). I'm thinking carousel/coverflow components, rich datagrids (like the sort DevExpress provide). Or is this, write your own territory?

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• QT: Scroll widget that renders directly to the DC

  - by shoosh

  I'm trying to create a widget which paints directly to the windows Device Context by calling getDC() and painting an HBITMAP to it. The widget I'm painting resides inside a scroll widget. I've implemented the paintEvent() and it does seem to paint but immediatly after painting the widget gets painted over again with a blank gray color. I've tried setting WA_PaintOnScreen and Qt::WA_NoSystemBackground but none of those help. In theory this should be possible since this is basically how the GLWidget works. What am I missing?

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• Get http status in Qt WebKit

  - by RR

  Hello all: What I would like to implement is 1 Using Qt's WebView(part of QtWebKit) to access some page. 2 Show specified html page if got HTTP 4xx, 5xx status (Ex HTTP 404, 500). 3 Also shows specified page when network connection is unavailable. For now, I had only done job 1... In job 2, how did I get http status from WebView ? In job 3, I'm looking about QUrl APIs now. Anyone have idea or expreience yet ?

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• Qt not displaying PNG images on Linux

  - by ereOn

  Hi, I have a software written using Qt which is meant to work on both Windows and Linux. I use PNG images as icons for my QActions, embedded in a resource. I have the following tree directory: / resources/ icons.qrc image.png Here is the content of icons.qrc: <RCC> <qresource prefix="/resources" lang="fr"> <file alias="image.png">image.png</file> </qresource> </RCC> I declare my QIcon like that: QIcon(":/resources/image.png") Under Windows, it works well but on Linux (I only tried on Ubuntu 10.4 so far), the images aren't displayed. Is there anything special I have to do for this to work ? Is this a configuration problem ? Thank you.

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• How do I copy object in Qt?

  - by Martin

  I'm using Qt and have some real basic problems. I have created my own widget MyTest that have a variable obj. I need to set this variable obj from an object outside of the widget so that the variable is copied not just a pointer to another object. I get an error message and can't figure out how to do this basic stuff. This is the code I'm using: MyTest.h: class MyTest : public QWidget { Q_OBJECT public: void setObj(QObject &inobj); QObject obj; .... } MyTest.cpp: void MyTest::setObj(QObject &inobj) { obj = inobj; //HERE I get the error message: "illegal access from 'QObject' to protected/private member 'QObject::operator=(const QObject &)'" } main.cpp: int main(int argc, char *argv[]) { QApplication a(argc, argv); QObject *ob = new QObject(); MyTest w; w.setObj(*ob); } Thanks for your help!

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• Qt Graphics Scene mouse event propagation

  - by Olorin

  hello i'm learning qt and i'm doing the folowing to add some widgets to a graphics scene void MainWindow::addWidgets(QList<QWidget *> &list, int code) { if(code == CODE_INFO) { QWidget *layoutWidget = new QWidget(); QVBoxLayout *layout = new QVBoxLayout(); foreach(QWidget *w, list) { layout->addWidget(w); this->connect(((ProductInfo*)w), SIGNAL(productClicked()), this, SLOT(getProductDetails())); } layoutWidget->setLayout(layout); this->scene->addWidget(layoutWidget); } } my ProductInfo class processes mouse release and emits a signal void ProductInfo::mouseReleaseEvent(QMouseEvent *e) { QWidget::mouseReleaseEvent(e); emit productClicked(); } the problem is after adding the widgets to the scene they no longer get the mouse release event and don't emit productClicked signal but if i add them to the main window(not to the scene) they work as expected. What am i doing wrong?

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• Memory management in Qt?

  - by Martin

  I'm quite new to Qt and am wondering on some basic stuff with memory management and the life of objects. When do I need to delete / destroy my objects? Is any of this handled automatically? In the example below, which of the objects I create do I need to delete? What happens to the instance variable myOtherClass when myClass is destroyed? What happens if I don't delete / destroy my objects at all, will that be a problem to memory? in MyClass.h: class MyClass { public: MyClass(); ~MyClass(); MyOtherClass *myOtherClass; }; in MyClass.cpp: MyClass::MyClass() { myOtherClass = new MyOtherClass(); MyOtherClass myOtherClass2; QString myString = "Hello"; } As you can see this is quite newbie-easy stuff but where can I learn about this in an easy way? Thanks really much

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• Overlapping labels in Qt fridge magnets example

  - by bullettime

  I want to modify the fridge magnets example provided with Qt in a way that when I drag a label and drop it over another, it will push the label beneath the dragged label to the side, so they will never overlap one another. I've seen how collision is detected in the colliding mice example, where it uses a QGraphicsScene to draw the QGraphicsItem mice on, and scene()-collidingItems(this) to see which mice are colliding. The problem is that the fridge magnets example uses a class that inherits QWidget in place of QGraphicsScene, so there's no collidingItems() method to check when we have a collision. How do I go about doing that?

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• Determine signals connected to a given slot in Qt

  - by Cody Brocious

  I've injected myself into a Qt application, and I'm attempting to figure out what signals a given slot is connected to, but can't find any information on doing this. Is there a mechanism for doing this out of the box? If so, is this exposed to QtScript? (If not, I can wrap it easily enough.) If there is no such mechanism, what would be the best way to add it? I cannot manipulate the existing application outside of simple hooking, but I could hook QObject::connect and store the connections myself, just not sure if that's the best way to go about it.

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• Function matching in Qt

  - by Alexander

  Hello, I have some trouble with Qt. I have a class 'Core' class Core { public: static QString get_file_content(QString filename); static void setMainwindow(MainWindow *w); private: static MainWindow *main_window; }; and class 'MainWindow' in namespace Ui: namespace Ui { class MainWindow; } class MainWindow : public QMainWindow { Q_OBJECT public: MainWindow(QWidget *parent = 0); ~MainWindow(); private: Ui::MainWindow *ui; }; In MainWindow constructor I make MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow) { ui->setupUi(this); Core::setMainwindow(this); } and gets error mainwindow.cpp:8: error: no matching function for call to 'Core::setMainwindow(MainWindow* const)' Of cource, i include core.h with declaration of 'Core' class. That's occurs only on setMainwindow method. So the questions is - why Core class method setMainwindow() is invisible in MainWindow class?

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• how to implement OOP using QT

  - by kaycee

  hi, this is a simple OOP QT question. my app consists of main window (QMainWindow) and a table (QTableWidget). in the main window i have arguments and variables which i would like to pass to the table class, and to access methods in main widnow class from the table class, how should i do it ? mainwindow.h class MainWindow : public QMainWindow { Q_OBJECT private: int a; int b; Spreadsheet *spreadsheet; public: void set_a(int); void set_b(int); spreadsheet.h class Spreadsheet : public QTableWidget { Q_OBJECT public: Spreadsheet(QWidget *parent = 0); atm i define Spreadsheet like this: spreadsheet = new Spreadsheet(this); and i'd like to access set_a() from spreadsheet.cpp...

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• Block All Keyboard Input in a Linux Application (Using Qt or Mono)

  - by Evans

  Hi, I'm working on a online quiz client where we use a dedicated custom-made linux distro which contains only the quiz client software along with text editors and other utility software. When the user has started the quiz, I want to prevent him/her from minimizing the window/closing it/switching to the desktop or other windows. The quizzes can be attempted using only the mouse, so I need the keyboard to be completed disabled for the period of the quiz. How could I do this, using Qt or Mono? I'm ready to use any low-level libraries/drivers, if required. Thanks Evans

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• Architectural decision : QT or Eclipse Platform ?

  - by umanga

  We are in the process of designing a tool to be used with HDEM(High Definition Electron Microscope).We get stacks of 2D images from HDEM and first step is 'detecting borders' on the sections.After detecting edges of 2D slices ,next step is construct the 3D model using these 2D slices. This 'border detecting' algorithm(s) is/are implemented by one of professor and he has used and suggests to use C.(to gain high performance and probably will parallelise in future) We have to develop comprehensive UI ,3D viewer ,2D editor...etc and use this algorithm. Application should support usual features like project save/open.Undo,Redo...etc Our technology decisions are: A) Build entire platform from the scratch using QT. B) Use Eclipse Platform Our concerns are, if we choose A) we can easily integrate the 'border detecting' algorithm(s) because the development environment is C/C++ But we have to implement the basic features from the scratch. If we choose B) we get basic features from the Eclipse platform , but integrating C libraries going to be a tedious task. Any suggestions on this?

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• How to create a new File in Qt

  - by GG

  Hello friends, I am a Qt beginner and just got stuck with the problem. I am looking for a file SomePath/NewDirectoryA/NewFile.kml ( NewFile.kml will be the only file in NewDirectoryA, having this directory just to maintain semantics in the project ). If SomePath/NewDirectoryA/NewFile.kml exists then I will use it in my code and If it doesn't exist then I have to create it. If this File doesn't exist then this directory also doesn't exist in SomePath. So If only I have to create a file I can use QFile and open it in ReadWrite or WriteOnly mode. But the problem is I have to create the file with the directory itself. I tried with QFile with file name SomePath/NewDirectoryA/NewFile.kml but it didn't worked. Please suggest me a way in which I can create a new file( NewFile.kml ) in a new directory( NewDirectorA ) at a given location( SomePath ).

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• Can Qt's QWebView display programatically generated XML?

  - by Dan Ellis

  Using Qt 4.6, I can dynamically add to an HTML page like this: ui->webView->page()->mainFrame()->documentElement().findFirst("body").appendInside("<i>some text</i>\n"); However, if I QWebView::load() an XML file, it displays it with the correct CSS styling (from an processing instruction), but doesn't show any changes when I do something like: ui->webView->page()->mainFrame()->documentElement().findFirst("lines").appendInside("<line>hello</line>\n"); Why is it treating them differently, and is there a way to modify an XML document in the same way I can an HTML one?

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• Qt QTextEdit Qt4.2 Valid HTML String

  - by Matthew Hoggan

  I am trying to generate the correct HTML to render to a QTextEdit Using Qt 4.2 on RHEL 5.3. So far my algorithm generates the following html. I am not an expert web developer, but to me this string seems valid. 319:14:27:22: <font color="rgb(255,0,0)" bgcolor="rgb(255,0,0)">Message</font><br> What needs to change to get the colours to render. Currently it just renders as black text on a white background.

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• Qt for Symbian - Detecting touch/non-touch devices...

  - by Nikos

  I'm porting a game for Symbian which supports both a touch & non-touch UI. I need to be able to tell if the device has a touch screen on start-up so I can enable the appropriate mode. After googling for hours and going though the Qt Docs I found QSysInfo but this merely provides the version of the Symbian device. Is there a way to get the actual capabilities of the device? There must be a way to tell if the device has a touch screen...! I'm using the latest QtCreator with the NokiaSDK. Thank you in advance, Nikos.

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• using sqlite database with qt

  - by Lakshan Perera

  here is my code, it dont seems enything wrong, QSqlDatabase db=QSqlDatabase::addDatabase("QSQLITE"); db.setDatabaseName("thedata.sqlite"); db.open(); QSqlQuery quary; quary.prepare("SELECT lastname FROM people where firstname='?' "); quary.bindValue(0,lineEdit->text()); bool x=quary.exec(); if(x){ //...... } else { QSqlError err; err=quary.lastError(); QMessageBox::about(this,"error",err.text() ); } when the program is working always it gives the error parameter count mismatch im using qt 4.8 and its own headers for using sqlite. I would be very thankful for eny advice, though I searched in google i see many posts in this issue but nothing helped me. thank you.

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