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Thread: "QPixmap: Must construct a QGuiApplication before a QPixmap" Debug Error!

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  1. #1
    Join Date
    Dec 2018
    Posts
    7
    Qt products
    Qt5
    Platforms
    Windows

    Default "QPixmap: Must construct a QGuiApplication before a QPixmap" Debug Error!

    While running our app developed on Windows 10 and closing the gui window with the "X" button we get a Microsoft Visual C++ Runtime Library Error (see attachment).
    When running in debug mode an exception is triggered in the QApplication::exec() method.

    MicrosoftError.PNG

    This is our main function:

    Qt Code:
    1. int main(int argc, char *argv[])
    2. {
    3. QApplication app(argc, argv);
    4. GeDetektEventFilter filter;
    5. app.installNativeEventFilter(&filter);
    6.  
    7. std::unique_ptr<Sentinel>& sentinel = Sentinel::getInstance();
    8. sentinel->connectThreads();
    9. sentinel->createAppFiles();
    10. sentinel->startQmlEngine();
    11.  
    12. sentinel->startHardware();
    13.  
    14. manager::connections::connectAll();
    15.  
    16. //Uncomment this to deactivate tests (not recommended)
    17. ::testing::InitGoogleTest(&argc, argv);
    18. RUN_ALL_TESTS();
    19.  
    20. return qApp->exec();
    21. }
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    Our Gui is created with QtQuick and qml.

    Qt Code:
    1. import QtQuick 2.2
    2. import QtQuick.Window 2.12
    3. import QtQuick.Controls 1.4
    4. import QtQuick.Layouts 1.12
    5.  
    6. import DisplayInformation 1.0
    7.  
    8. Window
    9. {
    10. id: mainWindow
    11.  
    12. visible: true
    13. width: displayInformation.WINDOW_SIZE.width + displayInformation.SIDE_BAR_WIDTH
    14. height: displayInformation.WINDOW_SIZE.height
    15. title: qsTr("Sentinel")
    16.  
    17. maximumHeight: height
    18. maximumWidth: width
    19. minimumHeight: height
    20. minimumWidth: width
    21.  
    22. //Old Qt Bug Displays error here although functional
    23. onClosing:
    24. {
    25. sentinel.stopComClient();
    26. }
    27.  
    28. Rectangle
    29. {
    30. id: mainArea
    31. Keys.onPressed:
    32. {
    33. if (event.key === Qt.Key_F9)
    34. {
    35. sidebarLoader.source = ""
    36. qmlEngine.clearCache()
    37. sidebarLoader.source = "Sidebar.qml"
    38.  
    39. imageDisplayLoader.source = ""
    40. qmlEngine.clearCache()
    41. imageDisplayLoader.source = "ImageDisplay.qml"
    42.  
    43. if (mainArea.logOpen === true)
    44. {
    45. mainArea.logWindow.close()
    46. mainArea.logComponent.source = ""
    47. qmlEngine.clearCache()
    48. mainArea.logComponent.source = "LogWindow.qml"
    49. }
    50.  
    51. console.log("Sources Reloaded");
    52.  
    53. event.accepted = true;
    54. }
    55.  
    56. if (event.key === Qt.Key_L && logOpen === false)
    57. {
    58. sentinel.startHardware()
    59.  
    60. console.log("Log Window")
    61. logComponent = Qt.createComponent("LogWindow.qml")
    62. logWindow = logComponent.createObject(mainWindow)
    63.  
    64. logWindow.show()
    65. logOpen = true
    66. }
    67. }
    68.  
    69. Connections
    70. {
    71. target: mainArea.logWindow
    72. onClosing:
    73. {
    74. console.log("Log Window closed")
    75. mainArea.logOpen = false
    76. }
    77. }
    78.  
    79. property bool scanAvailable: false
    80. property bool scanStopped: true
    81. property bool logOpen: false
    82. property Window logWindow
    83. property Component logComponent
    84. }
    85.  
    86. RowLayout
    87. {
    88. id: rowLayout
    89. anchors.fill: parent
    90.  
    91. Loader
    92. {
    93. id: imageDisplayLoader
    94. source: "ImageDisplay.qml"
    95. }
    96.  
    97. Loader
    98. {
    99. id: sidebarLoader
    100. Layout.fillHeight: true
    101. Layout.fillWidth: true
    102. source: "Sidebar.qml"
    103. }
    104. }
    105. }
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    The qml files are loaded in following function over an environment variable:

    Qt Code:
    1. void Sentinel::startQmlEngine()
    2. {
    3. qmlRegisterType<gui::DisplayInformation>("DisplayInformation", 1, 0, "DisplayInformation");
    4. qmlRegisterType<gui::ImageItem>("ImageItem",1,0,"ImageItem");
    5. qmlRegisterType<gui::ImageProvider>("ImageProvider", 1, 0, "ImageProvider");
    6.  
    7. m_qmlEngine.rootContext()->setContextProperty("displayInformation",
    8. &m_imageProvider.getDisplayInformation());
    9.  
    10. m_qmlEngine.rootContext()->setContextProperty("sentinel", this);
    11. m_qmlEngine.rootContext()->setContextProperty("imageProvider", &m_imageProvider);
    12. m_qmlEngine.rootContext()->setContextProperty("scanArea", modules::ScanArea::getInstance().get());
    13. m_qmlEngine.rootContext()->setContextProperty("comClient", modules::ComClient::getInstance().get());
    14. m_qmlEngine.rootContext()->setContextProperty("ptu", modules::PtuControl::getInstance().get());
    15. m_qmlEngine.rootContext()->setContextProperty("logOutput", helpers::LogOutput::getInstance().get());
    16. m_qmlEngine.rootContext()->setContextProperty("qmlEngine", &m_qmlEngine);
    17.  
    18. m_qmlEngine.load(qEnvironmentVariable("MAIN_QML"));
    19. assert(!m_qmlEngine.rootObjects().isEmpty());
    20.  
    21. //These are the connections interfacing module state to gui (image processing methods and qml)
    22. using namespace modules;
    23.  
    24. QObject::connect(&m_imageProvider,
    25. &gui::ImageProvider::backgroundChanged,
    26. this, &Sentinel::updateBackgroundS);
    27.  
    28. QObject::connect(ComClient::getInstance().get(),
    29. &ComClient::compoundsNameAndStateChanged,
    30. this, &Sentinel::updateCompoundsS);
    31.  
    32. QObject::connect(GigECamera::getInstance().get(),
    33. &GigECamera::newFrameAvailable,
    34. &m_imageProvider,
    35. &gui::ImageProvider::updateBackgroundImage);
    36.  
    37. QObject::connect(ToxelBufferExtractor::getInstance().get(),
    38. &ToxelBufferExtractor::updateToxelPixel,
    39. &m_imageProvider,
    40. &gui::ImageProvider::paintNewOverlayCircle);
    41. }
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    I've researched for quite a bit to find a solution for this and have seen there were some reported bugs refering to this error. However, I am not sure if and when these bugs have been fixed or even apply to our problem.
    There might also be something missing in the way we create and quit the app as this is a very general application scenario for a Qt app and quite a disturbing behaviour.

    Very grateful for any suggestions.

  2. #2
    Join Date
    Jan 2006
    Location
    Graz, Austria
    Posts
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    Thanks
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    Qt products
    Qt3 Qt4 Qt5
    Platforms
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    Default Re: "QPixmap: Must construct a QGuiApplication before a QPixmap" Debug Error!

    The error usually only happens at startup but you are saying it happens after the application has run successfully and you are closing its window, correct?

    Cheers,
    _

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