Interview Questions.

Top 100+ Qt Qml Interview Questions And Answers

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Top 100+ Qt Qml Interview Questions And Answers

Question 1. What Is Qt?

Answer :

Qt is a cross-platform utility framework this is broadly used for growing software software program that may be run on various software and hardware structures with very little alternate in the underlying codebase,

Question 2. What Is A Framework?

Answer :

framework  is an crucial helping structure of a building, automobile, or object.

Frameworks are a unique case of software libraries in that they are reusable abstractions of cod wrapped in a nicely-defined Application programming interface (API), that is overridden by person.
Frameworks  is an abstraction in which not unusual code presenting conventional capability can be selectively overridden or specialised by using person code offering particular functionality
Framework->uses your code.
Library->you operate library code.

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Question three. What Is Qmake?

Answer :

qmake is a utility that automates the era of Makefiles.

Makefiles are used by the program make to build executable applications from supply code; therefore qmake is a make-makefile tool, or makemake for quick.

QMake does no longer call g++/gcc directly. Instead, qmake creates local make files to your cutting-edge platform. Under linux it creates wellknown GNU make documents, beneath home windows it could generate visible studio make documents, underneath Mac OS X it can generate XCode project files. You then invoke your local construct device (both GNU make, or MS NMake, or xcodebuild or some thing), a good way to call your local compiler (g++/gcc or something).

Question 4. What Is Qt And Qml?

Answer :

Qt is a pass-platform software framework.

QML is the name of the language (just like C++, that's some other language...)

QML stands for Qt Meta Language or Qt Modelling Language is a person interface markup language.

QtQuick is a toolkit for QML, permitting to expand graphical interface in QML language (there are other toolkits for QML, some are graphical like Sailfish Silica or BlackBerry Cascade, and a few are non-graphical like QBS which is a substitute for QMake/CMake/make...)

QtQuick 1.X changed into Qt4.X-based and used the QPainter/QGraphicsView API to attract the scene. QtQuick 2.X changed into introduced with Qt5.0, primarily based on Scene Graph, an OpenGLES2 abstraction layer, pretty optimized.

With Qt5.1, Scene Graph become more suitable to apply multithreading (QtQuick 2.1) With Qt5.2,

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Question five. What Is Qt's Meta Object System?

Answer :

Qt's meta-object gadget affords the alerts and slots mechanism for inter-object communique, run-time type information, and the dynamic property gadget.

The meta-item system is based on three things:

The QObject magnificence presents a base magnificence for items that may take advantage of the meta-object gadget.
The Q_OBJECT macro within the personal phase of the class declaration is used to permit meta-object features, which includes dynamic houses, indicators, and slots.
The Meta-Object Compiler (moc) resources every QObject subclass with the important code to put into effect meta-item functions.
The moc tool reads a C++ source document. If it unearths one or greater elegance declarations that include the Q_OBJECTmacro, it produces any other C++ supply file which incorporates the meta-item code for each of these instructions.

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Question 6. Can Moc File Handle All Class Type?

Answer :

No, elegance template cannot have sign slot. Can not be treated by using moc.

Question 7. What Are Limitations Of Moc?

Answer :

moc does not cope with all of C++.E.G.
The fundamental trouble is that elegance templates can't have indicators or slots.
Function Pointers Cannot Be Signal or Slot Parameters
Type Macros Cannot Be Used for Signal and Slot Parameters
Nested Classes Cannot Have Signals or Slots
Signal/Slot return kinds can't be references
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Question 8. What Is Qvariant?

Answer :

QVariant is a field of variables. It can save variables of various sorts. Similar in some manner to void*. But it affords You records approximately the stored type.

It can be used as an example to go back specific types of values from a feature.

Question 9. What Is Qt Creator?

Answer :

Qt Creator presents a pass-platform, whole incorporated development surroundings (IDE) for software developers to create programs for a couple of laptop, embedded, and cell device platforms, which include Android and iOS. It is available for Linux, mac-OS and Windows operating systems.

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Question 10. What Is Qt Widgets?

Answer :

Widgets are the fundamental building blocks for graphical user interface (GUI) programs constructed with Qt. Each GUI thing (e.G. Buttons, labels, textual content editor) is a widget that is positioned somewhere inside a user interface window, or is displayed as an impartial window. Each kind of widge is furnished by way of a subclass of QWidget, that is itself a subclass of QObject.

QWidget isn't an abstract magnificence. It can be used as a box for different widgets, and it may be subclassed with minimal attempt to create new, custom widgets. QWidget is frequently used to create a window inside which different QWidgets are positioned.

As with QObjects, QWidgets can be created with figure objects to indicate possession, ensuring that items are deleted while they may be now not used. With widgets, those parent-toddler relationships have a further meaning: Each infant widget is displayed within the display screen vicinity occupied via its parent widget. This method that whilst you delete a window widget, all the infant widgets it consists of also are deleted.

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Question 11. What Is Q_object Macro?

Answer :

The Q_OBJECT macro should appear in the non-public phase of a class definition that broadcasts its own signals and slots or that uses different services furnished by means of Qt's meta-object system.

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Question 12. What Is Moc(meta Object Compiler)?

Answer :

The Meta-Object Compiler, moc, is the program that handles Qt's C++ extensions.

The moc device reads a C++ header record. If it reveals one or greater magnificence declarations that comprise the  Q_OBJECT macro, it produces a C++ supply record containing the meta-item code for the ones instructions. Among different matters, meta-item code is needed for the signals and slots mechanism, the run-time type records, and the dynamic property machine.

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Question 13. Which Class Is The Parent Class Of Qline Edit ?

Answer :

QWidget is the determine class to all widgets(push button,line Edit,label like that).

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Question 14. What Is Qml?

Answer :

QML is the call of the language (just like C++, which is some other language...).

QML stands for Qt Meta Language or Qt Modelling Language is a consumer interface markup language.

Question 15. How To Call C++ Call From Qml?

Answer :

QML call C + + strategies with the Qt meta-item system. Like below:

onClicked: determine.Coloration = determine.RandomColor ().

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Question 16. What Are Four Ways Of Integrating C++ With Qml?

Answer :

Subclassing QQuickItem: QQuickItem lets in you to write your very own visible and non-visible QML items the use of C++.

Registering C++ sorts with QML: C++ lessons can be registered with the QML type gadget, permitting them to be instantiated as QML types.

Registering Context Properties: QObjects may be registered with the QML context, allowing their homes to be without delay accessed.

Accessing QML items via the QML object tree: All QML items reside in a tree hierarchy and may be accessed via the foundation of the tree.

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Question 17. How To Call A C++ Function From A Qml?

Answer :

Through setcontext property.

Loading a major.Qml with a simple Item as the root kind via the QqmlApplicationEngine will now not show some thing to your show, as it calls for a window to control a surface for rendering. The engine is able to loading qml code which does not contain any user interface (e.G undeniable objects). Because of this it does now not create a window for you by way of default.
The qmlscene or the new qml runtime will internally first take a look at if the primary qml file carries a window as a root item and if not create one for you and set the root object as a infant to the newly created window.
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Question 18. What Is Q_invokable?

Answer :

Add callable strategies the use of Q_INVOKABLE or Qt slots, and connect with Qt signals with an on Signal syntax.

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Question 19. How To Call A Qml Function From C++?

Answer :

QML functions can be called from C++ and vice-versa.

All QML functions are exposed to the meta-object device and may be called the use of QMetaObject::invokeMethod().

Here is a C++ application that makes use of this to name a QML feature:

// MyItem.Qml

import QtQuick 1.Zero

Item 

    function mysql Function(msg) 

        console.Log("Got message:", msg)

        go back "some go back fee"

    

// primary.Cpp

QDeclarativeEngine engine;

QDeclarativeComponent element(&engine, "MyItem.Qml");

QObject *object = aspect.Writer();

QVariant back Value;

QVariant msg = "Hello from C++";

QMetaObject::invokeMethod(object, "mysql Function",

        Q_RETURN_ARG(QVariant, returned Value),

        Q_ARG(QVariant, msg));

qDebug() << "QML function returned:" << returnedValue.ToString();

delete item;

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