CODEWITHSUNDEEP
qt
shashi
shashi

Reputation: 27

QT designer implementation error

Actually i activated the Qt creator from terminal ex: in Linux sudo Qt-creator.sh. so qt application opens.when i tried to design the UI by drag and dropping the buttons , widgets to form a type of UI.when i run the application , it just show the blank widget. the designed part done in UI is not implemented. so whatever changes done in UI designer, is not displaying when i run application. i don't no where is the issue. is it because of activating the qt from terminal.

the reason for activating qt creator from terminal because, i need to cross compile the binary code for Arm-Cortex controller. so i need to follow the steps for setting compiler for arm-cortex in qt application.however the cross compilation works. but if any changes done on qt designer, when i run the application , i cant able to see the changes in UI output window.

Upvotes: -1

Views: 793

Answers (1)

iksemyonov
iksemyonov

Reputation: 4196

Let me start by providing some background. The Qt library allows you to create graphical user interfaces (GUI) using two alternative methods:

  • QWidgets

  • Qt Quick

QWidgets uses a set of widgets written in C++ that you can either create and layout yourself using explicit C++ code, i.e. manually, or use Qt Designer to edit the interface of your applicaiton in a WYSWIG style, producing a .ui. file that you use in a certain way later on. Qt Quick uses a declarative approach to creation of the user interfaces, with a special markup language similar to HMTL. We're not discussing it here as it's not the approach that you're using.

Now let's take a closer look at how Qt Designer works in conjunction with .ui. files, given that our application is written in C+.

Once you launch Qt Designer and edit a form, then save it, a .ui. file is produced. It's an XML file containing an hierarchical description of the UI you've created. However, to be able to use that form as the GUI of your application, additional steps are required. You need to "tell" the application to use this .ui. file. This is done as follows. A special executable, the UI compiler uic, is invoked (automatically via qmake or cmake) to process the .ui file, and generate C++ code in form of a header file. You then include the header file in the file that includes your application code, and use one of the three available methods to create the UI of your application using the generated code.

The simplest method is shown below.

class MyForm : public QWidget
{
    Q_OBJECT

public:
    MyForm(QWidget *parent = 0);

private:
    Ui::MyForm ui;
};

The ui member object is an object of the class generated by uic - the UI compiler mentioned above. The class contains code for creating the user interface, organizing it into a layout, and managing it throughout the application lifetime.

Then, in the .cpp file, we have the constructor:

MyForm::MyForm(QWidget *parent)
    : QWidget(parent)
{
    ui.setupUi(this);
}

The important call here is ui.setupUi(this). This creates the UI elements, applies the layout, and sets the layout on the widget provided as the argument to this call. Remember, our class inherits from QWidget.

The other approaches include inheriting from the generated class and dynamically loading the .ui file, omitting the compilation by uic, using the QUiLoader class. Please consult http://doc.qt.io/qt-5/designer-using-a-ui-file.html for further reference.

As far as starting Qt Designer from terminal, it has no effect on the problem. Moreover, starting a GUI application as root is highly discouraged on Linux, as it poses a major security issue.

Upvotes: 1

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