QLayout类和QMainWindow Qt C ++之间的继承

Question

I have a MainWindow class that inherits from QMainWindow. I have another LayoutWindow class that inherits from QLayout. When I declare an instance of the LayoutWindow class, I have an error:

error: invalid new-expression of abstract class type ...

I do not understand because QMainWindow inherits from QWidget which inherits from QLayout?

Here is my code :

Class MainWindow :

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{//instance class LayoutWindow
layoutwindow=new LayoutWindow();

centralArea = new QWidget;
centralArea->setLayout(layoutwindow);
setCentralWidget(centralArea);
}

Class LayoutWindow.h

class LayoutWindow : public QLayout{

Q_OBJECT

public:
LayoutWindow();
};

class LayoutWindow.cpp

LayoutWindow::LayoutWindow(){

 //here is my code
}

Would anyone have some idea of ​​my problem?

Answer 1

QLayout has pure virtual methods, you have to implement these in a subclass you wish to instantiate.

These are

void addItem(QLayoutItem *item);
int count() const;
QLayoutItem * itemAt(int index) const;
QLayoutItem * takeAt(int index);

Your assertion that QWidget inherits QLayout is false, it inherits from QObject and QPaintDevice , both of which have no base classes. QWidget has a layout member , which arranges child widgets.

I also don't think that you need a class that derives from QLayout . You should instead use a combination of objects of existing layout and widget types to arrange your window. You should have, as part of the QT install, a tool for visually designing windows, QDesigner.exe .