CODEWITHSUNDEEP
c++qt
Theodore Tang
Theodore Tang

Reputation: 1021

Qt Can't set centralWidget() properly

I tried to build a simple GUI application. Then I got those warnings: 

QLayout: Attempting to add QLayout "" to MainWindow "", which already has a layout
QWidget::setLayout: Attempting to set QLayout "" on MainWindow "", which already has a layout

I googled that you have to set central widget in MainWindow. And here is my implement which is still not working:

.h

class MainWindow : public QMainWindow
{
    Q_OBJECT
    QWidget *centralWidget;

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

    void setButtons();
    ...
private:
    Ui::MainWindow *ui;
    QPushButton *btn[9][9];
}


.cpp

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    centralWidget = new QWidget(this);
    this->setCentralWidget(centralWidget);
    ...
}

void MainWindow::setButtons()
{
    for(int i = 0; i < 9; i++) {
        for(int j = 0; j < 9; j++) {
            btn[i][j] = new QPushButton(this);
            ...
            QVBoxLayout *vLayout = new QVBoxLayout(this);
            vLayout->addWidget(btn[i][j]);
            centralWidget->setLayout(vLayout);
        }
    }
}

After trying this, I still received the warning messages, how can I solve this problem?

Thanks.

Upvotes: 0

Views: 614

Answers (1)

G.M.
G.M.

Reputation: 12879

Your code has two basic issues. Firstly, the statement...

 QVBoxLayout *vLayout = new QVBoxLayout(this);

will instantiate a new QVBoxLayout with this as its parent. Since this is of type MainWindow * and MainWindow inherits from QMainWindow you are effectively calling QMainWindow::setLayout -- that's the source of the error message...

QLayout: Attempting to add QLayout "" to MainWindow "", which already has a layout

Secondly, you're creating a new QVBoxLayout on each loop iteration. If you really do want the buttons vertically aligned in a layout try something like...

void MainWindow::setButtons ()
{
  QVBoxLayout *vLayout = new QVBoxLayout(centralWidget);
  for (int i = 0; i < 9; i++) {
    for (int j = 0; j < 9; j++) {
      btn[i][j] = new QPushButton;
        ...
      vLayout->addWidget(btn[i][j]);
    }
  }
}

Upvotes: 2

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