Custom widget can't show in layout

[jjjkk]

I code a custom widget and put it in the main layout in my mainwindow class .
But It can't show properly as below:

the blank part should be the custom widget.
I change the code generate by ui file from:

        graphicsView = new MainViewer(aaa);
        graphicsView->setObjectName(QString::fromUtf8("graphicsView"));

        gridLayout->addWidget(graphicsView, 3, 1, 1, 1);

        MainWindow->setCentralWidget(aaa);

to:

        graphicsView = new MainViewer(aaa);
        graphicsView->setObjectName(QString::fromUtf8("graphicsView"));

        //gridLayout->addWidget(graphicsView, 3, 1, 1, 1);

        MainWindow->setCentralWidget(aaa);

I can get a floating custom widget as below:

And if I set the custom widget as central widget, It also work well.

So, what may be the problem when I put the custom widget into a layout?

[mrjj]

Hi
There is no special requirements for a custom widget to be used in a layout but maybe it get compressed to zero in size
so try for test to do
mywidget->setMinimumSize(100,100) and see.

[JoeCFD]

void QGridLayout::addWidget(QWidget *widget, int fromRow, int fromColumn, int rowSpan, int columnSpan, Qt::Alignment alignment = Qt::Alignment())

gridLayout->addWidget(graphicsView, 1, 0, 3, 1);