Replacing widget pointer in layout

[sandro4912]

I have a Widget which i created in the constructor and placed into a layout.

Game::Game(QWidget *parent) :
    QWidget(parent),
    //...
    mMinefield{ new Minefield},
    //...
{
    auto topLayout = new QHBoxLayout;
    //.. other widgets get added here
    mTopFrame->setLayout(topLayout);

    auto bottomLayout = new QHBoxLayout;
    bottomLayout->addWidget(mMinefield);
    mBottomFrame->setLayout(bottomLayout);

    auto mainLayout = new QVBoxLayout;
    mainLayout->addWidget(mTopFrame);
    mainLayout->addWidget(mBottomFrame);

    mMainFrame->setLayout(mainLayout);

    auto layout = new QVBoxLayout;
    layout->addWidget(mMainFrame);

    setLayout(layout);
}

Now at some point i want to delete this Minefield and replace it with a new one:

I tryed this:

void Game::makeNewMinefield()
{
    delete mMinefield;
    mMinefield = new Minefield;
}

The result is the old widget is gone but i don't see a new one. What is the correct way here to replace the widget?

[SGaist]

Hi,

Set your widget in the layout.

[sandro4912]

@SGaist

What do you mean with that?

[SGaist]

For example use replaceWidget.

[sandro4912]

I tryed this:

void Game::makeNewMinefield()
{
    auto newMinefield = new Minefield;
    auto returnItem = layout()->replaceWidget(mMinefield, newMinefield);
    if(returnItem) {
        qDebug() << "success";
    }
    else {
        qDebug() << "fail";
    }
    mMinefield = newMinefield;
}

but i get fail. It seems like he cant find the old widget event if its already placed.

[SGaist]

Silly question but are you sure you have that widget set in the first place ?

[sandro4912]

@SGaist

I have an idea why its not working.

I put it in a layout in the constructor:

bottomLayout->addWidget(mMinefield);

Then it gets into a QFrame:

mBottomFrame->setLayout(bottomLayout);

Then the two frames i have get played into annother layout

mainLayout->addWidget(mTopFrame);
mainLayout->addWidget(mBottomFrame);

This Layout gets played into annotther frame:

mMainFrame->setLayout(mainLayout);

this frame gets played in annother layout which is the widgets layout:

layout->addWidget(mMainFrame);
    setLayout(layout);

So i guess i have to look for the layout in the frame?

[sandro4912]

I could replace it like this:

void Game::makeNewMinefield()
{
    auto newMinefield = new Minefield{
        mDefaultFieldWidth,
        mDefaultFieldHeight,
        mDefaultMines
    };
    auto returnItem = mBottomFrame->layout()->replaceWidget(
                mMinefield, newMinefield);
    if(returnItem) {
        qDebug() << "success";
    }
    else {
        qDebug() << "fail";
    }
    mMinefield = newMinefield;
}

It seems to work.
Is this the correct way then? What should i do with returnItem in real code?

[SGaist]

Delete it since you won't use its content.

[sandro4912]

Ok I think the issue is solved. Again something learned.

void Game::makeNewMinefield()
{
    auto newMinefield = new Minefield{
        mDefaultFieldWidth,
        mDefaultFieldHeight,
        mDefaultMines
    };
    auto returnItem = mBottomFrame->layout()->replaceWidget(
                mMinefield, newMinefield);

    if(!returnItem) {
        QMessageBox::critical(this, tr("Internal Error"),
                                       tr("Minefield could not be replaced"),
                                       QMessageBox::Close);
        qApp->quit();
    }
    delete returnItem;
    mMinefield = newMinefield;
}