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;
}