如何使Qt Mainwindow彼此连接？

Question

I created two QMainWindow class ui in Qt. MainWindowB is shown after clicking a button in MainWindowA. I want to attach MainWindowB to MainWindowA (when the two mainwindows are moved close, they snap together like magnets), so that they can be moved together as "attached". If they are dragged apart, they will be just regular QMainWindow. How can I make that happen?

I tried to use QDockWidget but when it "attached" (docked), it affects other components in the original MainWindowA.

mainwindowA.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_pushButton_clicked()
{
    MainWindowB *newWin= new MainWindowB;
    newWin->show();
}

mainwindowB.cpp

#include "mainwindowb.h"
#include "ui_mainwindowb.h"

MainWindowB::MainWindowB(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindowB)
{
    ui->setupUi(this);
}

MainWindowB::~MainWindowB()
{
    delete ui;
}

Answer 1

You can implement this pretty straightforward:

#include <QApplication>
#include <QMainWindow>

class CMasterWindow : public QMainWindow
{
    Q_OBJECT

public:
    CMasterWindow(QWidget *parent = Q_NULLPTR)
        : QMainWindow(parent)
    {
        setWindowTitle(tr("master"));
    }

    ~CMasterWindow() { }

    virtual void moveEvent(QMoveEvent *me) Q_DECL_OVERRIDE
    {
        QMainWindow::moveEvent(me);
        emit SignalMoved(QRect(pos(), size()));
    }

    virtual void resizeEvent(QResizeEvent *re) Q_DECL_OVERRIDE
    {
        QMainWindow::resizeEvent(re);
        emit SignalMoved(QRect(pos(), size()));
    }

signals:
    void SignalMoved(QRect const &r);
};

class CSlaveWindow : public QMainWindow
{
    Q_OBJECT

public:
    CSlaveWindow(CMasterWindow *master)
        : QMainWindow(master),
        mpMaster(master),
        mbLocked(master != Q_NULLPTR)
    {
        setWindowTitle(tr("slave"));
        if(mpMaster != Q_NULLPTR)
        {
            bool ok = connect(mpMaster, &CMasterWindow::SignalMoved, this, &CSlaveWindow::MasterMovedSlot);
            Q_ASSERT(ok);
            mMasterRect = QRect(mpMaster->pos(), mpMaster->size());
            MasterMovedSlot(mMasterRect);
        }
    }
    ~CSlaveWindow() { }

    static int const snapMargin = 16;

    virtual void moveEvent(QMoveEvent *me) Q_DECL_OVERRIDE
    {
        QMainWindow::moveEvent(me);
        if(pos() == mExpectedMove)
        {
            // ignore self-initiated move (from MasterMovedSlot())
            return;
        }

        mbLocked = QRect(mMasterRect.topRight(), 2 * QSize(snapMargin, snapMargin)).intersects(QRect(pos(), QSize(snapMargin, snapMargin)));
        MasterMovedSlot(mMasterRect);
    }

private slots:
    void MasterMovedSlot(QRect const &r)
    {
        if(mbLocked)
        {
            mExpectedMove = r.topRight() + QPoint(snapMargin, 0);
            move(mExpectedMove);
        }
        mMasterRect = r;
    }

private:
    CMasterWindow *mpMaster;
    bool mbLocked;
    QPoint mExpectedMove;
    QRect mMasterRect;
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    CMasterWindow *master = new CMasterWindow();
    master->show();
    (new CSlaveWindow(master))->show();

    return a.exec();
}

You need to define one window as master and the other one as slave - else you won't be able to tell the difference between the user wanting to move both windows together or wanting to tear one window from the other.