替换不推荐使用的QtSignalMapper类以转发Qt5中的信号

Question

I have this code which makes a mdi window written for Qt 4:

class MdiWindow : public QMainWindow
{
    Q_OBJECT
public:
    MdiWindow( QWidget *parent = nullptr)

...
private:
    QWorkspace* workspace
    QSignalMapper* mapper
}


MdiWindow::MdiWindow( QWidget *parent ) : QMainWindow( parent )
{
  ...

  workspace = new QWorkspace;
  setCentralWidget( workspace );

  connect( workspace, SIGNAL(windowActivated(QWidget *)), this, SLOT(enableActions()));
  mapper = new QSignalMapper( this );
  connect( mapper, SIGNAL(mapped(QWidget*)), workspace, SLOT(setActiveWindow(QWidget*)) );

  ....
}

According to the QT documentation QWorkspace should be replaced with QMdiArea .

I did that and wrote the first connect like this:

connect(workspace, &QMdiArea::subWindowActivated,
        this, &MdiWindow::enableActions);

But what about QSignalMapper also that is also deprecated.

So how can I update this line:

mapper = new QSignalMapper( this );
connect( mapper, SIGNAL(mapped(QWidget*)), workspace, SLOT(setActiveWindow(QWidget*)) );

I read QSignalMapper can be replaced with lamdas but how in this case? If i understand right mapper forwards all the signals from this to the active window of workspace

Answer 1

Previously you used QSignalMapper::setMapping() to make sure that you'd be sent data you need when the SLOT() was called. Now you can just encapsulate this logic inside a lamba, so if you did (like in Qt example ):

     for (int i = 0; i < texts.size(); ++i) {
         QPushButton *button = new QPushButton(texts[i]);
         connect(button, SIGNAL(clicked()), signalMapper, SLOT(map()));
         signalMapper->setMapping(button, texts[i]);
     }
     connect(signalMapper, SIGNAL(mapped(const QString &)),
             this, SIGNAL(clicked(const QString &)));

you can now do (somewhat):

     for (int i = 0; i < texts.size(); ++i) {
         QPushButton *button = new QPushButton(texts[i]);
         connect(button, &QPushButton::clicked, [=]() {
             emit clicked(texts[i]);
         });
     }

If the setMapping() is not being used, then it probably could have been connected directly to a SLOT() already.