list of qtextedit. How to get the one that has changed?

LeoC

Hey,

this one works absolutely fine:

QTextEdit *textEdit ;

void MainWindow::doStuff() {
    textEdit = new QTextEdit();
    connect(textEdit,SIGNAL(cursorPositionChanged()),this,SLOT(texthaschanged()));
}

void MainWindow::texthaschanged() {
    QTextCursor myCursor;
    myCursor = textEdit ->textCursor();
    qDebug() << "text has changed at position" << myCursor.position();
}

But what to do when I have the following?

QList<QTextEdit*> myList;

How do I know now which cursor has changed?

Thanks!

JonB

@LeoC
You read up about C++ lambdas. :)

void MainWindow::doStuff() {
    QTextEdit *textEdit = new QTextEdit();
    myList.append(textEdit);
    connect(textEdit, &QTextEdit::cursorPositionChanged,
            this, [this](QTextEdit *textEdit) { texthaschanged(textEdit);  } );
}

void MainWindow::texthaschanged(QTextEdit *textEdit) {
    ...
}

This passes the textEdit emitting the signal as a parameter to the texthaschanged(QTextEdit *textEdit) slot, so it uses that to access that one in the body of the method.

We are no longer using the single member variable QTextEdit *textEdit ; you had. You get rid of that, and use your QList<QTextEdit*> myList to store pointers to the various QTextEdits.

You also use this opportunity to start using the new style signals & slots syntax instead of the SIGNAL/SLOT() macros. You get better edit/compile-time support.

EDIT @KroMignon has corrected my (untested!) code below :) The connect() statement should read:

    connect(textEdit, &QTextEdit::cursorPositionChanged,
            this, [this, textEdit]() { texthaschanged(textEdit);  } );

LeoC

@JonB thanks for your answer.

To be honest, I am not very familiar with lambdas. I just started reading about it and I think I got a basic understanding of it.

Nevertheless I can't get your example working. I get the following error:

error: static assertion failed: Signal and slot arguments are not compatible.

Can you give ma a hint for this?

KroMignon

@LeoC said in list of qtextedit. How to get the one that has changed?:

Can you give ma a hint for this?

There is a little error in proposed code, QTextEdit::cursorPositionChanged() don't have arguments!
You have to capture booth variable to use lambdas, like this:

void MainWindow::doStuff() {
    QTextEdit *textEdit = new QTextEdit();
    myList.append(textEdit);
    connect(textEdit, &QTextEdit::cursorPositionChanged,
            this, [this, textEdit]() { texthaschanged(textEdit);  } );
}

I could suggest you to take a look at https://blog.feabhas.com/2014/03/demystifying-c-lambdas/ to better understand lambda functions usage in C++.
And this for combining lambdas and Qt: https://medium.com/genymobile/how-c-lambda-expressions-can-improve-your-qt-code-8cd524f4ed9f

LeoC

@KroMignon thanks. I guess I figured it out. This one works fine:

    for(int i_Ctr = 0; i_Ctr < 3; i_Ctr++) {
        QTextEdit *textEdit = new QTextEdit();

        connect(textEdit, &QTextEdit::cursorPositionChanged, [this, textEdit] {
            this->texthaschanged(textEdit);
        });
        textEdit->show();
    }

In my previous example the definition of QTextEdit wasn't part of the function itself but rather part of the h-file. That was something I just didn't recognized.
Anyway, now I can move on :) Thank you!