Why the slot function cannot insert text even if it's successfully called

Question

I'm writing a code editor in Qt with QScintilla.

I want to automatically complete the back brackets when I enter the front brackets. So that I connect the cursorPositionChanged(int, int) signal to complete_braces() slot and the connection works. But the insert() statement doesn't work even if the slot function is called.

This is for a Windows 10 PC, running Qt 5.13.0(MinGW 7.3.0 32-bit), Qt Creator 4.9.2, QScintilla 2.11.2.
The connection of signal and slot works because the qDebug() statement output correctly.
When I connect a toolbar button trigger to the slot function and push the button. The back brace is placed correctly.
The insert(QString) function works when I call it in normal functions.

Header:

/* codeeditor.h */
class CodeEditor : public QsciScintilla
{
    Q_OBJECT
...

public slots:
    void complete_brackets();
...
};

Code:

/* codeeditor.cpp */
CodeEditor::CodeEditor()
{
...
    // Slots
    connect(this, SIGNAL(textChanged()),
            this, SLOT(complete_brackets()));
...
}
...
void CodeEditor::complete_brackets()
{
    int line, index;
    getCursorPosition(&line, &index);
    if (text(line)[index] == '(')
    {
        qDebug() << "Get a bracket"; // This statement works.
        insert(QString(")")); // This statement doesn't work.
    }
}
...

I expected the insert(QString) function in the slot function to be called correctly, but it doesn't.

How can I do to make the insert statement effective or, is there any other method to auto complete the brackets?

score 1 · Accepted Answer · answered Jul 27 '19 at 19:16

It seems that QsciScintilla does not allow adding text in the slot connected to the textChanged signal, a possible solution is to add it a moment later using a QTimer::singleShot():

void CodeEditor::complete_brackets(){
    int line, index;
    getCursorPosition(&line, &index);
    if (text(line)[index] == '(')
        QTimer::singleShot(0, [this, line, index](){
          insert(")");
          setCursorPosition(line, index+2);
        });
}

On the other hand it is recommended that you use the new connection syntax:

connect(this, &QsciScintilla::textChanged, this, &CodeEditor::complete_brackets);

It works, thank you! However, when I use the new connection syntax, an error will occur that `"QObject::connect: signal not found in CodeEditor"`, but the old connection syntax works well. I don't know why it happened. — DCTewi, Jul 28 '19 at 02:01

Why the slot function cannot insert text even if it's successfully called

1 Answers1