如何自动替换在QtPlainTextEdit小部件中键入的字符

#include <QtWidgets>

class MyPlainTextEdit : public QPlainTextEdit
{
    Q_OBJECT

public:
    MyPlainTextEdit(QWidget *parent = nullptr) : QPlainTextEdit(parent)
    {
        connect(this, &QPlainTextEdit::textChanged, this, &MyPlainTextEdit::replaceText);
    }

private slots:
    void replaceText()
    {
        QTextCursor cursor = textCursor();
        QString currentChar = cursor.block().text().mid(cursor.positionInBlock() - 1, 1);

        // 执行替换操作，这里只是一个示例
        if (currentChar == "a")
        {
            cursor.beginEditBlock();
            cursor.deletePreviousChar();
            cursor.insertText("b");
            cursor.endEditBlock();
        }
    }
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    MyPlainTextEdit textEdit;
    textEdit.show();

    return app.exec();
}

#include "main.moc"