When inserting 4 spaces or a tab to QPlainTextEdit, i can't delete them

Fuchsiaff

Whenever I do this->insertPlainText(" "); then the spaces that were added, I can't delete them.

But when I do the same thing in python, using PyQt5 like this self.insertPlainText(" ") Then i can delete the 4 spaces that were inserted.

Why is it like this?

mrjj

Hi
You mean the spaces stay when you press delete button or in
what way, cannot delete ?
It should be the same between python or c++. it calls same function in Qt.

So maybe its some sort of unicode thing. I tried test on windows, but
it deleted fine.

So on what Qt version and platform do you see this ?

Fuchsiaff

Alright, maybe it is something to do with my code then, here is my Plaintextedit class that subclasses qplaintextedit:

#include <QFont>
#include <QDebug>
#include <iostream>

PlainTextEdit::PlainTextEdit(QWidget *parent) {

    font = new QFont;

    font->setFamily("Consolas");
    font->setPointSize(12);

    replace_tabs = 4;
    key_list = {16777217, 16777219, 16777220};
    this->setTabStopWidth(40);
    this->createStandardContextMenu();
    this->setWordWrapMode(QTextOption::NoWrap);
}

void PlainTextEdit::move_cursor_back() {

    QTextCursor text_cursor = this->textCursor();
    int text_cursor_pos = text_cursor.position();

    text_cursor.setPosition(text_cursor_pos -1);
    this->setTextCursor(text_cursor);
}

void PlainTextEdit::keyPressEvent(QKeyEvent *e) {

    QTextCursor text_cursor = this->textCursor();
    int key = e->key();

    if (key == Qt::Key_QuoteDbl) {
        this->insertPlainText("\"");
        move_cursor_back();
    }

    if (e->modifiers() == Qt::ControlModifier && e->key() == 61) {

        this->font->setPointSize(font->pointSize() + 1);
        this->setFont(*font);
    }

    if (e->modifiers() == Qt::ControlModifier && e->key() == 45) {

        this->font->setPointSize(font->pointSize() - 1);
        this->setFont(*font);
    }

    if (key == 39) {

        this->insertPlainText("'");
        move_cursor_back();
    }

    if (key == Qt::Key_BraceLeft) {

        this->insertPlainText("}");
        move_cursor_back();
    }

    if (key == Qt::Key_BracketLeft) {

        this->insertPlainText("]");
        move_cursor_back();
    }

    if (key == Qt::Key_ParenLeft) {

        this->insertPlainText(")");
        move_cursor_back();
    }

    if (!key_list.contains(key)) {
        QPlainTextEdit::keyPressEvent(e);
        return;
    }

   // e->accept();

    if (key == 16777217 && replace_tabs) {
        int amount = 4 - this->textCursor().positionInBlock() % 4;
        QString str = " ";

        this->insertPlainText(str.repeated(amount));

    } else if (key == 16777219 && this->textCursor().selectionStart() == this->textCursor().selectionEnd() && replace_tabs && this->textCursor().positionInBlock()) {

        int position = this->textCursor().positionInBlock();
        int end = this->textCursor().position();
        int start = end - (position % 4);

        if (start == end && position >= 4) {

            start -= 4;
        }
        QString string = this->toPlainText().mid(start, end);
        QString stripped_string = string.trimmed();
        if (!stripped_string.length()) {

            for (int i; i < end - start; i++) {
                this->textCursor().deletePreviousChar();

            }
        } else {
            QPlainTextEdit::keyPressEvent(e);
        }

    } else if (key == 16777220) {
        int end = this->textCursor().position();
        int start = end - this->textCursor().positionInBlock();
        QString line = this->toPlainText().mid(start, end);
        int indentation = line.length() - line.trimmed().length();

        QString chars = "\t";

        if (replace_tabs) {
            chars = "    ";
            indentation /= replace_tabs;
           // QPlainTextEdit::keyPressEvent(e);
        }

        if (line.endsWith(":")) {
            qDebug() << line.endsWith(":");
            if (replace_tabs) {
                indentation += 1;
            }

            QPlainTextEdit::keyPressEvent(e);
            this->insertPlainText(chars.repeated(indentation));

        } else {
            QPlainTextEdit::keyPressEvent(e);
            this->insertPlainText(chars.repeated(indentation));
        }
    } else {
        QPlainTextEdit::keyPressEvent(e);
    }
}

and the header file:

#define PLAINTEXTEDIT_H
#include <QPlainTextEdit>

class PlainTextEdit : public QPlainTextEdit {

public:
    PlainTextEdit(QWidget *parent = nullptr);
    QFont *font;
    void move_cursor_back();
    int replace_tabs;
    QList<int> key_list;

protected:
    void keyPressEvent(QKeyEvent *event) override;
};

#endif // PLAINTEXTEDIT_H

Fuchsiaff

I still have no idea how to fix it :(

mrjj

@Fuchsiaff

Hi
You should try with clean default GUI project and see if still happens.
It could be inside Qt somehow.

also ,what happens if u put break point in keyPressEvent
and follow program with single step pressing the delete ?

update:
fast tried with your subclass and it hung the app when trying to delete spaces
so its fair to say its just some bug.

mrjj

Hi
Bug was that there was an uninitialized variable in for loop causing it to
skip/malfunction

in the

else if (key == 16777219 && ....

if (!stripped_string.length()) {

            for (int i=0; i < end - start; i++) { <<<< was not set to zero
                this->textCursor().deletePreviousChar();

            }

alt text

after setting it, it seems to work for me.

Final note: Using magic numbers for all keys even when they do they have keycodes
is a not optimal. It makes the logic much harder to read.

Fuchsiaff

Thank you, but here is another question:
Before I saw your solution, I compiled it in release mode and it worked perfectly.
Why does it work in release mode and not in debug mode?

aha_1980

@Fuchsiaff because you had luck.

undefined behaviour may result in anything: correct operation, data disturbance or crashes. it's just undefined.

JonB

@Fuchsiaff
To clarify further from @aha_1980: i was uninitialized. Its starting value was undefined. Specifically, it would have taken the value of whatever happened to be in memory where it was allocated. Now, between Debug & Release modes it is not uncommon for a memory location to be zero in one and something non-zero in the other (or indeed any two numbers).

There is a moral here: when you see such a difference in behaviour in your code between Debug & Release, one of the first things you should be thinking about is the possibility of an uninitialized variable, an undefined function return result, etc.