QTextCursor and beginEditBlock

[ecir.hana]

Hello,

I have some text in QPlainTextEdit, where every line starts with 10 spaces:

// example:
 
          line1
          line2
          line3
          line4

// example:

          line1
          line2
          line3
          line4

To copy to clipboard, switch view to plain text mode 

Then, I select few lines and in a loop I want to remove first two spaces from all the selected lines:

// finding the startBlock and endBlock (+1)
 
    cursor.beginEditBlock();
    for (QTextBlock block = startBlock; block != endBlock; block = block.next()) {
        cursor.setPosition(block.position());
        cursor.setPosition(block.position() + 2, QTextCursor::KeepAnchor);
        cursor.removeSelectedText();
    }
    cursor.endEditBlock();

// finding the startBlock and endBlock (+1)
 
    cursor.beginEditBlock();
    for (QTextBlock block = startBlock; block != endBlock; block = block.next()) {
        cursor.setPosition(block.position());
        cursor.setPosition(block.position() + 2, QTextCursor::KeepAnchor);
        cursor.removeSelectedText();
    }
    cursor.endEditBlock();

To copy to clipboard, switch view to plain text mode 

The problem is that the code above “damages” the last selected line – as if it removed some kind of end-of-line marker – when I want to jump to the end of last line the cursor moves to the line below it, between first and second character. Even the selection does not show up properly after the edit – all the lines but the last one have selection indicator expanded to the right window edge and the last line has the indicator only as wide as the line.

// after removing the first two characters:
 
        line1    < 1. selected lines, run the code
        line2    <
        line3    <        < 2. here I jump to end of line
 |      line4
 
 ^ 3. cursor appears here

// after removing the first two characters:

        line1    < 1. selected lines, run the code
        line2    <
        line3    <        < 2. here I jump to end of line
 |      line4
   
 ^ 3. cursor appears here

To copy to clipboard, switch view to plain text mode 

When I remove `beginEditBlock()` and `endEditBlock()` everything works fine.

Please, does anyone know why is this happening?

[wysota]

Please prepare a minimal compilable example reproducing the problem.

[ecir.hana]

Please find the example here: https://bugreports.qt-project.org/browse/QTBUG-30051

[wysota]

This works correctly for me:

#include <QtWidgets>
 
int main(int argc, char **argv) {
	QApplication app(argc, argv);
	QPlainTextEdit edit;
	edit.insertPlainText("    aaa\n    aaa\n    aaa\n    aaa");
	QTextBlock block = edit.document()->findBlock(0);
	QTextCursor cursor = edit.textCursor();
	cursor.beginEditBlock();
	for (int i = 0; i < 3; i++) {
		cursor.setPosition(block.position());
		cursor.setPosition(block.position() + 2, QTextCursor::KeepAnchor);
		cursor.removeSelectedText();
		block = block.next();
	}
	cursor.endEditBlock();
	edit.show();
	return app.exec();
}

#include <QtWidgets>

int main(int argc, char **argv) {
	QApplication app(argc, argv);
	QPlainTextEdit edit;
	edit.insertPlainText("    aaa\n    aaa\n    aaa\n    aaa");
	QTextBlock block = edit.document()->findBlock(0);
	QTextCursor cursor = edit.textCursor();
	cursor.beginEditBlock();
	for (int i = 0; i < 3; i++) {
		cursor.setPosition(block.position());
		cursor.setPosition(block.position() + 2, QTextCursor::KeepAnchor);
		cursor.removeSelectedText();
		block = block.next();
	}
	cursor.endEditBlock();
	edit.show();
	return app.exec();
}

To copy to clipboard, switch view to plain text mode 

[ecir.hana]

Thank you for the reply!

Yes, it works - but I don't understand...how is it different from the example I wrote? Does the example work for you?

The problem is, I would like the removing to be trigged by shortcut, not sure how to translate your code because I'll basically end up with what I already have, no? Sorry, I'm really confused why your code works and mine does not.

[wysota]

The only difference I can see between your code and mine is that in my case the code is ran before the widget is first shown on screen (thus before the document is first laid out)

[ecir.hana]

Hmm....exactly. That's really unfortunate as I need to run the code after the widget is drawn. Please, do you have any idea why is this happening?

[wysota]

We have no idea yet what is happening. You didn't verify that my code breaks when you first show the widget (and process its events) and then modify content.

[ecir.hana]

You didn't verify that my code breaks when you first show the widget (and process its events) and then modify content.

It breaks. (when I move "edit.show();" somewhere above "cursor.beginEditBlock();", that is...)

[wysota]

show() only schedules the widget for display. It does not display it. You need to process events first. Either way, if it breaks then maybe something is wrong with the document layout engine.

[ecir.hana]

I'm sorry I'm not sure I understand - I'm very new to Qt. Do you mean something like:

#include "mainwindow.h"
#include <QtWidgets>
 
int main(int argc, char **argv) {
QApplication app(argc, argv);
QPlainTextEdit edit;
edit.insertPlainText(" aaa\n aaa\n aaa\n aaa");
edit.show();
 
app.processEvents();
 
QTextBlock block = edit.document()->findBlock(0);
QTextCursor cursor = edit.textCursor();
cursor.beginEditBlock();
for (int i = 0; i < 3; i++) {
cursor.setPosition(block.position());
cursor.setPosition(block.position() + 2, QTextCursor::KeepAnchor);
cursor.removeSelectedText();
block = block.next();
}
cursor.endEditBlock();
 
return app.exec();
}

#include "mainwindow.h"
#include <QtWidgets>

int main(int argc, char **argv) {
QApplication app(argc, argv);
QPlainTextEdit edit;
edit.insertPlainText(" aaa\n aaa\n aaa\n aaa");
edit.show();

app.processEvents();

QTextBlock block = edit.document()->findBlock(0);
QTextCursor cursor = edit.textCursor();
cursor.beginEditBlock();
for (int i = 0; i < 3; i++) {
cursor.setPosition(block.position());
cursor.setPosition(block.position() + 2, QTextCursor::KeepAnchor);
cursor.removeSelectedText();
block = block.next();
}
cursor.endEditBlock();

return app.exec();
}

To copy to clipboard, switch view to plain text mode 

Also, the code I posted processes all the events and then modifies the code, is this correct?

[wysota]

I don't see how beginEditBlock() could break anything since all it does is to increment two internal counters. endEditBlock() correctly decrements the one that needs it.

[ecir.hana]

I don't see how beginEditBlock() could break anything

The code I posted, does it work for you?

[norobro]

Try your code with a QTextEdit.

[ecir.hana]

In QTextEdit it works. But it would be really great if it worked in QPlainTextEdit too...

[norobro]

But it would be really great if it worked in QPlainTextEdit too...

Why so? I'm interested because another poster said the same thing (link) about a scrolling problem he was having with QPlainTextEdit.

[ecir.hana]

Why so?

Well...because it seems it's a bug and because QPlainTextEdit si faster than QTextEdit.