Wrong value for ui->textEdit->document()->isModified()



  • I have created a new Qt Widgets Application project with a MainWindow class and a MainWindow.ui file. In MainWindow.ui I've added a QTextEdit widget with its objectName set to textEdit. MainWindow.cpp has the following content:

    @#include "MainWindow.h"
    #include "ui_MainWindow.h"

    #include <QDebug>

    MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
    {
    ui->setupUi(this);

    connect(ui->textEdit->document(), &QTextDocument::modificationChanged,
            this, &MainWindow::on_textEditDocumentModificationChanged);
    
    qDebug() << "before clear():" <<
                ui->textEdit->document()->isModified(); // false
    
    qDebug() << "ui->textEdit->clear():";
    ui->textEdit->clear();
    
    qDebug() << "after clear():" <<
                ui->textEdit->document()->isModified() << // false
                "  [Why here it's false?]";
    

    }

    MainWindow::~MainWindow()
    {
    delete ui;
    }

    void MainWindow::on_textEditDocumentModificationChanged(bool modified)
    {
    qDebug() << " on_textEditDocumentModificationChanged:" <<
    modified << ui->textEdit->document()->isModified(); // true true
    }@

    The on_textEditDocumentModificationChanged slot is called with a 'true' parameter and inside that slot @ui->textEdit->document()->isModified()@ has the value 'true', because calling the clear() method changes the modified status of the document to true, but when the execution returns to the MainWindow constructor, ui->textEdit->document()->isModified() has the value 'false'. I am interested if anyone can reproduce this issue and if there is a solution to this problem.


  • Moderators

    I suspect the textEdit is empty before you call clear(), right? In that case I would consider that to be expected behaviour.



  • Yes but in on_textEditDocumentModificationChanged slot the line @qDebug() << " on_textEditDocumentModificationChanged:" <<
    modified << ui->textEdit->document()->isModified(); // true true@ prints "true true".


  • Moderators

    I would think that it does change the status while checking for changes (when clearing). I understand this might be strange at times, but to me it still looks like a valid behaviour ;)

    What happens if you set some text in your textEdit before clearing?



  • I set some text in the textEdit before clearing and it's the same situation with the same output text.


  • Moderators

    OK, now it finally seems a bit weird to me :-) Sorry it took so long.

    But, when you set the text, does it still show as isModified == false before the clearing?

    Quoting from the documentation:
    [quote]This property holds whether the document has been modified by the user.[/quote]

    I suspect that is the key here: it will return true when modified by the user, but not when being modified programatically. In that light, I think the fact that the state changes briefly when clear() is called is a bug, please report it.



  • In the end I added just below this line:

    @ui->textEdit->clear();@

    the following line:

    @ui->textEdit->document()->setModified(true);@

    This simulates the expected behavior.

    I think that, when I have enough time for this, I will report this bug.

    Thank you for your messages!


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