"this->setEnabled(false);" not always disabling window



  • I am working on a batch image format converter. I have some code:

    @
    // disable the window
    this->setEnabled(false);
    if (outputDir != QString::null)
    {
    // iterate through the items in imageList
    for (int row = 0; row < this->ui->imageList->count(); row++)
    {
    // create a QListWidgetItem from the row
    QListWidgetItem *item = this->ui->imageList->item(row);

            // check to make sure the file exists
            if (!QFile&#40;item->text(&#41;&#41;.exists(&#41;)
            {
                QMessageBox::warning(this, "Error", "Cannot find file '" + item->text() + "'. Check to make sure the file exists.");
                continue;
            }
    
            // convert the image with the selected settings
            if (ImageConverter(NULL).Convert(item->text(), outputDir, QString(this->ui->outputFormatComboBox->currentText()), this->ui->qualitySpinBox->value(), this->ui->overwriteCheckBox->checkState() == Qt::Checked) && this->ui->deleteOriginalCheckBox->checkState() == Qt::Checked)
            {
                // if the image was converter and the user selected deleteOriginalCheckBox, delete the original file
                QFile::remove(item->text());
            }
        }
    }
    else
    {
        // iterate through the items in imageList
        for (int row = 0; row < this->ui->imageList->count(); row++)
        {
            // create a QListWidgetItem from the row
            QListWidgetItem *item = this->ui->imageList->item(row);
    
            // check to make sure the file exists
            if (!QFile&#40;item->text(&#41;&#41;.exists(&#41;)
            {
                QMessageBox::warning(this, "Error", "Cannot find file '" + item->text() + "'. Check to make sure the file exists.");
                continue;
            }
    
            // convert the image with the selected settings
            if (ImageConverter(NULL).Convert(item->text(), QString(this->ui->outputFormatComboBox->currentText()), this->ui->qualitySpinBox->value(), this->ui->overwriteCheckBox->checkState() == Qt::Checked) && this->ui->deleteOriginalCheckBox->checkState() == Qt::Checked)
            {
                // if the image was converter and the user selected deleteOriginalCheckBox, delete the original file
                QFile::remove(item->text());
            }
        }
    }
    // enable the window
    this->setEnabled(true);
    

    }
    @

    to disable the window while the images are being converted. Strangely, the window only appears to be disabled in instances when I display a "QMessageBox" error message.



  • try with:

    @
    QApplication::processEvents();
    @

    after the:

    @
    this->setEnabled(false);
    @



  • Thank you! It works perfectly.



  • The best way is usage another thread for converting (outside gui thread).



  • You don't have to write "this->" to access class members in C++.



  • MTK358:
    I know, but in C# I learned that it is good practice to do so. I think it is because it makes it clearer if there are other functions with the same name. Is it different in C++?



  • [quote author="szh1" date="1286314042"]MTK358:
    I know, but in C# I learned that it is good practice to do so. I think it is because it makes it clearer if there are other functions with the same name. Is it different in C++?[/quote]

    Never heard of such a thing (except for languages like Ruby and Python, which require you to do so).


  • Moderators

    szh1: Yes, using this-> makes it clear you are referring to members, but a good IDE does the same thing using syntax highlighting. So why waste time on the extra typing?

    MTK358: It is not required, but it makes clear that you want to access a member and not e.g. something global. It is perfect valid C++ and can even be necessary to do to disambiguate between things.



  • As far as I know if there is a member function and a global function with the same signature and it is called from within a class the compiler always choose the member.


  • Moderators

    VC15: Yes, of course the compiler uses the scoping rules to resolve names. There are places where this->something and something can be different though. Try this:

    @
    class A {
    public:
    A() : something(5) {}

    void method()
    {
    int something = 7;
    qDebug() << something << this->something;
    }

    private:
    int something;
    };
    @



  • I try to avoid such ambiguity. I realize that this is just an example. But in a real project to have a member and a local variable with the same name is not a good practice.

    Of course, explicit pointing of scope increases readability. When you use this-> or type fully specified class name with the full chain of namespaces it belongs to you won't be surprised during runtime. But this also bloats your code and sometimes decreases readability. So as usual we have to find some compromise.


  • Moderators

    VC15: I fully agree with all you said.

    I do prefer the best practice to avoid variables shadowing others to the best practice of putting "this->" before all member accesses, but both are valid ways to avoid confusing the programmer (not the compiler;-).



  • So I guess it is just preference.


Log in to reply
 

Looks like your connection to Qt Forum was lost, please wait while we try to reconnect.