QProgressBar doesn't update

Sucharek

Hi, I'm trying to make a progress bar for a file download, but I can't get it to work.
I'm sending information from a thread to mainwindow, where the progress bar should update, but it doesn't do anything
Here's what I have:

QProgressBar* progBar = new QProgressBar;
if (percentage < 0) {
    ui->gridLayout_Content->addWidget(progBar);
} else if (percentage > 0) {
    qDebug() << percentage; //this works, but progBar doesn't update
    progBar->setValue(percentage);
    progBar->update();
} else if (percentage > 100) {
    delete progBar;
}

JonB

@Sucharek
In principle the approach should work.

Where is this code?
If it is really as shown, you would create a new progress bar each time this code is called to show a new value. Also is it ever called with percentage < 0? Maybe one of these is your issue, I don't know.
Make sure you really are sending a signal from the thread and the code above is in the main UI thread, in a slot.
If your percentage is 0--100, verify what the progress bar's range is.

Sucharek

Hi @JonB, the code is as a private slot (void) in MainWindow.
I'm calling percentage < 0 before the download starts.
I didn't set the range, so I did that, but nothing changed.
I know that the percentage values are being sent, because when I run qDebug(), it prints the percentages just fine.

JonB

@Sucharek
Show your actual code, like I said it can't be right to have what you presently show.

Sucharek

Ok
Here is the full void in MainWindow.

void MainWindow::progressBar(int percentage)
{
    QProgressBar* progBar = new QProgressBar;
    progBar->setRange(0, 100);
    if (percentage < 0) {
        ui->gridLayout_Content->addWidget(progBar);
    } else if (percentage > 0) {
        qDebug() << percentage;
        progBar->setValue(percentage);
        progBar->update();
    } else if (percentage > 100) {
        delete progBar;
    }
}

Here is the connector:

QObject::connect(&fT,SIGNAL(progBar(const int&)),SLOT(progressBar(const int&)), Qt::QueuedConnection);

Code in thread:

//start download
progBar(-1);
while(true) {
    QString percentage = getPercentage(dir + "ROM/");
    dlProg = "Downloading ROM... (" + percentage + "%)"; update(checkInternet + dlProg); //I'm also updating a label, where the percentage was shown originally
    progBar(percentage.toInt()); //here I'm emiting the percentage values

    avoidComplete += 1;
    if (avoidComplete > 40) {if (percentage == "100") {progBar(101); /*this is hide the bar after finished*/ break;}}

    msleep(100);
}

JonB

@Sucharek
In that case please re-read my first answer. I gave you 4 possibilities. You answered for 3 of them sataisfactorily. The one you ignored is what is wrong in your code.

On a separate stylistic matter:

Use emit as a matter of course when emitting signals.
Don't specify Qt::QueuedConnection explicitly, let Qt figure that for you when the signal & slot are not in the same thread.

jsulm

This post is deleted!

JonB

This post is deleted!

J.Hilk

@Sucharek besides all the other issues you have with your code,

your QPorgressbar does neither have a QWidget parent, that is visible, nor do you call show on it

-> you never see any of the countless QProgressbar widgets you create.

Sucharek

@JonB, I used emit, nothing changed.
I replace Qt::QueuedConnection to Qt::AutoConnection, but that also didn't do anything.

JonB

@Sucharek
I said those two were stylistic.

I already typed in what is wrong in your code. I told you there were 4 bullet points. I told you you had answered 3 of them satisfactorily. I told you that the one you ignored is what is wrong with your code. Also in @J-Hilk's post he mentions the same issue at one point. I don't feel like re-typing it when it's already there. If you still need help on it come back, but at least take the time to read which one you ignored first.....

SPlatten

@Sucharek , looking at your source, you create a new progress bar in a function:

void MainWindow::progressBar(int percentage)
{
    QProgressBar* progBar = new QProgressBar;

Some place elsewhere you then connect a signal and slot:

QObject::connect(&fT,SIGNAL(progBar(const int&)),SLOT(progressBar(const int&)), Qt::QueuedConnection);

What is fT, is this actually in the same place as you create the progress bar?

What version of Qt are you using? progBar isn't a progress bar signal.

Sucharek

Hi @SPlatten, fT is the thread name.
The QObject::connect calls the MainWindow::progBar slot.

I'm using Qt 5.15.2 (static).

SPlatten

@Sucharek , I suggest you get it working with simple code first. Also isn't your connect missing the pointer to the progress bar as the third parameter ?

Sucharek

@JonB, ok, I think I understood the 4th solution.
I created a new progress bar everytime I called the progBar signal in the thread.
It's basically like this: create -> delete -> create -> delete -> ...
Here's my code:

delete progBar;
progBar = new QProgressBar; //progBar is now a global variable in MainWindow
progBar->setRange(0, 100);
if (percentage < 0) {
    ui->gridLayout_Content->addWidget(progBar);
} else if (percentage > 0) {
    qDebug() << percentage;
    ui->gridLayout_Content->addWidget(progBar);
    progBar->setValue(percentage);
    progBar->update();
} else if (percentage > 100) {
    delete progBar;
}

I don't know if that's what you meant, but the most important thing is, that it worked. Thanks

JonB

@Sucharek said in QProgressBar doesn't update:

I created a new progress bar everytime I called the progBar signal in the thread.

:) Well done, it's important to see things for yourself!

However, it still looks like you have progBar = new QProgressBar; in your slot?? The first 3 lines need to be somewhere else, either outside the slot or maybe in the if (percentage < 0) case.

Oh, and hang on! You have moved [copied] ui->gridLayout_Content->addWidget(progBar); into the case for every percentage update! That's not right [fortunately it won't have any effect]. That too belongs e.g. in the if (percentage < 0), or where you create the progress bar.

Also, be careful about you have two delete progBar;s. And you do not set the member variable to nullptr either time. This is waiting to crash on you with a "duplicate delete".....

Sucharek

I moved these lines in to initialization void (the one with ui->setup(this)).
I know aboult the duplicate deletes. Thanks for reminding me.