No show of QPixmap

Stan Huang

Below is snippet of my codes which I expected it to show a specified BMP picture, but it doesn't. Anything I missed? I see that "to create ..." and "Created ..." shown, but see no picture shown. I confirmed the picture existing too.

				printf ("to create a QPixmap\n");
				pixmap_RoadFault = QPixmap("/exe/bv/image/sdkpic.jpg").scaled(74,45);
				printf ("Created a QPixmap\n");
				palette_RoadFault.setBrush(QPalette::Background, QBrush(pixmap_RoadFault));
                                    palette_RoadFault.setBrush(QPalette::Background, QBrush(pixmap_RoadFault));
				ui->label_RoadFault->setGeometry(480,120,80,50);
				ui->label_RoadFault->setPalette(palette_RoadFault);
				ui->label_RoadFault->setAutoFillBackground(true)

JKSH

@Stan-Huang It's not clear from your snippet: What does palette_RoadFault do?

The quickest way to show your QPixmap is to put inside a QLabel and show() the QLabel.

Stan Huang

@JKSH I updated the snippet. I don't quite understand it because it was from previous engineer and he said this is not verified codes. I am still new Qt user.

Christian Ehrlicher

When I see your other (deleted) question here https://forum.qt.io/topic/99218 I would guess /exe/bv/image/sdkpic.jpg does not exist or is not readable. You can check if the QPixmap is empty: http://doc.qt.io/qt-5/qpixmap.html#isNull

Stan Huang

@Christian-Ehrlicher You're right in saying non-existence of picture to be shown being the cause of issue stated at the deleted one. But for this one, I'm sure it's existent and readable.

JKSH

@Stan-Huang said in No show of QPixmap:

I am still new Qt user.

Then it's best to study simple examples.

Create a new, small Qt Widgets application:

#include <QApplication>
#include <QPixmap>
#include <QLabel>

int main (int argc, char **argv)
{
    QApplication app(argc, argv);

    QPixmap pixmap_RoadFault("/exe/bv/image/sdkpic.jpg");

    QLabel label;
    label.setPixmap(pixmap_RoadFault);
    label.show();

    return app.exec();
}

By the way, I've restored your other post. Please don't delete posts after you have found a solution.

Christian Ehrlicher

@Stan-Huang said in No show of QPixmap:

I'm sure it's existent and readable.

Although you are 'sure' you should check it with the function I pointed you to ...

Stan Huang

@JKSH It still doesn't work.

SGaist

Hi,

What does file /exe/bv/image/sdkpic.jpg return ?

jsulm

@Stan-Huang Come on, be a bit more proactive!
Did you check whether your pixmap is null as @Christian-Ehrlicher suggested?
Also, /exe/bv/image/sdkpic.jpg is an absolute path and looks strange - are you REALLY sure it is correct?
Try what @SGaist suggested.

Stan Huang

@SGaist The return of "file /exe/bv/image/sdkpic.jpg" is:

root@mitacimx6:/opt/BVDemo/smartbox# file /exe/bv/image/sdkpic.jpg
/exe/bv/image/sdkpic.jpg: JPEG image data, JFIF standard 1.01, aspect ratio, density 1x1, segment length 16, baseline, precision 8, 1108x1478, frames 3

JKSH

@Stan-Huang said in No show of QPixmap:

The return of "file /exe/bv/image/sdkpic.jpg" is:

root@mitacimx6:/opt/BVDemo/smartbox# file /exe/bv/image/sdkpic.jpg
/exe/bv/image/sdkpic.jpg: JPEG image data, JFIF standard 1.01, aspect ratio, density 1x1, segment length 16, baseline, precision 8, 1108x1478, frames 3

OK, it looks like the file is valid.

Next, check if Qt can understand the file format. What do you get when you call
qDebug() << QImageReader::supportedImageFormats() ? (remember #include <QDebug> and #include <QImageReader>)

Stan Huang

@Christian-Ehrlicher setPixmap(pixmap_RoadFault) is void, so no return.

Christian Ehrlicher

@Stan-Huang said in No show of QPixmap:

setPixmap(pixmap_RoadFault) is void, so no return.

Pleae read my link: http://doc.qt.io/qt-5/qpixmap.html#isNull - no setPixmap() but QPixmap::isNull() ...

Stan Huang

@JKSH The return is:
("bmp", "cur", "gif", "ico", "jpeg", "jpg", "pbm", "pgm", "png", "ppm", "xbm", "xpm")

Stan Huang

@Christian-Ehrlicher said in No show of QPixmap:

setPixmap

QPixmap::isNull() returned 'false'

SGaist

What if you set the pixmap directly on the QLabel rather than using a brush in the palette ?

J.Hilk

@Stan-Huang
It's not quite clear from the code you posted, but are you sure that palette_RoadFault is not set to something invalid somewhere else in your code, and that palette_RoadFault persists outside the scope of your function?

QBrush expects a const reference to a QPixmap, I don't think it will take ownership or make a copy of the QPixmap for drawing.

Stan Huang

@SGaist I did it but still doesn't work:
ui->label->setGeometry(20,20,60,20);
ui->label->setPixmap(pixmap_RoadFault);
ui->label->show();

Stan Huang

@SGaist I did but still doesn't work:

				ui->label->setGeometry(20,20,60,20);
				ui->label->setPixmap(pixmap_RoadFault);
				ui->label->show();

SGaist

Don't set the geometry since you have a designer based UI, that will let QLabel in its original place to show the pixmap.

If it's still not working, then test again with another image. And if possible, share that file with us so that we can test it on our ends.

Stan Huang

That's my mistake. A clear statement was executed right after ->show() was executed. That's, show() did its good job, but the shown picture was cleaned immediately. I apologize for my mistake.

JKSH

@Stan-Huang said in No show of QPixmap:

That's my mistake. A clear statement was executed right after ->show() was executed. That's, show() did its good job, but the shown picture was cleaned immediately. I apologize for my mistake.

I'm glad to hear that you've got it working now.

Like I said 10 days ago, it's best to use simple examples. I even wrote a full program for you that works, but you didn't use it.

Stan Huang

@JKSH Yes. I didn't do it 10 days ago due to 9-day lunar new year vacation. Thanks very much.