Solved 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();