loadPixmap returns true but does not display/show on-screen

[Halordain]

Hi,

I extended QGraphicsView and, in its constructor, want to load a few pixmaps to display on-screen. To test that the pixmaps are properly loaded, I use qWarning (see below), and from what I can tell in the watch window locals, the image is being loaded. However, past that point, I don't know how to check the data in QLabel if it isn't showing up properly on screen. QLabels are loaded into QGraphicsGridLayout, which is then setLayout into the top-level QGraphicsObject:

MyViewer::MyViewer(QGraphicsScene *scene)
{
 
    QGraphicsGridLayout *layout = new QGraphicsGridLayout;
    img_board.resize(8);
    for (int i = 0; i < 8; ++i)
        img_board[i].resize(8);
    for (int j = 0; j < 8; ++j) {
        for (int i = 0; i < 8; ++i) {
            int index = 8*i + j;
            char buffer[200];
            QString qindex = itoa(index, buffer, 10);
            QString filename(qApp->applicationDirPath() + "/img/");
            filename += qindex;
            filename += ".png";
 
            QPixmap qimg;
            if (qimg.load(filename))
                qWarning("Failed to load target image");
 
            img_board[j][i] = new QLabel;
            img_board[j][i]->setPixmap(qimg);
            QGraphicsProxyWidget* pixwidget = scene->addWidget(img_board[j][i]);
            layout->addItem(pixwidget, i, j + 1);
        }
    }
    QGraphicsWidget* form = new QGraphicsWidget;
    form->setLayout(layout);
    scene->addItem(form);
    setWindowTitle(tr("TESTING"));
    resize(800, 600);
    form->show();
}
 
.....
 
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QGraphicsScene* scene = new QGraphicsScene;
    MyViewer window(scene);
    window.show();
    return app.exec();
}

MyViewer::MyViewer(QGraphicsScene *scene)
{
  
    QGraphicsGridLayout *layout = new QGraphicsGridLayout;
    img_board.resize(8);
    for (int i = 0; i < 8; ++i)
        img_board[i].resize(8);
    for (int j = 0; j < 8; ++j) {
        for (int i = 0; i < 8; ++i) {
            int index = 8*i + j;
            char buffer[200];
            QString qindex = itoa(index, buffer, 10);
            QString filename(qApp->applicationDirPath() + "/img/");
            filename += qindex;
            filename += ".png";

            QPixmap qimg;
            if (qimg.load(filename))
                qWarning("Failed to load target image");

            img_board[j][i] = new QLabel;
            img_board[j][i]->setPixmap(qimg);
            QGraphicsProxyWidget* pixwidget = scene->addWidget(img_board[j][i]);
            layout->addItem(pixwidget, i, j + 1);
        }
    }
    QGraphicsWidget* form = new QGraphicsWidget;
    form->setLayout(layout);
    scene->addItem(form);
    setWindowTitle(tr("TESTING"));
    resize(800, 600);
    form->show();
}

.....


int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QGraphicsScene* scene = new QGraphicsScene;
    MyViewer window(scene);
    window.show();
    return app.exec();
}

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The application builds and runs, but the window is just one large white box. I tried digging into img_board as well as layout in the debugger, but the values are a bunch of addresses, with nothing I can use to verify that I properly loaded the pixmap. However, the warnings have stopped, so loads are working, I think.

Thanks for your help!

[high_flyer]

From QPixmap doc:

Returns true if the pixmap was successfully loaded; otherwise returns false.

QPixmap qimg;
            if (qimg.load(filename)) //if this warning is NOT printed, it means the image is NOT loaded - you need to add '!' to the if statement.
                qWarning("Failed to load target image");

QPixmap qimg;
            if (qimg.load(filename)) //if this warning is NOT printed, it means the image is NOT loaded - you need to add '!' to the if statement.
                qWarning("Failed to load target image");

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you should also test against isNull(), to be on the safe side.

[Halordain]

Thank you! I changed it, changed my pathname, and got it to build without any warning messages....... but nothing shows up.

QString qindex = itoa(index, buffer, 10);
            QString filename("img/");
            filename += qindex;
            filename += ".png";
 
if (!qimg.load(filename))
                qWarning("Failed to load target image");
 if (qimg.isNull())
                qWarning("Failed to load target image");
 
            img_board[j][i] = new QLabel;
            img_board[j][i]->setPixmap(qimg);
 
            if (img_board[j][i] == NULL)
                qWarning("Failed to load target image");

QString qindex = itoa(index, buffer, 10);
            QString filename("img/");
            filename += qindex;
            filename += ".png";

if (!qimg.load(filename))
                qWarning("Failed to load target image");
 if (qimg.isNull())
                qWarning("Failed to load target image");

            img_board[j][i] = new QLabel;
            img_board[j][i]->setPixmap(qimg);

            if (img_board[j][i] == NULL)
                qWarning("Failed to load target image");

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...where, in the .h file, I define...

vector<vector<QLabel*> > img_board;

vector<vector<QLabel*> > img_board;

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Compile message is

Starting C:\Qt\qt\examples\widgets\tetrix-build-desktop\debug\tetrix.exe...
BLANK WINDOW APPEARS
I close it...
C:\Qt\qt\examples\widgets\tetrix-build-desktop\debug\tetrix.exe exited with code 0

[high_flyer]

Try calling setVisible() on your proxy widgets.