Qscrollarea does not scroll

[kabanek]

I'm trying to use scrollarea, but I don't get scrollbars.

In my constructor I have

ui->setupUi(this);
Canvas = new JCanvas;
ui->scrollArea->setWidget(Canvas);
Canvas->setGeometry(0, 0, 0, 0);

ui->setupUi(this);
Canvas = new JCanvas;
ui->scrollArea->setWidget(Canvas);
Canvas->setGeometry(0, 0, 0, 0);

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where JCanvas is my implementation of QLabel.

Next, I load a picture and then

QPixmap _image;
_image.load(_fileName);
_image = _image.scaledToWidth(_getSize.PictureWidth);
Canvas->setPixmap(&_image);
//...
qDebug()<<ui->scrollArea->geometry();
qDebug()<<_image.size();

QPixmap _image;
_image.load(_fileName);
_image = _image.scaledToWidth(_getSize.PictureWidth);
Canvas->setPixmap(&_image);
//...
qDebug()<<ui->scrollArea->geometry();
qDebug()<<_image.size();

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in the output for example I got

QRect(11,47 1498x1262)
QSize(1500, 1220)

so size of the pictura is bigger than my qscrollarea.

Here is a screenshot
zrzut ekranu1.jpg

[Lykurg]

Since your scroll area is defined in an ui-file: Are you sure, you set the right scroll bar policies? (See verticalScrollBarPolicy and horizontalScrollBarPolicy)

[kabanek]

I set ScrollBarAsNeeded in both

[wysota]

What does your Canvas implementation look like? Does it have a layout? If not, did you reimplement sizeHint()?

[kabanek]

no and no...

part of JCanvas.h

class JCanvas : public QLabel
{
public:
    JCanvas();
    void paintEvent(QPaintEvent *);
    bool ShowHelpingLines;
    void setPixmap(QPixmap *p);
    void mouseMoveEvent(QMouseEvent *ev);
    void mousePressEvent(QMouseEvent *ev);
    void setLabels(QLabel *labelX, QLabel *labelY);
 
    QStringList cutImages(QString dir);
 
    helpingLines HelpingLines;
    QVector<JSquare> Squares;
    void clearSquares();
 
private:
    QPen Pen;
    QPen PenCut;
    int MouseX, MouseY;
    QPixmap Pixmap;
    QLabel *LabelX, *LabelY;
};

class JCanvas : public QLabel
{
public:
    JCanvas();
    void paintEvent(QPaintEvent *);
    bool ShowHelpingLines;
    void setPixmap(QPixmap *p);
    void mouseMoveEvent(QMouseEvent *ev);
    void mousePressEvent(QMouseEvent *ev);
    void setLabels(QLabel *labelX, QLabel *labelY);

    QStringList cutImages(QString dir);

    helpingLines HelpingLines;
    QVector<JSquare> Squares;
    void clearSquares();

private:
    QPen Pen;
    QPen PenCut;
    int MouseX, MouseY;
    QPixmap Pixmap;
    QLabel *LabelX, *LabelY;
};

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[wysota]

You need to implement sizeHint() properly for your widget to inform its environment about its preferred/required size. QLabel already does that but if you change its behaviour it is likely to return wrong values for what you are doing.

[kabanek]

thanks.

Unfortunately, I don't know how the implementation should look like...

[wysota]

You are the only one who may know it. Only you know what it does and how it does it. We don't.

[ChrisW67]

At a guess your size hint should be the same as the size of the image you load into the JCanvas. Implement QWidget::sizeHint() in your JCanvas and return that size as a starting point. You may also want to try setting QSizePolicy::Fixed on the JCanvas.