Draw a PE_IndicatorBranch in a QLabel

oberluz

Hi,

I'm trying to customise a QlistView row by having the first item in each row show an indicator branch such as that used in QTreeView.

To accomplish this I add the following widget as the first item in each row. The label text is displayed correctly but I cannot get the indicator branch to display.

I can get other primitive elements (eg down arrow) to display but not the indicator branch.

Any ideas?

    class NodeWidget : public QLabel
    {
    public:
        NodeWidget(QWidget *parent = nullptr) :
            QLabel("this text is displayed", parent)
        {
        }

    private:
         void paintEvent(QPaintEvent *);
    };

    void NodeWidget::paintEvent(QPaintEvent *e)
    {
        QLabel::paintEvent(e);
        QPainter painter(this);

        QStyleOptionFocusRect option;
        option.initFrom(this);
        option.backgroundColor = palette().color(QPalette::Background);
        option.state = QStyle::State_Item | QStyle::State_Children;
        style()->drawPrimitive(QStyle::PE_IndicatorBranch, &option, &painter, this);
    }

mrjj

Hi
I think it needs a rect also, but not sure its the only thing.

class NodeWidget : public QLabel
{
public:
    NodeWidget(QWidget *parent = nullptr) :
        QLabel("this text is displayed", parent) { }
private:
    void paintEvent(QPaintEvent *e)
    {
        
        QLabel::paintEvent(e);
        
        QStyleOption branchOption;
        QPainter painter(this);
        //painter.setBrush( Qt::white);
        //painter.drawRect(0, 0, width() - 1, height() - 1);
        branchOption.initFrom(this);
        branchOption.state = QStyle::State_Item | QStyle::State_Children;
        //  branchOption.state |= QStyle::State_Open; // if to draw open
        branchOption.rect = rect();// adjust this
        style()->drawPrimitive(QStyle::PE_IndicatorBranch, &branchOption, &painter, this);

    }
};

alt text

oberluz

@mrjj thanks

When I read you reply I was in fact playing around setting the option.rect which you correctly identified as not having been sent, although I still haven't been able to display the indicator branch.

I think it may have to do with the fact that the label is within a layout in a QListwidget row item. Just assigning the QLabel rect doesn't seem enough in my case.

I'll keep on trying...

mrjj

@oberluz
Hi
well if you look at the test code, it seems that
style()->drawPrimitive(QStyle::PE_IndicatorBranch draws the
the indicator in the center of the rect given.
It should not matter if inside a QListwidget but you might want to
check the rect label.

oberluz

@mrjj Yes I noticed that. I've replicated your test example and I can now get it to display in the row of a QListWidget. Thanks

mrjj

@oberluz
You can simply calculate a new rect for the beginning of the text line and
then ask QLabel to center text or similar.
If you want complete control you should draw both text and PE_IndicatorBranch
with painter.
(and not call QLabel::paintEvent(e); )
However, if you use rich text in Label or mutliple lines it is slightly more complicated.

oberluz

@mrjj thanks. I was able to get it to work if the QListWidget was the central widget in the QApplicaiton as per your example. However if I add it to a dock widget they fail to draw:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

    QWidget* createListWidget();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

#include "MainWindow.h"
#include "ui_MainWindow.h"
#include <QListWidget>
#include <QLabel>
#include <QPainter>
#include <QHBoxLayout>
#include <QApplication>
#include <iostream>
#include <QDockWidget>

class NodeWidget : public QLabel
{
public:
    NodeWidget(QWidget *parent = NULL) :
        QLabel("", parent)
    {
    }

private:
     void paintEvent(QPaintEvent *);
};

void NodeWidget::paintEvent(QPaintEvent *e)
{
    QLabel::paintEvent(e);
    QPainter painter(this);
    QStyleOption option;
    option.initFrom(this);
    option.rect = rect();
    option.state = QStyle::State_Item | QStyle::State_Children;
    style()->drawPrimitive(QStyle::PE_IndicatorBranch, &option, &painter, this);
}

class RowWidget : public QWidget
{
public:
    RowWidget(const QString& text, QWidget *parent = NULL);
};


RowWidget::RowWidget(const QString &text, QWidget *parent) :
    QWidget(parent)
{
    QHBoxLayout* layout = new QHBoxLayout(this);
    layout->setContentsMargins(0,0,0,0);

    layout->addWidget(new NodeWidget(this));
    layout->addWidget(new QLabel(text, this));
    layout->addWidget(new QLabel("text", this));

    setLayout(layout);
}


MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    layout()->setContentsMargins(0,0,0,0);

    QString styleSheet("QDockWidget::title { font: 75 11pt \"ubuntu\"; text-align: left; background: darkgray; }");

    QDockWidget* m_dockWidget;
    m_dockWidget = new QDockWidget(" Dock Window", this);
    m_dockWidget->setObjectName(QString::fromUtf8("DockWidget"));
    QSizePolicy sizePolicy6(QSizePolicy::Minimum, QSizePolicy::Minimum);
    sizePolicy6.setHorizontalStretch(0);
    sizePolicy6.setVerticalStretch(0);
    sizePolicy6.setHeightForWidth(m_dockWidget->sizePolicy().hasHeightForWidth());
    m_dockWidget->setSizePolicy(sizePolicy6);
    m_dockWidget->setAllowedAreas(Qt::LeftDockWidgetArea|Qt::RightDockWidgetArea|Qt::TopDockWidgetArea|Qt::BottomDockWidgetArea);

    m_dockWidget->layout()->setContentsMargins(0,0,0,0);
    m_dockWidget->setStyleSheet(styleSheet);

    addDockWidget(Qt::BottomDockWidgetArea, m_dockWidget);

    QWidget* list = createListWidget();
    m_dockWidget->setWidget(list);

    {
        QWidget* list = createListWidget();
        setCentralWidget(list);
    }
}

MainWindow::~MainWindow()
{
    delete ui;
}

QWidget *MainWindow::createListWidget()
{
    QListWidget* list = new QListWidget(this);
    list->setAlternatingRowColors(true);

    RowWidget* widget = new RowWidget("one", list);
    QListWidgetItem* item = new QListWidgetItem(list);
    item->setSizeHint(widget->minimumSizeHint());
    list->addItem(item);
    list->setItemWidget(item, widget);

    widget = new RowWidget("two", list);
    item = new QListWidgetItem(list);
    item->setSizeHint(widget->minimumSizeHint());
    list->addItem(item);
    list->setItemWidget(item, widget);

    widget = new RowWidget("three", list);
    item = new QListWidgetItem(list);
    item->setSizeHint(widget->minimumSizeHint());
    list->addItem(item);
    list->setItemWidget(item, widget);

    return list;
}

oberluz

@oberluz said in Draw a PE_IndicatorBranch in a QLabel:

drawPrimitive

my bad: the style sheet is causing the issue. Can't see why that could cause it?

mrjj

Hi
What does the stylesheet target?
margins and such can affect lots of stuff if not
target using names or concrete types as selectors

oberluz

@mrjj I only intended it to darken the dock window title bar:

QString styleSheet("QDockWidget::title { font: 75 11pt \"ubuntu\"; text-align: left; background: darkgray; }");

mrjj

@oberluz
so if you do use styleSheet it looks as you expect?
you are right, im not sure either how that should affect NodeWidget

oberluz

@mrjj yes, without the stylesheet its fine:

Is its possible I need to get the current style sheet, then somehow add the title, and then set it ? I'm thinking that by just setting it rather than modifying it I might be deleting something

mrjj

@oberluz
Hi
Unless you manually set a stylesheet, its empty pr default.
so if that is the ONLY stylesheet you set, i dont get it.

oberluz

@mrjj its the only one, the example I posted is complete

mrjj

@oberluz
Sorry, i really cant guess.
It seems not very connected.
and should only affect Title

oberluz

@mrjj Maybe a bug.. I might raise one with this example

mrjj

@oberluz
Could be.
Please make a small sample that can reproduce it.
Makes it far more likely we discover what it is. :)

oberluz

@mrjj will do and I'll run it under 5.13 before submititng

mrjj

@oberluz
Super.
and please post link to bug here :)

oberluz

@mrjj https://bugreports.qt.io/browse/QTBUG-76947
as promised. reproduced it with 5.13.