I got it wrong, can't compile

[been_1990]

I tried following the MVF video but wasnt able to get what I wrote down to compile:

main.cpp

#include <QtGui/QApplication>
#include "delegate.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    //Widget w;
    //w.show();
    ListDelegate *delegate;
    QListView view;
    view.setItemDelegate(delegate);
    view.show();
    return a.exec();
}

#include <QtGui/QApplication>
#include "delegate.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    //Widget w;
    //w.show();
    ListDelegate *delegate;
    QListView view;
    view.setItemDelegate(delegate);
    view.show();
    return a.exec();
}

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delegate.h

#ifndef DELEGATE_H
#define DELEGATE_H
#include <QtGui>
 
class ListDelegate : public QAbstractItemDelegate
{
public:
    ListDelegate(QObject *parent=0);
 
    void paint(QPainter *painter,
               const QStyleOptionViewItem &option,
               const QModelIndex &index) const;
 
    QSize sizeHint(const QStyleOptionViewItem &option,
                   const QModelIndex &index)const;
};
 
QSize ListDelegate::sizeHint(const QStyleOptionViewItem &option,
               const QModelIndex &index) const
{
    return QSize(100,40);
}
 
void ListDelegate::paint(QPainter *painter,
           const QStyleOptionViewItem &option,
           const QModelIndex &index) const
{
    QColor background;
 
    if(option.state & QStyle::State_Selected)
        background = Qt::darkRed;
    else
        background = Qt::lightGray;
 
    painter->setFont(QFont("Arial",12,QFont::Bold));
    painter->drawText(option.rect, Qt::AlignCenter,
                      index.model()->data(index).toString());
}
#endif // DELEGATE_H

#ifndef DELEGATE_H
#define DELEGATE_H
#include <QtGui>

class ListDelegate : public QAbstractItemDelegate
{
public:
    ListDelegate(QObject *parent=0);

    void paint(QPainter *painter,
               const QStyleOptionViewItem &option,
               const QModelIndex &index) const;

    QSize sizeHint(const QStyleOptionViewItem &option,
                   const QModelIndex &index)const;
};

QSize ListDelegate::sizeHint(const QStyleOptionViewItem &option,
               const QModelIndex &index) const
{
    return QSize(100,40);
}

void ListDelegate::paint(QPainter *painter,
           const QStyleOptionViewItem &option,
           const QModelIndex &index) const
{
    QColor background;

    if(option.state & QStyle::State_Selected)
        background = Qt::darkRed;
    else
        background = Qt::lightGray;

    painter->setFont(QFont("Arial",12,QFont::Bold));
    painter->drawText(option.rect, Qt::AlignCenter,
                      index.model()->data(index).toString());
}
#endif // DELEGATE_H

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[wysota]

What is the error you get? By the way, this code won't work as you are using an uninitialized variable in main().

[been_1990]

What "uninitialized variable in main()"? The program just stops working, crashes.

[wysota]

So why did you say you were unable to compile the application? Compilation error and crashing are two different things.

Your "delegate" variable is uninitialized. It's just a place in memory pointing to some garbage.

I suggest you polish your C++ skills a bit.

[been_1990]

Sorry about it, terrible mistake. I confused myself.
About the uninitialized variable, this is how the ICS video wrote the code:

ListDelegate delegate;
    QListView view;
    view.setItemDelegate(&delegate);
    view.show();

ListDelegate delegate;
    QListView view;
    view.setItemDelegate(&delegate);
    view.show();

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Which does not compile and outputs:

F:\Documents\QT Projects\QListView_test/main.cpp:8: undefined reference to `ListDelegate::ListDelegate(QObject*)'
:-1: error: collect2: ld returned 1 exit status

F:\Documents\QT Projects\QListView_test/main.cpp:8: undefined reference to `ListDelegate::ListDelegate(QObject*)'
:-1: error: collect2: ld returned 1 exit status

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And the ListDelegate class is written exactly as the video. But you are definitely right about my C++ skills...

[wysota]

You didn't implement the constructor for the ListDelegate class.

[been_1990]

How do I implement it? I thought that ListDelegate(QObject *parent=0);was the constructor for the ListDelegate class.

[wysota]

How do I implement it? I thought that ListDelegate(QObject *parent=0);was the constructor for the ListDelegate class.

Come on, man. It's a declaration of the constructor. Where is its body?

[been_1990]

Don't kill me for asking, but how do I implement it? The video didn't write anything else, the source code, QAbstractItemDelegate.cpp the body of the constructor is blank , it's just like that:

QAbstractItemDelegate::QAbstractItemDelegate(QObject *parent = 0)
{
 
}

QAbstractItemDelegate::QAbstractItemDelegate(QObject *parent = 0)
{

}

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And now when I try to compile I get this other error:

F:/Documents/QT Projects/QListView_test/main.cpp:10: error: no matching function for call to 'QListView::setItemDelegate(ListDelegate&)'
c:\Qt\2009.05\qt\include\QtGui/../../src/gui/itemviews/qabstractitemview.h:135: note: candidates are: void QAbstractItemView::setItemDelegate(QAbstractItemDelegate*)

F:/Documents/QT Projects/QListView_test/main.cpp:10: error: no matching function for call to 'QListView::setItemDelegate(ListDelegate&)'
c:\Qt\2009.05\qt\include\QtGui/../../src/gui/itemviews/qabstractitemview.h:135: note: candidates are: void QAbstractItemView::setItemDelegate(QAbstractItemDelegate*)

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Im trying to understand, doing my best. Thanks for your help.

[wysota]

http://www.mindview.net/Books/TICPP/...ngInCPP2e.html

[been_1990]

For some unknown reason it compiled and now runs perfectly. With main :

ListDelegate delegate;
 
QListView view;
 
view.setItemDelegate(&delegate);
 
view.show();

ListDelegate delegate;

QListView view;

view.setItemDelegate(&delegate);

view.show();

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And ListDelegate constructor:

ListDelegate::ListDelegate(QObject *parent = 0)
{
 
}

ListDelegate::ListDelegate(QObject *parent = 0)
{
 
}

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I still am clueless as to why. I read the pixelator example on QT, and it's custom delegate class constructor is the same as mine, empty.
Now if I try to use a custom QAbstractListModel I get the same issues as I previously had with QAbstractItemDelegate.

[wysota]

The unknown reason is that you added the body of the constructor.

[been_1990]

Ok. Thanks for your help.