Need help to create simple model for QTreeModelView

mrjj

Hi
Ran your code.
You dont have any items ?
I dont see you add anything to the list and it also reports zero

alt text

Ah you do add one here


void MyModel::fetchRootDirectory()
{
    _items.push_back(new MyItem("first_item"));
}

so the rowCount code seems not correct.

Please_Help_me_D

@JonB thank you for reply
Yes I saw this. It is opened in my editor but I still don't understand why I cannot run mine
@mrjj yes, I add item in fetchRootDirectory

mrjj

@Please_Help_me_D
But when view ask how many items you got via rowCount, you return zero.
as in No rows and that is what you see.

Please_Help_me_D

@mrjj Why do I return zero?
Are the comments below are true?

int MyModel::rowCount(const QModelIndex &parent) const
{
    if (!parent.isValid()) { // if this is  a root (there is no parent)
        return _items.size(); // this returns 1 and the application goes here
    }
    const MyItem* parentItem = static_cast<const MyItem*>(parent.internalPointer()); // 

    return parentItem->children.size(); //returns zero but the application never reach there
}

Please_Help_me_D

@Please_Help_me_D Oh no, I'm wrong...

mrjj

@Please_Help_me_D
well
you return parentItem->children.size()
and that is zero as it has no children :)

So not sure if this is a tree or list or table model ?

Please_Help_me_D

@mrjj it should be tree model

mrjj

@Please_Help_me_D
Then you should add more than the first item :)
So the root item does have children.

Please_Help_me_D

@mrjj Well I add few children to item:

void MyModel::fetchRootDirectory()
{
    MyItem* item = new MyItem("first_item");
    item->children.push_back(new MyItem("first_child"));
    item->children.push_back(new MyItem("second_child"));
    _items.push_back(item);
}

but it still doesn't work :)

mrjj

@Please_Help_me_D
so check with debugger what you return as rowCount ?

Please_Help_me_D

@mrjj I wrote:

int MyModel::rowCount(const QModelIndex &parent) const
{
    if (!parent.isValid()) {
        qDebug() << "Item size: " << _items.size();
        return _items.size();
    }
    const MyItem* parentItem = static_cast<const MyItem*>(parent.internalPointer());
    qDebug() << "Children size: "  << parentItem->children.size();
    return parentItem->children.size();
}

The output is:

Item size:  1
Item size:  1
Item size:  1
Item size:  1
Item size:  1
Item size:  1
Item size:  1
Item size:  1
Item size:  1
Item size:  1
Item size:  1
Item size:  1
Children size:  2
Item size:  1
Item size:  1
Item size:  1
Item size:  1
Item size:  1
Item size:  1
Children size:  2
Item size:  1
Item size:  1
Item size:  1

Why the program goes to rowCount so many times? I already suspected that when I set the breakpoint and tried to contue application run to next breakpoint. Is it normal?

JonB

@Please_Help_me_D said in Need help to create simple model for QTreeModelView:

Why it gives me such many outputs?

Because your rowCount() gets called by Qt (e.g. the QTreeView) more times than you think it does :)

Please_Help_me_D

@JonB and is it normal? or my code looks so scarry that Qt don't know what to do whith it :)

Please_Help_me_D

@mrjj maybe I should manually insert rows somehow?

mrjj

Hi
Im not sure what is wrong as could also be the index but you can take a look at
https://doc.qt.io/qt-5/qtwidgets-itemviews-editabletreemodel-example.html
which seems very similar to your code.

Please_Help_me_D

@mrjj ok
How do you think, is it possible that the problem is how I declare variables (pointers/references and const)?. Sometimes they differ from examples but I think it should be fine

mrjj

@Please_Help_me_D
well i think its fine since app compiles etc.
Its more that if you use internalPointer as in the example so it does point to what you expect.

JonB

@Please_Help_me_D said in Need help to create simple model for QTreeModelView:

@JonB and is it normal? or my code looks so scarry that Qt don't know what to do whith it :)

No, it's normal that infrastructure will call your rowCount() a lot :)

Please_Help_me_D

@mrjj @JonB well guess what? Yes I've found the snippet of code that made me feel useless for whole day :D
Previously I had the MyModel::data() method:

QVariant MyModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid()) {
        return QVariant();
    }
    
    const MyItem* item = static_cast<MyItem*>(index.internalPointer());
    return item->title;
}

But when I change it to:

QVariant MyModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid()) {
        return QVariant();
    }

    if (role != Qt::DisplayRole && role != Qt::EditRole)
        return QVariant();

    const MyItem* item = static_cast<MyItem*>(index.internalPointer());
    return item->title;
}

everything works :)
Now I'm trying to understand what the role is
Thank you for help!

mrjj

@Please_Help_me_D said in Need help to create simple model for QTreeModelView:

that made me feel useless for whole day

Ehh, should it not make you feel happy you found it ?

So good spotted.

The roles are explained here
https://doc.qt.io/qt-5/qt.html#ItemDataRole-enum