regarding role in setData method of QAbstractItemModel

Qt Enthusiast

I have a function in which I show a image in first column of each row . I return a QIcon in ::data . My requirement is to edit the image when I double click on this image

class myView : public QTreeView{
private:
myModel d_m;
};

class myModel:public QAbstractItemmodel
};

myView::myview() {
myModel m;
setModel(m);
d_m =m;
}

void myInstView::clickInstance(const QModelIndex& index)
{
d_m->setData(setData(currentIndex(),color,Qt::DecorationRole);;
}

boo myModel::setData(const QModelIndex& index,const QVariant& variant, const int role)
{
if (role == Qt::DecorationRole && index.column() == 1) {
QColor color = variant.value<QColor>();
myMap[pointer] = image;
addIamgeToMap(image);
/* set color for all the visible children
}
}

QVariant myModel::data(const QModelIndex& index, int role) const
{
if(index.coumn ==1) && role== Decoration role {
return myMap[pointer] ;
}
}

My Query is is sending Decoration in setData is fine and is the logic is also fine ?

VRonin

Doing this kind of things is exactly what delegates are made for. take a look at http://doc.qt.io/qt-5/model-view-programming.html#delegate-classes and QStyledItemDelegate

Qt Enthusiast

I took help from this example

http://doc.qt.io/qt-5/qtwidgets-itemviews-editabletreemodel-example.html

what is the problem in my code

VRonin

@Qt-Enthusiast said:

I have a function in which I show a image in first column of each row

you are checking for index.coumn()==1 so that's the second column

class myView : public QTreeView{
private:
myModel d_m;
};

Usually it's not a great idea to make the view own the model. you can do it (that's what the Q*Widgets do) but it's often not the best way

class myModel:public QAbstractItemmodel
};

myView::myview() {
myModel m;
setModel(m);
d_m =m;

how can you do this? QObjects can't be copied also the logic here is wrong as you store a copy of the model but then use the original one as base for the view

void myInstView::clickInstance(const QModelIndex& index)

what is myInstView?

 return myMap[pointer] ;

What is pointer?

the logic is also fine ?

using the decoration role to display the image is 100% correct but to edit the image you should use a delegate

Qt Enthusiast

I am using qt.4.3.3 and qstyleditemdelegate.html is available fro,m qt4.4 so I cannot used qstyleditemdelegat please let me know if I impilimentation is ok

VRonin

you can use QItemDelegate, the only difference is that QStyledItemDelegate uses stylesheets while QItemDelegate doesn't http://doc.qt.io/qt-4.8/qitemdelegate.html

Qt Enthusiast

can u point me exact example where QtreeView , customodel and a deletegate is used so that I understand the things better

Since storing a model pointer in View is my legacy code can I call

class myView::QTreeView {
}

void myView::clicik() {
d_m->setData
}

VRonin

create a class that inherits from QItemDelegate and reimplement

virtual QWidget* createEditor(QWidget * parent, const QStyleOptionViewItem & option, const QModelIndex & index) const;
virtual void setEditorData(QWidget * editor, const QModelIndex & index) const;
virtual void setModelData(QWidget * editor, QAbstractItemModel * model, const QModelIndex & index) const;
virtual QSize sizeHint(const QStyleOptionViewItem & option, const QModelIndex & index) const;
virtual void updateEditorGeometry(QWidget * editor, const QStyleOptionViewItem & option, const QModelIndex & index) const;

the widget returned from createEditor is displayed inside the view cell during editing, setEditorData is used to load data from the model to the editor, setModelData is used to save data from the editor to the model.

updateEditorGeometry is used to resize the editor in case the view gets resized during editing and sizeHint tells the view how much space your image should take

finally you use QTreeView::setItemDelegateForColumn to set the delegate on the view and voilà

you can use QTreeView::setEditTriggers to chose when your editor should pop up ( QAbstractItemView::DoubleClicked I think in your case)

Qt Enthusiast

My question is what is advantage of using delegate since my legacy code my View owns the model pointer

is there any advandathe

VRonin

not knowing what myInstView is I can't provide a definitive answer but handling your editor widget lifetime, positioning it correctly, resizing it correctly and handling when the editing starts and finishes all out of the box are pretty big advantages for me

Qt Enthusiast

it is a object of QTreeVIew

VRonin

That's not particularly helpful... what class is it? a button? a lineedit?

Qt Enthusiast

a QTreeView

VRonin

I don't get the difference between myInstView and myView but it does not matter. Delegate is the answer.

My requirement is to edit the image when I double click on this image

if you want any more details you need to describe better how the image should be changed. is it selected from a combobox, is it a color button, is it loaded from file?