QTreeView with Model-View help

[MathStuf]

Hi,

I am trying to make a tree for my data objects, but I am having trouble figuring out how I should approach it to make it as clean as possible. I was using a QTreeWidget, but it felt very hackish and wasn't very nice to keep up with. I'd like to use a QTreeView, but I am unsure of how to handle the models. An example of how my data classes work is below.

• data class 1
  
  • group
    
    • sub-data class 1
      
      • group
        
        • sub-sub-data class 1
  • group
  • group
• data class 2
  
  • group
  • group
  • group

At the root, there are the large data classes, then there are groups of related data classes within that (the groups keep unrelated data classes from grouping together). When a data class is added, it needs to build its subtree of data and groups. the group "labels" cant be selected, but the data classes each have a widget for editing the internal data. How should I design the model to handle this?

--MathStuf

Edit: Typoed QList* rather than QTree*

[wysota]

Shouldn't you be using QTreeView and not QListView?

[MathStuf]

Wow, that's a typo. I'll edit to fix that.

--MathStuf

[wysota]

How should I design the model to handle this?

Could you explain what do you mean by the word "how" here? The question is very general, so it's hard to provide a detailed answer to your question.

[MathStuf]

I would like to know how I could got the model to handle the different types of data classes without being a huge if else tree. If that's the only way, I'll make it work, but I was wondering if something like template or subclassing could work here. I'm not sure how the internals of the model-view work and if that would work at all.

--MathStuf

[wysota]

I'd go for subclassing. Make your elements derived from a common base class with virtual methods and delegate the model's methods to items using virtual methods.

[MathStuf]

All of my data classes are derived from a common base class. Not all of the data classes have the same getter/setter methods, so there are different widgets for each, again which are derived from a common base class.

If you mean subclassing the models for each data class , how would i get the QTreeView to use a different model depending on the item type? If I'm misinterpreting what you're saying, let me know.

I think one of the places I keep tripping over is how to figure out is how to keep the grouping entries from getting confused with the data entries. I wish that this would just straighten itself out in my mind like the rest of the "how should I do this?" problems have with this project.

--Ben

[wysota]

I mean exactly what I wrote Provide a common interface for all types of objects your tree carries and use the interface from within the model. For instance:

class Base {
public:
  QVariant data(int role=Qt::DisplayRole) const = 0;
};
 
class Level1Item : public Base {
public:
  QVariant data(int role=Qt::DisplayRole) const {
    return myName;
  }
};
 
QVariant Model::data(const QModelIndex &index, int role){
  if(!index.isValid()) return QVariant();
  Base *ptr = static_cast<Base*>(index.internalPointer());
  return ptr->data(role);
}

class Base {
public:
  QVariant data(int role=Qt::DisplayRole) const = 0;
};

class Level1Item : public Base {
public:
  QVariant data(int role=Qt::DisplayRole) const {
    return myName;
  }
};

QVariant Model::data(const QModelIndex &index, int role){
  if(!index.isValid()) return QVariant();
  Base *ptr = static_cast<Base*>(index.internalPointer());
  return ptr->data(role);
}

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[MathStuf]

Oh, ok. I see what you mean now. Thanks a lot.

--MathStuf

[MathStuf]

I have another question with this. Each model can change the number of children rows from within (i.e. the Level1Item class above) with setData. Do I have to signal beginRemoveRows/beginInsertRows and their end equivalent?

--MathStuf

[wysota]

Yes, you have to emit some signals. Emitting layoutChanged() or even reset() might be an option instead of using begin/end*Rows.