How to modify the data in the model and update the view when new data is received from external?

? Offline

@SGaist :I understand tht i need to send dataChanged signal. Where should i update my model? I mean at which place in my code? Secondly for dataChanged i need index values and how would i get it. If you could show me in my code will be helpful. Thankyou

JonB

@VInay123
So when you read the JSON file that's where you will update your model.
For the index values: yes, you have to decide where in your model your data is to go, and from that you will have the index values.

? Offline

@JonB : As you see in my code i read the Json file only ones i..e during initialization with empty values. Later i just want to update the values but not read again the file. Second point how would you suggest me to implement in my design or code? Example would be nice. Thank you.

SGaist

Re-implement setData

? Offline

@SGaist: How would i provide the index values? I am really sorry, because somehow i am not able to understand this trick of updating my data (categories_) in model, i.e. how do i get index from my data and call setData? I would really appreciate if you could show in my code? This would then later emit dataChanged which will achieve my goal.

SGaist

How exactly are you getting new data ?
What are these new data ?
One object update ?
Several objects update ?
How do they fit in your model internal representation ?

? Offline

@SGaist : I am getting this data when user clicks left mouse button. I have slot, so when user clicks button some magic is done and later i save in model member variable Info_.
The NewStructInfo looks like this:
struct NewStructInfo{
double x;
double y;
} Info_;
So now my model data categories_ looks something like this:
```
Property ----------------------------------------- Value
-->Coordinates(categoryitem pointer)
------X (scenariopropertyitem1 pointer type) ------ "Empty"
------Y (scenariopropertyitem pointer type) -------- "Empty"

The above structure you can see in parsejsonobject member function. Now in the above categories_ model data i have iterate along category->secnariopropertyitem and look for the name i,e,

if(scenariopropertyitem->name == x)
// scenariopropertyitem pointer has name as class member
scenariopropertyitem->setValue(QVariant(Info_.X));
Now somehow dataChanged(??,??,Qt::displayrole) has to be called.

SGaist

Since you have to go through your model to find the correct item to update, you should already have the index matching the scenariopropertyitem you found, no ?

? Offline

@SGaist : How would i access it or get the index of the item? Meanwhile would you suggest me to use third option from this answer: https://stackoverflow.com/questions/29921041/getting-the-index-for-a-given-item-in-a-qtreeview-model-application.
Could you provide an example?

? Offline

This post is deleted!

? Offline

This post is deleted!

VRonin

What I always suggest is that if you are not 100% confident in your model design (and, believe me, it's a hard) just use QAbstractItemModel* model = new QStandardItemModel(parent). Then use insertRows, insertColumns, and setData to setup your model

? Offline

In my Model.cpp i did the following:

    emit beginResetModel();
    for (auto& category : categories_) {
        category->entryAt(0)->setValue(1);
        // for testing  i just set randomly my data value to 1
    }
    emit endResetModel();

But after above changes the view is not displaying the new values.

JonB

@VInay123
I don't see any entryAt() function in Qt. So what type is category, what does category->entryAt(0)->setValue(1) do in the way of setting anything in the model??

? Offline

@JonB: If you see my code Category is a class which has entryAt() function which returns back the propertyitem. So here i am setting the model data i.e. my categories_ member variable in the model class.

JonB

@VInay123
OK for entryAt(). But where in your code does entryAt(0)->setValue(1) call QAbstractModel::setData() (http://doc.qt.io/qt-5/qabstractitemmodel.html#setData)? Where is the http://doc.qt.io/qt-5/qabstractitemmodel.html#dataChanged signal being emitted?

? Offline

@JonB: That is the problem i am facing. I do not know how to call setData which in turn emits the signal dataChanged. I do not know how to get the indexes. Here the data is only coming from the "Info_" variable. If the it was via delegates or adapters i could easily get the indexes and call setData. But in my case i get in a structure and go through each item and update its value. Could you please show me how can i achieve this in my code i.e. change the value via setData?

JonB

@VInay123
Your code is way too big for me to wade through.

If you are using QAbstractModel, you are using a model which holds data in rows & columns, right?
When you put some data (received from JSON parsing or whatever), you have to decide where in the model's row/column you want to put this data, right?
Given that row & column, you can construct a QModelIndex() (http://doc.qt.io/qt-5/qabstractitemmodel.html#createIndex) for the data.
Then you can pass that to your Model::setData() to set the value, and emit dataChanged(index, index) to notify your view to update.

? Offline

@JonB : Thank you. I implemented as following in my model:

    QModelIndex index = createIndex(1, 1, categories_[0]->entryAt(0));
    this->setData(index, 11, Qt::EditRole);

It is changing the value clearly. But in the view its not being displayed.

JonB

@VInay123
Well at least we're getting somewhere! Check the return result of your setData(), maybe it's failing? Does (row, column) of (1, 1) exist in your model (else you need to insertRows() etc.)? Is that setData() call indeed going into your Model::setData() and doing the emit dataChanged() there (use a debugger or debug/print statements)? There's no point using both beginResetModel() & dataChanged(), and certainly not dataChanged() while still inside the beginResetModel() before the nedRestModel(). Change your code accordingly.