I'm still struggling with model/view

[mzimmers]

No, I didn't copy the example yet...I actually started this application before being introduced to model/view. I'm now trying to retrofit whatever makes the most sense.

In looking at the books example, I'm struck by the automation that the classes provide. I don't think there's a single instance of a "connect" command in the source code, for example. This is impressive, but it's also hard to use as an example. I'm reading the (long) page on Qt model/view and hope that will help out a bit.

Edit: correction: there is indeed one connect. Still pretty impressive.

[mrjj]

@mzimmers
Well the tablemodel class handles most of that internally and the views already automatically connect to
the signals they need from model.
You should be able to directly use tablemodel.cpp/.h and
only replace Contact with your struct and fix the places where its members are used.
Then it should be working with no extra code.

Its a good idea to read the docs on this topic. Model & Views are a bit involved but
also provides many benefits.

[VRonin]

Subclassing models is a minefield. That's why I suggested using QStandardItemModel instead. The idea was that you can store

struct DeviceDetails
{
    QString macAddr;
    QString devName;
    QString latestTimestamp;
};

as:

enum DeviceRoles{
macAddr = Qt::UserRole
, devName
, latestTimestamp
};
auto item = new QStandardItem;
item->setData(/*...*/,DeviceRoles::macAddr);
item->setData(/*...*/,DeviceRoles::devName);
item->setData(/*...*/,DeviceRoles::latestTimestamp);
myModel.appendRow(item);

The model subclass is probably the most correct way but before embarking into it, please read the chapter of Advanced Qt programming I linked in the previous thread and run your custom model through the Model Test

P.S.
Allocating QStandardItem on the stack is problematic. QStandardItemModel will take ownership of the item and try to delete it. That means that if you declare the item before the model

QStandardItem myItem;
QStandardItemModel myModel;

You'll get a crash as well as if you try to remove that row you'll get a crash

[mzimmers]

@VRonin OK, that makes a lot more sense. So, is the missing field in your setData() examples a pointer to my structure element? Is that how the model keeps track of changes to that data?

[VRonin]

No, my example was using QStandardItemModel. the missing argument is the actual value you want to save in the model, something like item->setData(QStringLiteral("00:A0:C9:14:C8:29"),DeviceRoles::macAddr);

[mzimmers]

Oh, I see. So, am I then responsible for manually updating the item when data changes?

[VRonin]

@mzimmers said in I'm still struggling with model/view:

am I then responsible for manually updating the item when data changes?

Correct, but that would always be the case. if you subclass QAbstractItemModel it's your responsibility to signal changes of data emitting the dataChanged signal

[mzimmers]

So, if I understand this, the general program flow would be:

1. the worker thread receives updates from the various devices
2. the worker passes the updates (via a signal) to the model
3. the model then either adds rows or modifies existing rows
4. the UI automatically reflects the change to the model.

That about right?

One thing I'm still not clear on, is how to modify data in existing rows, for example, changing the timestamp on a device that's already been added.

[VRonin]

@mzimmers said in I'm still struggling with model/view:

That about right?

What workflow did you decide to adopt?

• Use QStandardItemModel
• or subclass QAbstractItemModel

[mzimmers]

I'm now trying to use QStandardItemModel. Unfortunately, the data isn't showing up in the QTableView yet, so I'll have to work through to see where it's failing.

[VRonin]

I'm now trying to use QStandardItemModel

Then:

1. the worker thread receives updates from the various devices
2. the worker passes the updates (via a signal) to a QObject in the main thread that owns the model
3. the object inserts/removes/updates the model
4. the UI automatically reflects the change to the model.

[mzimmers]

Yes, that's how I'm doing it. (My model class is DeviceModel.) Just as a test, I put this into the c'tor:

DeviceModel::DeviceModel()
{
    QString s1 = "aaa", s2 = "bbb", s3 = "ccc";
    QVariant qv;

    qv = s1;
    item.setData(qv, DeviceRoles::macAddr);
    qv = s2;
    item.setData(qv, DeviceRoles::devName);
    qv = s3;
    item.setData(qv, DeviceRoles::latestTimestamp);
    appendRow(&item);
}

I'd expect to see this in my QTableView, but I don't. What might I be missing?

[VRonin]

I'm now trying to use QStandardItemModel

My model class is DeviceModel

Your model class should be QStandardItemModel. Are you subclassing the model?

P.S.

item.

as mentioned previously, you should avoid the allocation of QStandardItems on the stack as the model is supposed to own them

[mzimmers]

Yes:

class DeviceModel : public QStandardItemModel
{
private:
    ModelData deviceTable;
    QStandardItem item;
...

EDIT:

Ohhhhhh...okay.

[mrjj]

so it would be like

DeviceModel::DeviceModel()
{
    QString s1 = "aaa", s2 = "bbb", s3 = "ccc";
    QVariant qv;
     QStandardItem * item = new   QStandardItem (); // model will clean up
    qv = s1;
    item->setData(qv, DeviceRoles::macAddr);
    qv = s2;
    item->setData(qv, DeviceRoles::devName);
    qv = s3;
    item->setData(qv, DeviceRoles::latestTimestamp);
    appendRow(item); 
}

[VRonin]

You should have something like this:

#include <QApplication>
#include <QStandardItemModel>
#include <QTableView>
#include <QDateTime>
#include <QTimer>
#include <functional>
class ModelManager : public QObject{
    Q_OBJECT
    Q_DISABLE_COPY(ModelManager)
public:
    enum DeviceCols{
        dc_macAddr
        ,dc_devName
        ,dc_latestTimestamp
        
        ,dc_count
    };
    explicit ModelManager(QObject* parent = Q_NULLPTR)
        :QObject(parent)
        , m_model(new QStandardItemModel(this))
    {
        m_model->insertColumns(0,dc_count);
        m_model->setHeaderData(dc_macAddr,Qt::Horizontal,tr("Mac Address"));
        m_model->setHeaderData(dc_devName,Qt::Horizontal,tr("Name"));
        m_model->setHeaderData(dc_latestTimestamp,Qt::Horizontal,tr("Time Stamp"));
    }
    QAbstractItemModel* model() const {return m_model;}
public slots:
    void addDevice(const QString& macAdr, const QString& name, const QDateTime& timeStamp){
        const int newRow = m_model->rowCount();
        m_model->insertRow(newRow);
        m_model->setData(m_model->index(newRow,dc_macAddr),macAdr);
        m_model->setData(m_model->index(newRow,dc_devName),name);
        m_model->setData(m_model->index(newRow,dc_latestTimestamp),timeStamp);
    }
    void updateDevice(int row, const QString& macAdr, const QString& name, const QDateTime& timeStamp){
        if(row<0 || row>=m_model->rowCount())
            return;
        m_model->setData(m_model->index(row,dc_macAddr),macAdr);
        m_model->setData(m_model->index(row,dc_devName),name);
        m_model->setData(m_model->index(row,dc_latestTimestamp),timeStamp);
    }
private:
    QAbstractItemModel* m_model;
};


int main(int argc, char *argv[])
{
    QApplication application(argc, argv);
    ModelManager manager;
    manager.addDevice(QStringLiteral("Foo"),QStringLiteral("Bar"),QDateTime::currentDateTime());
    manager.addDevice(QStringLiteral("Foo1"),QStringLiteral("Bar1"),QDateTime::currentDateTime());
    manager.addDevice(QStringLiteral("Foo2"),QStringLiteral("Bar2"),QDateTime::currentDateTime());
    QTableView view;
    view.setModel(manager.model());
    view.show();
    // simulate adding a device and updating one
    QTimer::singleShot(1000,&manager,std::bind(&ModelManager::addDevice,&manager,QStringLiteral("AddMac"),QStringLiteral("AddName"),QDateTime::currentDateTime().addSecs(1)));
    QTimer::singleShot(2000,&manager,std::bind(&ModelManager::updateDevice,&manager,1,QStringLiteral("UpdateMac"),QStringLiteral("UpdateName"),QDateTime::currentDateTime().addSecs(2)));
    return application.exec();
}

Of course, instead of the QTimer the updates should come from your workers

[mzimmers]

Beautiful.

I made a minor change to the update:

void Device::update(DeviceDetails d)
{
    int rowCnt = m_model->rowCount();
    int row ;

    for(row = 0; row < rowCnt; ++row)
    {
        if(m_model->index(row, dc_macAddr).data().toString() == d.macAddr)
        {
            break;
        }
    }

    if (row == rowCnt) // didn't find the Mac address; add a new row.
    {
        add(d);
    }
    else
    {
        m_model->setData(m_model->index(row, dc_macAddr), d.macAddr);
        m_model->setData(m_model->index(row, dc_devName), d.devName);
        m_model->setData(m_model->index(row, dc_latestTimestamp), d.latestHB);
    }
}

Using the QStandardItemModel is indeed much, much simpler than subclassing. Thanks for all the help.