[SOLVED]which widget would be the best to display the following data?



  • I am implementing an application that communicates to an end device via usb/serial every second. I need a control that will list all the register name and the current value of the registers for the device. I was thinking about using a QTableview to do this but it looks like it may take a long time to do any updates to the table for I don´t see anyway to directly assign a register to a row. NOTE: my register data is stored in a struct array. Every second, I poll the device registers, store the data to my array, and emit a signal if the value I have stored for a particular register does not that of the value I just polled. Thanks ahead for your time and effort...



  • Itemview widgets are very good candidates to solve your problem.
    Choose among QTableView, QListView or QTreeView depending on the structure of your data.
    1 record per second is not a problem at all. If your experiments showed a behaviour which was too sluggish I suspect that you did not emit the dataChanged signal when a new record arrived.

    If you do not want to mess around with model view programming your usecase can also be solved with QTableWidget or QTreeWidget.



  • Item views would definitly fit best. The update frequency should also not be a problem, we have some similar szenario here. We use a table views for thos data displays. For some also trees.

    What we do is we have some background thread collecting the data and doing comparsion and only send data changes to the model which then updates the view. The tests for did for performance showed us that trees with many items (>10000) whould get a bit slowely....



  • Hi Gerolf,

    I am assuming you are using the model/view programming approach. Do you happen to have code snippets of your implementation that I can view? Since the first reply to this post, I´ve looked at the model/view tutorial. I kind of understand the concept, however, the auto-data population and the capturing of the user editing value is what I am still a little puzzled on. Thanks for your time and support...



  • It sounds like that you don't have to bother with users editing the data, as your data is for display purposes and is updated by your backend. That makes implementing the model simpler.
    What is important to remember, is that you try to be as specific as possible in signalling what data has changed. Only then, the view can optimize properly what part of the view needs to be withdrawn.



  • Hi phamtv,

    sorry, no code snippets here. It's closed source. But It's not difficult. I suggest to first implement the model displaying the data without updates from a background thread. Think of the data structures to display and display them (in a tree view, table view, however). When this is working, implement the collector thread and create the data tree there.

    What is then missing is just: compare old tree with new tree, build diff data and send it via signal/slot to the model.



  • My tip: try to stick to a simple model at first, a list or a table. Don't start your first model implementation with a tree model. They are just plain hard. For a table model, you can start with subclassing QAbstractTableModel, which simplifies the interface for QAbstractItemModel for the table case.



  • phamtv,
    Qt 4.7.1 comes with a neat tutorial which shows also how to deal with changing models.
    http://doc.qt.nokia.com/4.7/modelview.html

    interesting for you: 2.3, a clock inside a table cell.



  • dialingo/Andre/Gerolf,

    I have the following code implementation, however, when I run the application, the tableview controls is shown but does not populate with the rows and columns data... Any idea what is going on? NOTE: I simplified it into 3 files...

    @
    // File: cls_device.h
    #ifndef CLS_DEVICE_H
    #define CLS_DEVICE_H

    #include <QtGui>
    #include <QObject>
    #include <QThread>
    #include <QMap>
    #include <QtDebug>

    struct RegData
    {
    QString Desc;
    int Addr;
    double Value;
    };

    class RegisterModel : public QAbstractTableModel
    {
    Q_OBJECT
    public:
    RegisterModel(){}

    void setCurrencyMap(const QMap<QString, double> &map)
    {
        registerMap = map;
        reset();
    }
    
    int rowCount(const QModelIndex & /* parent */) const
    {
        qDebug() << registerMap.count();
        return registerMap.count();
    }
    
    int columnCount(const QModelIndex & /* parent */) const
    {
        return 2; //registerMap.count();
    }
    Qt::ItemFlags flags(const QModelIndex & index) const
    {
        if (index.column() == 0)
            return Qt::ItemIsSelectable | Qt::ItemIsEnabled ;
        else
            return Qt::ItemIsSelectable |  Qt::ItemIsEditable | Qt::ItemIsEnabled ;
    }
    bool setData(const QModelIndex & index, const QVariant & value, int role)
    {
        if (index.isValid() && role == Qt::EditRole)
        {
            ValueAt(index.row()) = value.toString();
        }
        return true;
     }
    QVariant data(const QModelIndex &index, int role) const
    {
        // NOTE: int role == Qt.ItemDataRole
    
        if (!index.isValid())
            return QVariant();
    
        switch(role)
        {
        case Qt::TextAlignmentRole:
            if (index.column() == 0)
                return int(Qt::AlignLeft | Qt::AlignVCenter);
            else if (index.column() == 1)
                return int(Qt::AlignHCenter | Qt::AlignVCenter);
            else
                return QVariant();
            break;
        case Qt::DisplayRole:
            if (index.column() == 0)
                return DescAt(index.row());
            else if (index.column() == 1)
                return ValueAt(index.row());
            else
                return QVariant();
            break;
        }
        return QVariant();
    }
    
    QVariant headerData(int section, Qt::Orientation orientation, int role) const
    {
        if (role != Qt::DisplayRole)
            return QVariant();
    
        if (orientation == Qt::Horizontal)
            return (section == 0) ? "Register" : "Value";
        else
            DescAt(section);
    }
    

    private:
    QString DescAt(int offset) const
    {
    return (registerMap.begin() + offset).key();
    }

    QString ValueAt(int offset) const
    {
        return QString("%1").arg((registerMap.begin() + offset).value());
    }
    
    QMap<QString, double> registerMap;
    

    };

    class cls_Device : public QThread
    {
    Q_OBJECT

    public:
    RegData* data[10];

    cls_Device()
    {
        for (int i = 0; i < 10; i++)
        {
            // example
            if (i == 5)
            {
                data[i] = NULL;
                continue;
            }
            data[i] = new RegData();
            data[i]->Desc = QString("Register %1").arg(i);
    
            qDebug() << data[i]->Desc;
    
            data[i]->Addr = i;
            data[i]->Value = 1;
        }
    }
    ~cls_Device(){}   // destructor
    
    void run()
    {
        Read();
    }
    
    void Read()
    {
        for (int i = 0; i < 10; i++)
        {
    
        }
    }
    void Write()
    {
    }
    

    signals:

    public slots:

    };

    #endif // CLS_DEVICE_H

    // file: mainwindow.h
    #ifndef MAINWINDOW_H
    #define MAINWINDOW_H

    #include <QMainWindow>
    #include <QTableView>
    #include <QLayout>
    #include <cls_device.h>
    #include <currencymodel.h>

    //namespace Ui {
    // class MainWindow;
    //}

    class MainWindow : public QMainWindow
    {
    Q_OBJECT

    public:
    QMap<QString, double> registerMap;
    cls_Device* device;

    explicit MainWindow(QWidget *parent = 0)
    {
        device = new cls_Device();
        for (int i = 0; i < 10; i++)
        {
            if (device->data[i] != NULL)
                registerMap.insert(device->data[i]->Desc, device->data[i]->Value);
        }
    
        RegisterModel registerModel;
        registerModel.setCurrencyMap(registerMap);
    
        QTableView* tableView = new QTableView();
        tableView->setModel(&registerModel);
        tableView->setAlternatingRowColors(true);
        tableView->verticalHeader()->hide();
        tableView->horizontalHeader()->setStretchLastSection(true);
        tableView->resizeColumnsToContents();
        tableView->setSelectionBehavior(QAbstractItemView::SelectRows);
        setCentralWidget(tableView);
    
        QTimer* timer = new QTimer(this);
        timer->setInterval(1000);
        connect(timer, SIGNAL(timeout()) , this, SLOT(timerHit()));
        timer->start();
    }
    ~MainWindow()
    {
        disconnect();
    
        if (device != NULL)
            delete device;
    }
    

    public slots:
    void timerHit()
    {
    }

    };
    #endif // MAINWINDOW_H

    // File: main.cpp
    #include <QObject>
    #include <QtGui>
    #include <mainwindow.h>

    int main(int argc, char *argv[])
    {
    QApplication app(argc, argv);

    MainWindow window;
    window.showMaximized();
    return app.exec();
    

    }
    @



  • You should create your model on the heap, not on the stack ( line 193 ). Now, your model is destroyed again before the data is actually shown.



  • Hi,

    the problem is pretty easy:

    you create the register model on the stack
    set it to the view and then, when the c'tor goes out of scope, the model is deleted.

    create the reister model on the heap as follows:

    @

    explicit MainWindow(QWidget *parent = 0)
    {
        device = new cls_Device();
        for (int i = 0; i < 10; i++)
        {
            if (device->data[i] != NULL)
                registerMap.insert(device->data[i]->Desc, device->data[i]->Value);
        }
    
        RegisterModel* registerModel = new RegisterModel(this);
        registerModel->setCurrencyMap(registerMap);
    
        QTableView* tableView = new QTableView();
        tableView->setModel(registerModel);
        tableView->setAlternatingRowColors(true);
        tableView->verticalHeader()->hide();
        tableView->horizontalHeader()->setStretchLastSection(true);
        tableView->resizeColumnsToContents();
        tableView->setSelectionBehavior(QAbstractItemView::SelectRows);
        setCentralWidget(tableView);
    
        QTimer* timer = new QTimer(this);
        timer->setInterval(1000);
        connect(timer, SIGNAL(timeout()) , this, SLOT(timerHit()));
        timer->start();
    }
    

    @

    aditionally, the creator of RegisterModel should look like this:

    @
    RegisterModel(QObject* pParent) :
    QAbstractTableModel(pParent)
    {
    }

    @



  • thanks Gerolf for the quick response!!!



  • -Actually, the code Gerolf presents causes a memory leak. Don't forget to give the model a parent in on line 13 of that piece of code. Candidates for parents are the form, or the view itself.-

    I misread the code, there is no leak.



  • Andre, let me correct you.
    The memory leak does not exist, as setCentralWidget reparents the widget (look at the docs) and takes the ownership.

    But I also think, it looks better to give the QTableView a parent on construction....



  • I am sorry, you are right. I misread the code, and thought you did not give the model a parent. But you do. I stand corrected.



  • Thanks guys for your support. I have a follow up question to my model/view implementation. I added some code to spawn another thread to generate some random number, however, I don´t know how to update the table view when I receive the signal to update the table view. Can you guys give me some input? Thanks!

    @
    // file: cls_device.h
    #ifndef CLS_DEVICE_H
    #define CLS_DEVICE_H

    #include <QtGui>
    #include <QObject>
    #include <QThread>
    #include <QMap>
    #include <QtDebug>

    struct RegData
    {
    QString Desc;
    int Addr;
    double Value;
    };

    class RegisterModel : public QAbstractTableModel
    {
    Q_OBJECT
    public:
    RegisterModel(QObject* pParent) :
    QAbstractTableModel(pParent){}

    void setCurrencyMap(const QMap<QString, double> &map)
    {
        registerMap = map;
        reset();
    }
    
    int rowCount(const QModelIndex & /* parent */) const
    {
        return registerMap.count();
    }
    
    int columnCount(const QModelIndex & /* parent */) const
    {
        return 2; //registerMap.count();
    }
    Qt::ItemFlags flags(const QModelIndex & index) const
    {
        if (index.column() == 0)
            return Qt::ItemIsSelectable | Qt::ItemIsEnabled ;
        else
            return Qt::ItemIsSelectable |  Qt::ItemIsEditable | Qt::ItemIsEnabled ;
    }
    bool setData(const QModelIndex & index, const QVariant & value, int role)
    {
        if (index.isValid() && role == Qt::EditRole)
        {
            ValueAt(index.row()) = value.toString();
        }
        return true;
     }
    QVariant data(const QModelIndex &index, int role) const
    {
        // NOTE: int role == Qt.ItemDataRole
    
        if (!index.isValid())
            return QVariant();
    
        switch(role)
        {
        case Qt::TextAlignmentRole:
            if (index.column() == 0)
                return int(Qt::AlignLeft | Qt::AlignVCenter);
            else if (index.column() == 1)
                return int(Qt::AlignHCenter | Qt::AlignVCenter);
            else
                return QVariant();
            break;
        case Qt::DisplayRole:
            if (index.column() == 0)
                return DescAt(index.row());
            else if (index.column() == 1)
                return ValueAt(index.row());
            else
                return QVariant();
            break;
        }
        return QVariant();
    }
    
    QVariant headerData(int section, Qt::Orientation orientation, int role) const
    {
        if (role != Qt::DisplayRole)
            return QVariant();
    
        if (orientation == Qt::Horizontal)
            return (section == 0) ? "Register" : "Value";
        else
            DescAt(section);
    }
    

    private:
    QString DescAt(int offset) const
    {
    return (registerMap.begin() + offset).key();
    }

    QString ValueAt(int offset) const
    {
        return QString("%1").arg((registerMap.begin() + offset).value());
    }
    
    QMap<QString, double> registerMap;
    

    };

    class cls_Device : public QThread
    {
    Q_OBJECT

    public:
    RegData* data[10];

    cls_Device()
    {
        for (int i = 0; i < 10; i++)
        {
            // example
            if (i == 5)
            {
                data[i] = NULL;
                continue;
            }
            data[i] = new RegData();
            data[i]->Desc = QString("Register %1").arg(i);
            data[i]->Addr = i;
            data[i]->Value = 1;
        }
    }
    ~cls_Device(){}   // destructor
    
    void run()
    {
        Read();
    }
    
    void Read()
    {
        int min = 0;
        int max = 255;
    
        for (int i = 0; i < 10; i++)
        {
            double val = int( random() / (RAND_MAX + 1.0) * (max + 1 - min) + min );
            if ((data[i] != NULL) && (data[i]->Value != val))
            {
                data[i]->Value = val;
                emit RegisterValueChanged(this, data[i]);
            }
        }
    }
    void Write()
    {
    }
    

    signals:
    void RegisterValueChanged(QObject* obj, RegData* e);
    public slots:

    };

    #endif // CLS_DEVICE_H

    // file: mainwindow.h
    #ifndef MAINWINDOW_H
    #define MAINWINDOW_H

    #include <QMainWindow>
    #include <QTableView>
    #include <QLayout>
    #include <cls_device.h>
    #include <currencymodel.h>

    class MainWindow : public QMainWindow
    {
    Q_OBJECT

    public:
    QMap<QString, double> registerMap;
    cls_Device* device;

    explicit MainWindow(QWidget *parent = 0)
    {
        device = new cls_Device();
        connect(device, SIGNAL(RegisterValueChanged(QObject*,RegData*)),
                this, SLOT(RegisterValueChanged(QObject*,RegData*)), Qt::QueuedConnection);
    
        for (int i = 0; i < 10; i++)
        {
            if (device->data[i] != NULL)
                registerMap.insert(device->data[i]->Desc, device->data[i]->Value);
        }
    
        RegisterModel* registerModel = new RegisterModel(this);
        registerModel->setCurrencyMap(registerMap);
    
        QTableView* tableView = new QTableView(this);
        tableView->setModel(registerModel);
        tableView->setAlternatingRowColors(true);
        tableView->verticalHeader()->hide();
        tableView->horizontalHeader()->setStretchLastSection(true);
        tableView->resizeColumnsToContents();
        tableView->setSelectionBehavior(QAbstractItemView::SelectRows);
        setCentralWidget(tableView);
    
        QTimer* timer = new QTimer(this);
        timer->setInterval(1000);
        connect(timer, SIGNAL(timeout()) , this, SLOT(timerHit()));
        timer->start();
    }
    ~MainWindow()
    {
        disconnect();
    
        if (device != NULL)
            delete device;
    }
    

    public slots:
    void timerHit()
    {
    if (!device->isRunning())
    device->start();
    }

    private slots:
    void RegisterValueChanged(QObject* obj, RegData* e)
    {
    qDebug() << QString("How do I update the table view for Register address %1 with value %2").arg(e->Addr).arg(e->Value);
    }
    };

    #endif // MAINWINDOW_H

    // file main.cpp
    //use the previous code snippet

    @



  • You should start reading the "docs":http://doc.qt.nokia.com/4.7/modelview.html :-)
    When you want to change a value, you have to emit a signal dataChange() and change the value before.
    If you want to add/remnove rows/columns, there are also signals, which are emitted by special functions

    [begin|end][insert|remove][Columns|rows]



  • Hi Gerolf, Thanks!, :-) I have been reading the docs but just can´t seem to connect things together. As you can see in my implementation, I have an inherited QThread class that initializes my structure pointer array. If you have noticed, I intentionally place a null pointer to register 5 because I do not have a continguous set of register in my real world scenario. QMap basically is a subset of my structure pointer array without the null pointer. I can populate the table view with RegisterModel using QMap. However, as you can see, when my thread executes, it changes the structure array value. Do I have to loop through the QMap items, compare the description strings, and then update TableView by emitting a signal dataChange()? This seem time consuming if I have loop through the QMaps items for every registers that changes.... Please advise...


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