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Data not displaying on the QTreeView, QTableView,QListView classes



  • Hi,

    1. I'm subclassing QAbstractTableModel class, called class Addressbookmodel and I'm populating the model.

    2. On QWidget, I'm creating QVBoxLayout and setting it as the main layout for the view and adding QTreeView,QTableView,QListView objects to it.

    3. file path and accessing are working fine.
      But problem is,

    4. QTreeView, QTableview created on a stack is not getting displayed on the widget(at least it should show the layout of the widget, right?, why object created on the heap are shown because I have created QListView on heap memory, it is shown on the widget with empty data from the model

    5. why the model data is not showing?

    code: widget.cpp

    Widget::Widget(QWidget *parent)
    : QWidget(parent)
    {
    QFile file("path");
    if(!file.open(QIODevice::ReadOnly|QIODevice::Text))
    {
    qDebug()<<"can't access the file";
    }
    QString addresses=QString::fromUtf8(file.readAll());
    Addressbookmodel model(addresses);
    
    QListView *listView=new QListView();
    listView->setModel(&model);
    listView->setModelColumn(0);
    listView->show();
    
    QTreeView treeView;
    treeView.setModel(&model);
    treeView.show();
    
    QTableView tableView;
    tableView.setModel(&model);
    tableView.show();
    
    setMiniumSize(800,400);
    QVBoxLayout *Vlayout=new QVBoxLayout(this);
    Vlayout->addWidget(listView);
    Vlayout->addWidget(&treeView);
    Vlayout->addWidget(&tableView);
    }
    

    csv file:
    'Name', 'Address'
    'thippu', 'talacaverlayout'



  • @thippu said in Data not displaying on the QTreeView, QTableView,QListView classes:

    QTreeView, QTableview created on a stack is not getting displayed

    Because they go out of scope and get deleted before they can get displayed. The same is true for your model



  • @thippu

    Addressbookmodel model(addresses);
    QTreeView treeView;
    QTableView tableView;
    

    Exactly as @VRonin says: all three of these need to be allocated on the heap (new ...) for them to persist once the code you show in your Widget constructor has exited. Or, you might get away with making them members (without new) of your Widget class itself, if that lifetime is sufficient. (As per @VRonin below, just don't try that way, stick to new!)



  • @JonB said in Data not displaying on the QTreeView, QTableView,QListView classes:

    Or, you might get away with making them members

    If you do you must be careful that they must go out of scope before the parent tries to call delete on them. Usually it's not worth the effort and it's just better to allocate widgets on the heap



  • @VRonin
    That's why I said "might get away with". I know how fond you C++ people here are about using the stack instead of the heap if at all possible (whereas I am Python/PyQt and so just use the heap the whole time :) ), so I put that in in case someone complained, I did wonder about it. I'll just cross it through!



  • @JonB said in Data not displaying on the QTreeView, QTableView,QListView classes:

    . (As per @VRonin below, just don't try that way, stick to new!)

    Sure.



  • @JonB , @VRonin I want to learn model/view architecture, so I picked up the Book Qt 4 art of building to study and practice, went to 207 page for basic understanding and page 222 example I want to study and implement,

    1. They have told to store the .csv file format like this :
      ’’title (column 1)’’, ’’title (column 2)’’, ...,’’title (column n)’’
      ’’value’’, ’’value’’, ..., ’’value’’
      ’’value’’, ’’value’’, ..., ’’value’’
      ’’value’’, ’’value’’, ..., ’’value’’
      if I store like this and do qDebug() on theQList object, which has all the values of lines, it is giving output "" "" so, I did change the format and stored like this with values :
      csv file:
      'Name', 'Address'
      'thippu', 'talacaverlayout'
      after this change, qDebug() did show file data.
    2. output and Ui
      2)Not understanding why the data is not displaying on the Views.
      code AddressbookGui:
    //csv file read method.
    QStringList splitCSVLine(const QString& line)
    {
    bool inItem = false;
    QStringList items;
    QString item;
    for (int pos = 0; pos < line.length(); pos++)
    {
    QChar c=line.at(pos);
    if ( c == ’\’’) {
    if (inItem) {
    items.append(item);
    item = "";
    }
    inItem = !inItem;
    }
    else
    if (inItem) {
    item += c;
    }
    }
    return items;
    }
    
    //constructor
    AddressbookModel::AddressbookModel(const QString& addresses,
    QObject *parent): QAbstractTableModel(parent)
    {
    QStringList records = addresses.split(’\n’);
    QStringList line;
    foreach(QString record, records)
    addressBook.append(splitCSVLine(record));
    }
    
    
    int AddressbookModel::rowCount(const QModelIndex &parent ) const
    {
    Q_UNUSED(parent);
    return addressBook.count() - 2;
    }
    
    
    //rowCount method
    int AddressbookModel::columnCount(const QModelIndex &parent ) const
    {
    Q_UNUSED(parent);
    return addressBook.at(0).count();
    }
    
    //headerData method
    QVariant AddressbookModel::headerData(int section,Qt::Orientation orientation, int role) const
    {
    if (orientation == Qt::Horizontal) 
    {
    if (role == Qt::DisplayRole) 
    {
     return addressBook.at(0).at(section);
    }
    }
    return QAbstractTableModel::headerData(section, orientation, role);
    }
    
    
    //data method
    QVariant AddressbookModel::data(const QModelIndex &index,
    int role) const
    {
    if (!index.isValid()) return QVariant();
    QStringList addressRecord = addressBook.at(index.row()+1);
    if (role == Qt::DisplayRole || role == Qt::EditRole) {
    return addressRecord.at(index.column());
    }
    if (role == Qt::ToolTipRole) {
    QString tip, key, value;
    tip = "<table>";
    int maxLines = addressRecord.count();
    for (int i = 0; i < maxLines; i++) {
    key = headerData(i, Qt::Horizontal, Qt::DisplayRole)
    .toString();
    value = addressRecord.at(i);
    if (!value.isEmpty())
    tip += QString("<tr><td><b>%1</b>: %2</td></tr>")
    .arg(key, value);
    }
    tip += "</table>";
    return tip;
    }
    return QVariant();
    }
    
    
    
    


    1. pass your model through the Model Test
    2. make sure it survives and doesn't go out of scope as your views did


  • @VRonin Yeah, I did that no errors, bro.
    code what I did is: inside QWidget.

    new QAbstractItemModelTester(model,QAbstractItemModelTester::FailureReportingMode::Fatal);
    
    


  • @thippu
    As @VRonin asked, how do we know from the code you post what the scope/lifetime of your AddressbookModel instance is?



  • @JonB I did convert all the objects from stack memory to heap, I'm not getting what you need?



  • @JonB
    And also I did modelTest, There was no error.



  • @JonB changed all to the heap, I think they will stay till application die, right?
    code I have changed:

    Widget::Widget(QWidget *parent)
    : QWidget(parent)
    {
    QFile file("path");
    if(!file.open(QIODevice::ReadOnly|QIODevice::Text))
    {
    qDebug()<<"can't access the file";
    }
    QString *addresses=new QString(QString::fromUtf8(file.readAll()));
    Addressbookmodel *model=new Addressbookmodel(addresses,this);
    
    QListView *listView=new QListView();
    listView->setModel(model);
    listView->setModelColumn(0);
    listView->show();
    
    QTreeView *treeView=new QTreeView;
    treeView.setModel(model);
    treeView.show();
    
    QTableView *tableView=new QTableView;
    tableView.setModel(model);
    tableView.show();
    
    setMiniumSize(800,400);
    QVBoxLayout *Vlayout=new QVBoxLayout(this);
    Vlayout->addWidget(listView);
    Vlayout->addWidget(treeView);
    Vlayout->addWidget(tableView);
    }
    


  • @thippu

    Addressbookmodel *model=new Addressbookmodel(addresses,this);
    treeView.setModel(&model);
    tableView.setModel(&model);
    

    Now that model is a pointer, why the &s?



  • @JonB Sorry, typo mistake.



  • @JonB I did copy and paste from the early reply, So



  • I'm surprised you don't get into stack overflow.
    AddressbookModel::rowCount and AddressbookModel::columnCount form an infinitely deep tree.

    You should return 0; if the parent argument isValid()



  • @VRonin okay,
    In the Addressbookmodel.cpp
    I changed the code to :

    int Addressbookmodel::rowCount(const QModelIndex &parent) const
    {
       if(parent.isValid())
    {
      return 0;
    }
    return addressbook.count-2;
    }
    
    
    int Addressbookmodel::columnCount(const QModelIndex &parent)
    const
    {
      if(parent.isValid())
      {
       return 0;
      }
    return addressbook.at(0).count();
    }
    
    

    I don't know why it is not used in the book and why am not getting data on the widgets still?.



  • @VRonin Can share me an example that helps me to understand how to create QTreeView model and subclass it?, so from this I can able to create my own models successfully.



  • @thippu said in Data not displaying on the QTreeView, QTableView,QListView classes:

    Can share me an example that helps me to understand how to create QTreeView model and subclass it?

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



  • @VRonin , Thank you.


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