Adding an item to a QListView

[postb99]

Hello,

In Qt examples, there are examples that usually go beyond my simple test program. I have a QListView in main windo. I don't use designer or Qt quick.

Why do I loose the itemName value? My program crashes after I add a new item to my model and thanks to debugging I see that I indeed have 3 items in my vector but there is a blank string rather than expected value for last item (the one I created by clicking on the button).

Thank you for pointing my learning coding errors.

Here is some shortened source code, I attach the whole source code to this post.

MyModel.h:

class MyModel : public QAbstractTableModel
 {
     Q_OBJECT
 public:
     MyModel(QObject *parent = 0);
     int rowCount(const QModelIndex &parent = QModelIndex()) const ;
     int columnCount(const QModelIndex &parent = QModelIndex()) const;
     QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const;
 
     void addItem(TestItem item);
 private:
     std::vector<TestItem*> m_items;
 public slots:
     void onButtonClicked();
 };

class MyModel : public QAbstractTableModel
 {
     Q_OBJECT
 public:
     MyModel(QObject *parent = 0);
     int rowCount(const QModelIndex &parent = QModelIndex()) const ;
     int columnCount(const QModelIndex &parent = QModelIndex()) const;
     QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const;

     void addItem(TestItem item);
 private:
     std::vector<TestItem*> m_items;
 public slots:
     void onButtonClicked();
 };

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TestItem.h:

class TestItem {
 
public:
    TestItem();
    TestItem(QString itemName);
    QString getName() const;
    void setName(QString itemName);
 
 
private :
    QString m_itemName;
};

class TestItem {

public:
    TestItem();
    TestItem(QString itemName);
    QString getName() const;
    void setName(QString itemName);


private :
    QString m_itemName;
};

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MyModel.cpp:

QVariant MyModel::data(const QModelIndex &index, int role) const
{
    int row = index.row();
       int col = index.column();
       // generate a log message when this method gets called
       qDebug() << QString("row %1, col%2, role %3")
               .arg(row).arg(col).arg(role);
 
 
       if(role == Qt::DisplayRole){
           if (col == 0) return (*m_items[row]).getName();
 
           return QString("Row%1, Column%2")
                   .arg(row + 1)
                   .arg(col +1);
       }
 
       return QVariant();
}
 
void MyModel::addItem(TestItem item)
{
    int nbRows = m_items.size();
    beginInsertRows(QModelIndex(), nbRows, nbRows);
    m_items.push_back(&item);
    endInsertRows();
}
 
void MyModel::onButtonClicked(){
    TestItem newItem("new element");
    addItem(newItem);
}

QVariant MyModel::data(const QModelIndex &index, int role) const
{
    int row = index.row();
       int col = index.column();
       // generate a log message when this method gets called
       qDebug() << QString("row %1, col%2, role %3")
               .arg(row).arg(col).arg(role);


       if(role == Qt::DisplayRole){
           if (col == 0) return (*m_items[row]).getName();

           return QString("Row%1, Column%2")
                   .arg(row + 1)
                   .arg(col +1);
       }

       return QVariant();
}

void MyModel::addItem(TestItem item)
{
    int nbRows = m_items.size();
    beginInsertRows(QModelIndex(), nbRows, nbRows);
    m_items.push_back(&item);
    endInsertRows();
}

void MyModel::onButtonClicked(){
    TestItem newItem("new element");
    addItem(newItem);
}

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QtListViewDemoQt4.zip

[wysota]

You are pushing a pointer to a local object which gets destroyed when you leave addItem() thus your list items point to invalid data. With this particular structure I'd advise to use QList<TestItem> rather than QList<TestItem*>.

[postb99]

This solved, thank you for this quick answer :-)