Qt and Templates

[franz]

Try something like

template<typename T>
class TableModel : public QAbstractTableModel
{
    Q_OBJECT
 
public:
    explicit TableModel(QObject *parent = 0);
    ....
 
private:
    typename QList<T *> records;
    ....
};

template<typename T>
class TableModel : public QAbstractTableModel
{
    Q_OBJECT

public:
    explicit TableModel(QObject *parent = 0);
    ....

private:
    typename QList<T *> records;
    ....
};

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It's dry coded and un-tested, but I'd expect it to behave like you want:

TableModel<Street> *model = new TableModel<Street>();

TableModel<Street> *model = new TableModel<Street>();

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Note that this might mean a lot of the code needs to be templated, which means you're going to have to put all that implementation in a header file. Be sure to document the requirements on T. Also, given the nature of the example classes you give, you can consider not using pointers in your list. This will probably make management of the records much simpler. If that's possible, use

typename QList<T> records;

typename QList<T> records;

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instead.

[jsmax]

Try something like

template<typename T>
class TableModel : public QAbstractTableModel
{
    Q_OBJECT
 
public:
    explicit TableModel(QObject *parent = 0);
    ....
 
private:
    typename QList<T *> records;
    ....
};

template<typename T>
class TableModel : public QAbstractTableModel
{
    Q_OBJECT

public:
    explicit TableModel(QObject *parent = 0);
    ....

private:
    typename QList<T *> records;
    ....
};

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I get errors on line 11 in your code:

error: expected nested-name-specifier
error: invalid declarator before 'records'

This is my class (i get the same errors in my class):

template<typename TPL>
class JSONTableModel : public QAbstractTableModel
{
    Q_OBJECT
 
public:
    explicit JSONTableModel(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;
    bool setData ( const QModelIndex & index, const QVariant & value, int role = Qt::EditRole );
    QVariant headerData ( int section, Qt::Orientation orientation, int role = Qt::DisplayRole ) const;
    Qt::ItemFlags flags ( const QModelIndex & index ) const;
 
    int getTotalRecordsCount();
    int getFetchedRecordsCount();
    QString getParam(QString);
    QString getHeaderKey(int);
    void setParam(QString, QString);
 
private:
    typename QList<TPL *> records;
    QMap<QString, QString> headers;
    QMap<QString, QString> params;
    QNetworkAccessManager *manager;
    QModelIndex updatingIndex;
    QString url;
    int totalRecords;
 
signals:
    void dataLoaded();
    void requestStarted();
 
public slots:
    void loadRecords();
    void replyFinished(QNetworkReply*);
};

template<typename TPL>
class JSONTableModel : public QAbstractTableModel
{
    Q_OBJECT

public:
    explicit JSONTableModel(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;
    bool setData ( const QModelIndex & index, const QVariant & value, int role = Qt::EditRole );
    QVariant headerData ( int section, Qt::Orientation orientation, int role = Qt::DisplayRole ) const;
    Qt::ItemFlags flags ( const QModelIndex & index ) const;

    int getTotalRecordsCount();
    int getFetchedRecordsCount();
    QString getParam(QString);
    QString getHeaderKey(int);
    void setParam(QString, QString);

private:
    typename QList<TPL *> records;
    QMap<QString, QString> headers;
    QMap<QString, QString> params;
    QNetworkAccessManager *manager;
    QModelIndex updatingIndex;
    QString url;
    int totalRecords;

signals:
    void dataLoaded();
    void requestStarted();

public slots:
    void loadRecords();
    void replyFinished(QNetworkReply*);
};

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[stampede]

"typename" is not needed in this case, its needed when the template parameter has a nested type and you want to use it:

template<class T>
class Test{
public:
    Test(){
        // T::NestedClass t; // this wont compile
         typename T::NestedClass t; // this is ok
    }
};

template<class T>
class Test{
public:
    Test(){
        // T::NestedClass t; // this wont compile
         typename T::NestedClass t; // this is ok
    }
};

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[jsmax]

QObject classes does not support templates

During compilation i get this:

Error: Template classes not supported by Q_OBJECT

[wysota]

They do, only that you can't use Q_OBJECT macro with a template class. You need to subclass twice -- first introduce Q_OBJECT, define all the signals and slots you want and then subclass again and introduce the template.