qobject_cast "good coding practice"

[janus]

Hi,

i wonder what is a better practice of passing pointers to childwidgets (if their is anything like a common good practice ) of this two possibilities: Passing the Baseclass or MyClass?

I have a MainWindow and need to pass a pointer to subclass of QSqlTableModel to a childwidget:

mainwindow.cpp

MyQSqlTableModel *tm = new  MyQSqlTableModel;
ChildWidget *cw = new ChildWidget( this );
cw->setTableModel( tm );

MyQSqlTableModel *tm = new  MyQSqlTableModel;
ChildWidget *cw = new ChildWidget( this );
cw->setTableModel( tm );

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1. childwidget.cpp

void ChildWidget::setTableModel( QAbstractItemModel *model )
{
     m_model = qobject_cast<MyQSqlTableModel *>(model);
     m_model->doSomething();

void ChildWidget::setTableModel( QAbstractItemModel *model )
{
     m_model = qobject_cast<MyQSqlTableModel *>(model);
     m_model->doSomething();

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2. childwidget.cpp

void ChildWidget::setTableModel( MyQSqlTableModel *model )
{
     m_model = model;
     m_model->doSomething();

void ChildWidget::setTableModel( MyQSqlTableModel *model )
{
     m_model = model;
     m_model->doSomething();

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I have seen both and wonder what the difference is and what the better approach might be.

[caduel]

I prefer the 2nd. It states what really must be passed (whereas the 1st lets the compiler tolerate errors that will manifest themselves at runtime).
(Exceptions are when you inherit a class and have no choice in the signature.)