QTableView shows nothing

dheerendra

Where is the piece of code ? Is it in main function or somewhere else ?
Could be because query object is stack object. Try allocating in Heap.

t0msk

Code is in function:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

Heap? Do you mean like pointer?

t0msk

@dheerendra said in QTableView shows nothing:

Where is the piece of code ? Is it in main function or somewhere else ?
Could be because query object is stack object. Try allocating in Heap.

Thanks problem solved :)

How to know, when allocate in Heap and when as stack object?

mrjj

@t0msk

void mainwindow::some func() {

MyClass C; // stack
MyClass *D = new MyClass; // heap

} // here C will be deleted. ( runs out of scope) BUT D lives until deleted by programmer.

So when using new, you are using heap.

SGaist

Hi,

To add to my fellow, you are also not checking whether the database is opened correctly.

t0msk

@SGaist said in QTableView shows nothing:

Hi,

To add to my fellow, you are also not checking whether the database is opened correctly.

I am checking

if(db.open()) {

but i didnt include it in post :) but thank you anyway :)

@mrjj said in QTableView shows nothing:

@t0msk

void mainwindow::some func() {

MyClass C; // stack
MyClass *D = new MyClass; // heap

} // here C will be deleted. ( runs out of scope) BUT D lives until deleted by programmer.

So when using new, you are using heap.

yes i know, but i dont know when use pointer and when stack

mrjj

@t0msk said in QTableView shows nothing:

i dont know when use pointer and when stack

Well use stack when possible.
If the variable is to be used outside a function/live longer than the function where its declared , consider using new or adding it as a member variable.

t0msk

@mrjj said in QTableView shows nothing:

@t0msk said in QTableView shows nothing:

i dont know when use pointer and when stack

Well use stack when possible.
If the variable is to be used outside a function/live longer than the function where its declared , consider using new or adding it as a member variable.

yea, so I have to use "new" always, because everything is function :D ,

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)

Is function too (my problem) :D

mrjj

@t0msk
Yes
You do
QSqlQueryModel query;
..
ui->tableView->setModel(&query);

Here you use & to take adress of it.

So as soon as function ends query is deleted and view is empty.

You could move
QSqlQueryModel query; to .h file.
as member in mainwindow

t0msk

@mrjj said in QTableView shows nothing:

@t0msk
Yes
You do
QSqlQueryModel query;
..
ui->tableView->setModel(&query);

Here you use & to take adress of it.

So as soon as function ends query is deleted and view is empty.

You could move
QSqlQueryModel query; to .h file.
as member in mainwindow

Ah, thank you for explanation :)