QTableView shows nothing

[t0msk]

Hello, this is my code:

    db.open();

    QSqlQueryModel query;
    query.setQuery("SELECT * FROM pve.010_store");

    ui->tableView->setModel(&query);

But, when I launch program it shows nothing..

Screenshot:

Where is a problem? :/

[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 :)