Thread: [Qt] Functions cannot access objects defined in the same class .. ! Possibly a bug ?
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ahmadka is offline ahmadka
2010-07-05 , 13:07
Posts: 341 | Thanked: 57 times | Joined on Nov 2009
#1
This first issue has been solved (my silly mistake!):

Hey guys .. Well ever since I've started programming in Qt, I've been having problems regarding scope visibility of objects I've defined .. Till now I've managed to find ways to get around these things but now its getting annoying ..

For example, I have this class defined called Canvas:

Code:
class Canvas : public QWidget//, public MainWindow
{
    Q_OBJECT
public:
    void refreshFoldersList(QString inputPath);
    void browseFolders();

private:
    QListWidget *foldersList;

};

#endif // CANVAS_H

Now even though foldersList is private, refreshFoldersList() should be able to 'see' it, right ? But in my case it can't .. ! I first initialize foldersList in the browseFolders() function and then from within browseFolders(), I call refreshFoldersList() ... Any code inside refreshFoldersList() dealing with foldersList immediately throws a segmentation fault ... I've checked the pointer values for foldersList when the scope is in browseFolders() and refreshFoldersList() .. the values don't match .. its like either I'm trying to access something I'm not supposed to, or that I'm trying to access an object which has not been initialized yet ..

Any clues on this ?

Second problem is still an ongoing issue:

A related issue ... I have another class MainWindow (inherited from QMainWindow) .. In this class I have an instance of the class Canvas .. this instance is named canvas .. I initialize canvas in MainWindow's constructor, and set canvas's parent to the MainWindow instance initializing it .. based on this, I used the following code to access a MainWindow function from within the Canvas class:

Code:
((MainWindow*)parent())->someFunctionDefinedInMainWindow();
Before, the above code used to work .. but then like 2-3 days ago it stopped working all of a sudden .. Now it got me to inside the MainWindow function I was calling (namely someFunctionDefinedInMainWindow() ), but from there if I tried to access any variable defined in MainWindow, I got a Segmentation Fault, again with pointer values not matching .. The way I solved this is by defining a variable as:

Code:
void * papa;
.. inside Canvas, and then when I initialized canvas, I set:

Code:
canvas->papa = this; //this being the MainWindow instance initializing canvas
Now I accessed MainWindow's functions like this:

Code:
((MainWindow*)papa)->someFunctionDefinedInMainWindow();
.. which works!

But again, I would like to know the nature of these problems .. Am I doing something wrong or what ?
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Last edited by ahmadka; 2010-07-05 at 14:59.