I got 2 classes:
- MainWindow (Was the default class)
- ExtraClass (That i created myself)
Inside the class MainWindow i've made a public function called "logger". This function looks like this:
// Takes in a QString and appends it to a QTextEdit.
void MainWindow::logger(QString Log_MSG)
{
ui->Logg->append(Log_MSG);
}
This logger functions works out as expected inside its own Class MainWindow but when i try to pass in a MSG into logger from the class ExtraClass, it suddenly doesn't work.
My approach to accessing logger from MainWindow to ExtraClass:
MainWindow Con;
Con.logger("The Message the will get appended to ui->logg");
So the question, what have i missed? I don't get any errors and the text "Log_MSG" that should be appended to the QTextEdit Log don't execute.
Sorry for the style, i just don't understand how to get it to look good.
EDIT:
I've already tried to access other functions from "MainWindow class"
and that works but when i try to pass a string this particuallry function "logger"
from another class nothing happens.
For an instance:
MainWindow MainWindow;
int ANumber = MainWindow.GiveMeAValue(); // This works
But when i'm doing this:
MainWindow MainWindow;
MainWindow.logger("Log MSG"); // This dosen't work
My guess is that the problem lies in the appendment of
a QString passed in into the main class that was automatically created by Qt (have stuff like ui->abc) from another class. But in my current
level of understandment of Qt i don't really know where to
troubleshoot beocuse i don't even get an error.
Your code to access the logger is wrong (it shouldn't even compile).
First, everytime you call the function where this code resides, you create a new local MainWindow object (Con). And then you try to call the method on the class and not on an object. If it is a static method (which I doubt, due to the use of ui), you would have to write MainWindow::logger(). If it is not a static method, then you need to call it on a specific MainWindow instance. But instead of creating a local MainWindow everytime, you should provide the correct application's MainWindow instance to your ExtraClass object.
If all this sounds alien to you, you should first look a bit deeper into fundamental C++ programming before delving into Qt.
Related
I know this is very clunky and I'm probably doing a lot of wrong things but so far everything I saw on the net gives back the same errors: invalid use of non-static data member ui.
So in the MainWindow, I have a comboBox named hometeam, and I want to display the currentText on a Qlabel named label which is on another Form Class called Dialog
I figured they're both private members so I added friend class MainWindow and friend class dialog in the respective headers (I know this is pretty wrong but it's the last thing I tried), I included the "ui_mainwindow" and "ui_dialog" in the .cpp files, and here's the bit of code I'm trying:
ui->label->setText(MainWindow::ui->hometeam->currentTex());
Keep in mind that I don't want a QDialog, the second window will do a lot more than a display, I just want to access the objects from a different window. Slots and signals give the same error.
Thanks !
I think the proper way to do that, is to add a function to your MainWindow class:
QString hometeamText() const
{
return ui->hometeam->currentTex();
}
This way you can access the information you need without violating encapsulation rules, but you need an instance of MainWindow to do it, and sure must keep a pointer to it in your Dialog class:
class Dialog
{
private:
MainWindow * mainwindow;
public:
void setMainWindow(MainWindow * w) { mainWindow = w; }
then somewhere (e.g. in main) you can do something like:
MainWindow mainwindow;
Dialog dialog;
dialog.setMainWindow(&mainWindow);
and from inside your Dialog class, wherever you need it:
ui->label->setText(window->hometeamText());
I'm sorry if this question is duplicate but i am really struggling with finding any answer.
Please take in mind that i am novice in c++ programmming.
My problem is this. I have an GUI made in QtCreator. There are two listeners binding keyReleaseEvent, one on main class (SuperFalcon) , one on QTextEdit ( which is separate and modified class ). I have QFrame which i would like to toggle hide/show on "Ctrl + f" key event. Since that QFrame (object name is findWidget) widget belongs to SuperFalcon->ui, there's no problem, everything works fine, problem starts when i try to make "Ctrl + f" in QTextEdit because it's separate event listener. Basically i tried this.
main class name is "SuperFalcon" so:
in superfalcon.h i've made an public static pointer like this:
public:
static QFrame *fWidget;
then in superfalcon.cpp, i firstly execute
ui->findWidget->hide(); and then
fWidget = ui->findWidget; hoping to get pointer on widget.
Next in my QTextEdit class in keyReleaseEvent function i've tried to get that pointer like SuperFalcon::fWidget->show() but i get undefined reference on it.
So , to make things simpler, i don't know how , if possible, to get reference of QFrame widget which is part of one class (SuperFalcon), from another class (QTextEdit class) in order to execute some commands on QFrame.
If it's not clear enough i can provide some code.
You must have a definition of any static member variable.
This definition has to be in a source file because of the one definition rule.
Simply add the line:
QFrame* SuperFalcon::fWidget;
to "superfalcon.cpp".
You have to initialize your static variable, in superfalcon.cpp:
QFrame* SuperFalcon::fWigdet = nullptr;
I'm wondering how to access parent class in my Qt application.
Lets say my project has following structure:
mainWindow: MainWindow
tabWidget: QTabWidget
tab1: MySubClass1
tab2: MySubClass2
tabWidget: QTabWidget
xtab1: MySubSubClass1
xtab2: MySubSubClass2
It is a little simplified.
What I want to do is to access mainWindows object from one of xtab2 slot functions.
(1) What would be the best method ?
I tried to pass the pointer to mainWindow along the tree but I get runtime errors.
(2) Should I include mainwindow.h in xtab.h file or should I do it in xtab.cpp file ?
Thanks for help :)
If you really need the mainwindow, passing the MainWindow pointer is the best way to do it. A static method has the drawback that it will stop working with more than one mainwindow.
I would suggest to avoid accessing the mainwindow from the contained widgets though and use signals instead. E.g.:
class MainWindow {
public:
explicit MainWindow( QWidget* parent=0 ) {
tab = new TabWidget;
...
MySubSubClass1* ssw1 = new MySubSubClass;
connect( ssw1, SIGNAL(textChanged(QString)), this, SLOT(page1TextChanged(QString));
tab->addWidget( ssw1 );
}
private Q_SLOTS:
void page1TextChanged( const QString& ) {
//do something...
}
};
MySubSubClass1 then emits textChanged(), addresseeChanged() (e.g. in Addressbook), or whatever level of abstraction or detail makes sense on the higher level. That way MySubSubClass is generic and doesn't have to know about MainWindow at all. It can be reused in any other context. If MySubSubClass itself contains other widgets, it can again connect to their signals.
You could create a static method and object inside MainWindow that would return mainwindow object.
Something like this:
private:
static MainWindow* _windowInstance
public:
static MainWindow* windowInstance()
{
return _windowInstance;
}
This seems to be the simples solution in most cases. Now you just have to include mainwindow.h whenever you need to access this object.
And don't forget to initialize _windowInstance in the contructor, like this;
_windowInstance = this;
By parent class, I assume you mean parent widget?
If you want to find the top level widget, QWidget::window() will point you to it. Use dynamic_cast or qobject_cast to turn it into your MainWindow object.
If you want to go up some arbitrary level, use paerntWidget().
There are a variety of different solutions to this problem, the one you chose as the answer is in terms of object orientation and encapsulation one of the worse ones. Some thoughts
Encapsulation: if you find yourself having to provide access accross a large distance in relation (down a long chain of containers or subclasses) you might want to look at the functionality that you are trying to distribute. I might be that it should be encapsulated in a class by itself that can passed around easier than where it is currently located (the main window in your case).
Abstraction: Unless it is actually functionality of QMainWindow that you need to access don't pass a pointer to your MainWindow class, create an interface for the functionality that you need, have your MainWindow implement that interface and pass around and object of the interface type instead of your MainWindow type.
Signals and Slots: As Frank noted, implement the appropriate functionality using Qt's signalling mechanism, this makes the connection between the caller and callee into a dynamic one, again separating it from the actual MainWindow class
QApplication: If you absolutely have to have global information restrict the entry point, you already have one singleton the QApplication object, make it the maintainer of all the other objects that need to be globally accessible, derive your own QApplication class and maintain global references in there. Your QApplication class can then create or destroy the needed global objects.
With more information about what you need to do with the MainWindow instance or what needs to be communicated you will also get better answers
QWidget* parent = this ;
while (parent -> parentWidget()) parent = parent -> parentWidget() ;
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:
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 ?
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:
((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:
void * papa;
.. inside Canvas, and then when I initialized canvas, I set:
canvas->papa = this; //this being the MainWindow instance initializing canvas
Now I accessed MainWindow's functions like this:
((MainWindow*)papa)->someFunctionDefinedInMainWindow();
.. which works!
But again, I would like to know the nature of these problems .. Am I doing something wrong or what ?
The bug is here (code from your comment to liaK):
QListWidget *foldersList = new QListWidget();
You are creating a local variable instead of initializing the class member. Change the code to:
foldersList = new QListWidget();
And probably there is no need for foldersList to be a pointer at all, so your class declaration could be:
private:
QListWidget foldersList;
throws a segmentation fault
Probably some error in your initialization.. How you are initializing it?? Showing the code will be helpful.
And you are using --> instead of ->
Check out this link
Sure it is not a bug with Qt.
or that I'm trying to access an object
which has not been initialized yet
Perhaps you are trying to access an object that hasn't been initialised yet? How and where do you initialise folderList?
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
If there was any problem with members visibility, your code wouldn't even compile. Your segfault must be related to something else.
I'm afraid you'll have to show more code for us to be able to help you efficiently.
Moreover, you're using C casts while Qt requires you to write C++. That can only make things worse.
So instead of:
((MainWindow*)parent())-->someFunctionDefinedInMainWindow();
You should use either dynamic_cast<> or static_cast<>, depending on what you want to achieve.
My friend and I have each created parts of a GUI using Qt 4. They both work independently and I am trying to integrate his form with the my main window. As of now this is the code I am using to try and load his form:
//connect buttons and such
connect(exitbtn, SIGNAL(triggered()),this,SLOT(terminated()));
connect(add, SIGNAL(triggered()),this,SLOT(add_rec()));
void MainWindowImpl::add_rec()
{
//form quits as soon as it loads...?
DialogImpl dia;//name of his form
dia.show();
}
I have included his header file. The program compiles but when I hit the trigger his form loads up for maybe half a second and then closes. Does anyone know what I am doing wrong?
You have almost get it right. This is because the RAII of C++. If you allocate the Dialog on stack, it would be destructed as soon as the function return.
Assuming MainWindowImpl inherits publically from QWidget, you're looking for this:
void MainWindowImpl::add_rec()
{
// passing "this" to the constructor makes sure dialog will be cleaned up.
// Note that DialogImpl will need a constructor that takes a
// QObject* parent parameter.
DialogImpl* dialog = new DialogImpl(this);
dialog->show();
}
Look at the Qt documentation for examples of how the constructors should look.
Apparently QT4 only allows one instance of an object at a time, however pointers are another matter. Change both the main.cpp and what ever your main window to look something like this:
DialogImpl *dia=new DialogImpl;
dia->show();