closing a dialog

[chrisb123]

I made a plasma app that opens a settings dialog
I'm trying to close a dialog with a close button
If I open it like this

void test::settings() { 
 myQtApp *dialog = new myQtApp;
 dialog->show();
}

void test::settings() { 
 myQtApp *dialog = new myQtApp;
 dialog->show();
}

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How can i close it like this

myQtApp::myQtApp(QWidget *parent)
{
    setupUi(this);
    connect( pushButton_close, SIGNAL( clicked() ), this, SLOT( close() ) ); 
}
void myQtApp::close() {
  QMessageBox::about(this,"close",
  "this shold close the dialog");
}

myQtApp::myQtApp(QWidget *parent)
{
    setupUi(this);
    connect( pushButton_close, SIGNAL( clicked() ), this, SLOT( close() ) ); 
}
void myQtApp::close() {
  QMessageBox::about(this,"close",
  "this shold close the dialog");
}

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[axeljaeger]

First, you are leaking memory because you create a QDialog on the heap without a proper parent. Don't do this, read something about object trees in Qt:

http://doc.trolltech.com/4.5/objecttrees.html

Then remove your own implementation of close because there is already one in QDialog. I am pretty sure that you showing your message box, you overwrite the already provided close-slot.

[chrisb123]

i found out if use

this->hide();

this->hide();

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it will close, however I should delete the close function
Sorry my programming skills are limited, I still dont quite understand
I do a lot of copy, paste, modify with-out understanding whats really going on
If I remove the "QWidget *parent" is that better?
The application still works as expected

[squidge]

If you don't use parent you should use a model dialog so you can delete the dialog when the model returns

[chrisb123]

Don't you just hate crappy programmers like me...
I have a

target::target(QObject *parent, const QVariantList &args)
    : Plasma::Applet(parent, args),

target::target(QObject *parent, const QVariantList &args)
    : Plasma::Applet(parent, args),

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it contains parent, again, which I don't understand.

[axeljaeger]

The point is:

You usually create a tree of objects. If you delete an object, all its childs are deleted as well. So usually you do not have to care about deleting most of the objects because they will be deleted by their parent object.

Also if you create an object on the stack (without new and not as a pointer) it will be deleted when going "out of scope", e.g. when the program goes out of the "block" in which the object was created.

Your dialog was not created on the stack but on the heap, it did not got a parent pointer and you do not delete it yourself. So it will not be deleted at all.

I'm a bit picky about this because at some other forum, a lot of people completely ignoring this fundamental feature of Qt. So everytime I see someone now who does not use proper parent child, some red lights turn on here.

[chrisb123]

I understand I should be correctly creating child objects of the parent
I dont understand how do write code so the object is a child of the parent
Like I said I barely understand what I'm doing
is there another tutorial I can read relating to this?

[axeljaeger]

Pass some other QWidget as the first argument to the constructor of myQtApp.
e.g not myQtApp but myQtApp(this).

[chrisb123]

doing this

myQtApp::myQtApp(this)

myQtApp::myQtApp(this)

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i get the error
expected unqualified-id before 'this'

[axeljaeger]

No no, like this:

void test::settings() { 
 myQtApp *dialog = new myQtApp(this);
 dialog->show();
}

void test::settings() { 
 myQtApp *dialog = new myQtApp(this);
 dialog->show();
}

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But you see that everytime you call the settings slot, a new instance is created and only released when you delete "this". Do it rather like this:

void test::settings() { 
 myQtApp dialog(this);
 dialog.show();
} // dialog is deleted now.

void test::settings() { 
 myQtApp dialog(this);
 dialog.show();
} // dialog is deleted now.

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[chrisb123]

neither work
i need to change the header, to what i have no idea

[chrisb123]

I dont get it ??? I'm lost

So I should not open a new dialog like this

void test::web() {
 QWidget *web = new webapp();
  web->show();

void test::web() {
 QWidget *web = new webapp();
  web->show();

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and adding a webkit widget to this new dialg like this is incorrect

webapp::webapp(){
   QWebView *view = new QWebView(this);
   view->show();
}

webapp::webapp(){
   QWebView *view = new QWebView(this);
   view->show();
}

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[RSX]

I made a plasma app that opens a settings dialog
I'm trying to close a dialog with a close button
If I open it like this

void test::settings() { 
 myQtApp *dialog = new myQtApp;
 dialog->show();
}

void test::settings() { 
 myQtApp *dialog = new myQtApp;
 dialog->show();
}

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How can i close it like this

myQtApp::myQtApp(QWidget *parent)
{
    setupUi(this);
    connect( pushButton_close, SIGNAL( clicked() ), this, SLOT( close() ) ); 
}
void myQtApp::close() {
  QMessageBox::about(this,"close",
  "this shold close the dialog");
}

myQtApp::myQtApp(QWidget *parent)
{
    setupUi(this);
    connect( pushButton_close, SIGNAL( clicked() ), this, SLOT( close() ) ); 
}
void myQtApp::close() {
  QMessageBox::about(this,"close",
  "this shold close the dialog");
}

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Didn't read up all if you actually fixed your problem already but:

myQtApp *dialog = new myQtApp(this);
dialog->setAttribute(Qt::WA_DeleteOnClose);
dialog->show();

myQtApp *dialog = new myQtApp(this);
dialog->setAttribute(Qt::WA_DeleteOnClose);
dialog->show();

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this would solve your problem with deleting dialog.

[chrisb123]

Didn't read up all if you actually fixed your problem already but:

myQtApp *dialog = new myQtApp(this);
dialog->setAttribute(Qt::WA_DeleteOnClose);
dialog->show();

myQtApp *dialog = new myQtApp(this);
dialog->setAttribute(Qt::WA_DeleteOnClose);
dialog->show();

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this would solve your problem with deleting dialog.

That works but how do I test if dialog has been deleted or not, I only want to have one created at any one time

[jano_alex_es]

I think it's deleted when you close the dialog. Qt uses to do a lot of hard work for you

Well, if so, you can delete it manually.

myQtApp *dialog = new myQtApp(this);
dialog->setAttribute(Qt::WA_DeleteOnClose);
dialog->show();
delete dialog;
dialog = 0;

myQtApp *dialog = new myQtApp(this);
dialog->setAttribute(Qt::WA_DeleteOnClose);
dialog->show();
delete dialog;
dialog = 0;

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What I do is to create the dialog on the stack. So it will be deleted for sure when it's out of scope. But I do it with small and temporary dialogs.

myQtApp dialog(this);
dialog.setAttribute(Qt::WA_DeleteOnClose);
dialog.show();

myQtApp dialog(this);
dialog.setAttribute(Qt::WA_DeleteOnClose);
dialog.show();

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[chrisb123]

My application is a plasma widget so 99.99% of the time its just the one widget, there is no reason to have anything else just waiting, hidden, invisible or not shown.

When I use this code

m_setapp = new SetApp(this);

m_setapp = new SetApp(this);

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I get this error while compiling

mum.cpp: In member function 'void mum::settings()':
mum.cpp:75: error: no matching function for call to 'SetApp::SetApp(mum* const)'
myqtapp.h:34: note: candidates are: SetApp::SetApp(QWidget*)
myqtapp.h:29: note:                 SetApp::SetApp(const SetApp&)

mum.cpp: In member function 'void mum::settings()':
mum.cpp:75: error: no matching function for call to 'SetApp::SetApp(mum* const)'
myqtapp.h:34: note: candidates are: SetApp::SetApp(QWidget*)
myqtapp.h:29: note:                 SetApp::SetApp(const SetApp&)

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But this works ok

m_setapp = new SetApp(NULL);

m_setapp = new SetApp(NULL);

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From what I can tell it's not deleted when it's closed, I have to manually delete it when its closed, then create it again when required

[axeljaeger]

Right, you have to delete it yourself when you close the application.

But again: Dont try to be to clever. Get your application up and running and dont bother too much in saving memory when you are not know what you are actually doing. Keeping the dialog in memory will not hurt very much. I'd keep it there so it gets shown faster the second time I open it.

[chrisb123]

thanks for your help, its been useful
I still need to learn c++ as object oriented programming is new to me
As for my application, it does what is needed thats why Ive moved onto improving it