CODEWITHSUNDEEP
c++qt
erbal
erbal

Reputation: 727

New window doesn't show

I have a button, when it is clicked a new window show with a QLineEdit, and a QLabel on it, my connection between the button and the function works fine, but the new window doesn't show.

void windowManager::addQuestionDialog(){
    QWidget window(&parent);
    QLineEdit question;
    QLabel label;
    QVBoxLayout layout;

    layout.addWidget(&question);
    layout.addWidget(&label);
    window.setLayout(&layout);
    window.resize(200,200);
    window.setWindowTitle(QObject::trUtf8("Kérdés bevitele..."));
    window.show();

}

Upvotes: 2

Views: 144

Answers (2)

totymedli
totymedli

Reputation: 31078

You need to create class tag variables for the new window and the stuff you want to put into it, than create the objects themselves with the new keyword in the function, because if you create all of these simply in a function, than they will created in the stack, and you should know that after a function returns/finishes, the stack to that function is deleted (with your new window and the stuff on it too).

Include the headers for the classes you want to use in your windowManager header file:

#include <QDialog>
#include <QLineEdit>
#include <QLabel>
#include <QVBoxLayout>

Then add the tag variables to the private part:

private:
    QDialog *window;
    QLineEdit *question;
    QLabel *label;
    QVBoxLayout *layout;

In your button's click event set the tag variables, and create the UI setup:

void windowManager::addQuestionDialog()
{
    window = new QDialog();
    question = new QLineEdit();
    label = new QLabel();
    layout = new QVBoxLayout();
    layout->addWidget(question);
    layout->addWidget(label);
    window->setLayout(layout);
    window->resize(200,200);
    window->setWindowTitle(QObject::trUtf8("Kérdés bevitele..."));
    window->show();
}

Also don't forget that you should use -> instead of . for calling functions here, because these tag variables are pointers. Also that's the reason why you don't need to use the & operator to get their address.

Also keep in mind that you should delete these objects, because C++ doesn't delete these automatically for you. You should delete everything you new. A good place to do this is in the destructor in your windowManager class. Just check if the tag variables are not NULL (if there is an object) before you try to delete them, otherwise errors may occur.

A better solution is to pass a parent pointer as the constructor's parameter, so this way Qt will delete them as they are closed, because if the parent is destroyed, the children will be destroyed too.
As an extra, you don't have to set manually where does the objects are go, because Qt will now it from the hierarchy (in some cases).

In this case your button's click event function would look like this:

void windowManager::addQuestionDialog()
{
    window = new QDialog(this);
    question = new QLineEdit(window);
    label = new QLabel(window);
    layout = new QVBoxLayout(window);
    //The following two lines are optional, but if you don't add them, the dialog will look different.
    layout->addWidget(question);
    layout->addWidget(label);
    window->resize(200,200);
    window->setWindowTitle(QObject::trUtf8("Kérdés bevitele..."));
    window->show();
}

Upvotes: 2

BartoszKP
BartoszKP

Reputation: 35891

You create the window QWidget object on the stack. Therefore, this object will be deleted when the call to the function addQuestionDialog finishes. Change the code to create the new window widget using "new", and arrange it to be deleted after it was closed. Some possible solutions are presented here:

destructors in Qt4

Upvotes: 0

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