How to open one time new widget

asttekin

Hi all,

I want to open full screen widget one time.A new widget is opening each click .

 fs *_fs = new fs(*this, 0);
 _fs->show();

I tried this code but doesn't work.

fs *_fs = new fs(*this, 0);
    if(!_fs->isVisible())
    {
        _fs->show();
    }

? Offline

Hi! What exactly "doesn't work"? Please provide a minimal example of what you're doing, say what you expect the code to do and what it actually does for you. Btw, to show a widget in full screen mode you can use void QWidget::showFullScreen().

asttekin

 fs *_fs = new fs(*this, 0);
 _fs->show();

I used this code.But this code open a new widget every click.I want to open only one widget.How can I do that.

? Offline

Sure, because with new you create a new widget everytime

mrjj

Hi
You should move the variable into the class

class mainwin : xx {
fs *_fs=NULL; // make sure its NULL
};

then say
if (!_fs)
_fs = new fs(*this, 0);

Note its VERY IMPORTANT its set to NULL to begin with or u will crash.

raspe88

There's a design pattern called "Singleton" that describes how to deal with the issue of creating "just one instance of a class for the whole program" - mrjj already told you the most important things about how it can be implemented in C++, but you can read more about it taking a look at e.g.:

One remark regarding singleton and C++11: Since C++11 it is even possible to create a threadsafe singleton very easy:

class Singleton {
public:
    static Singleton& getInstance() {
        static Singleton instance;
        return instance;
    }
};

kshegunov

@raspe88 said in How to open one time new widget:

There's a design pattern called "Singleton"

Indeed, there is such an antipattern. But @asttekin, I ask you, I beg you, I implore you, forget it exists and never follow links leading to it! It is like the road to hell - all paved with good intentions.

jsulm

@kshegunov @raspe88 Not to mention that this antipattern is an exorbitant overhead in this case! It is really just a matter of checking whether the pointer is null or not.