How to set value to a variable in QtObject::connect

ARASHz4

Hi i want set value to a variable in a connection
this my code but don't work

float size; 
connect(GFS, SIGNAL (completed(float)), size = float);

Is this possible?

J.Hilk

@ARASHz4
hi,

yes, what you try to do can be done in QT, take a look at Lambda expressions in c++11 in here

In the article you should find everything you need to make your code-example work :-)

gl!

BePie

But where is the "size" ?
Is it a member of a class that is QObject? If yes- the fastest way is to use lambda
like this

// code somewhere inside a scope of the QObject instance
connect(sender, &Sender::someFloatDataChanged, [=](float newData) {
  this->a = newData;
});

ARASHz4

i do this before like this :

connect(GFS, SIGNAL (completed(float)), this, SLOT (setSize(float)));

completed signal have value & slot setSize get this value but i want set this value to a variable

J.Hilk

@ARASHz4

@BePie more or less showed you how exactly to do it.

But here again:

First your variable to store/hold the data must either be declared in your header or in the function where you make the QObject::connect();

float mySize;

than adjust your connect statement, first part - Pointer to Object and Signal - stays the same as always.

connect(GFS, &myGfsClass::completed,
...

than comes the lambda fuction in {}-brackets + correct syntax for your variable, the float from the completed SIGNAL.

...
[=](float value){mySize =value;});

and done.

BePie

so w/o explicit slot creation you can write:

connect(GFS, &GFS_T::completed, [=](float newData){setSize(newData);}));

where GFS_T is a type of GFS
or paste code from setSize() to the body of the lambda

ARASHz4

@BePie thank you but GFS is type of a class

FileSize *GFS;

BePie

so you write

connect(GFS, &FileSize::completed, [=](float newData){setSize(newData);}));

so &FileSize::completed is a reference to signal-function of type (class) FileSize
the last argument is a lambda with copy ([=]) scope that takes one float (must match FileSize::completed arguments) and invokes setSize (implicitely of "this" pointer that is copied ([=])) with passed argument from signal.
I am not sure that I am 100% correct, I am not a pro lambda user. For more info check out some lambda tutorials.

but FileSize has to inherit from QObject (otherwise signal-slots won't magically work :P)

// edited: QOpenGL->QObject and added some notes