I'm working on a QT project. I was wondering if is possible to create a connection using two signals to execute a method.

I have three classes: A, B and C. Class A emit a signal when a button is pressed (connected in Class C), also in Class C a QProcess is created (from an instance of class B).

In class C I have a connect to get the output of the QProcess. Also, I have another connect to execute a method when a button is pressed (signal emitted in Class A).

So, I need to modify the current behavior, the doSomething() method should be executed when the QProcess output is ready, similar to an if statement:

if(signalA && signal B){
  do something...
}

This is the current code:

//This signal will get the output of a Qprocess
connect(objectC,&QProcess::readyReadStandardOutput, [=] (){
    QString out = objectB->readAllStandardOutput();
    qDebug() << out;
});

//When a button in Class A is pressed doSomething() is executed
//but now I must wait until the above signal generates an output.
connect(objectA, ClassA::buttonPressed, [=] (){
    doSomething();
});

objectC -> run(args); // This line execute an external process

any Ideas on how to achieve this?

I found on stackoverflow that in QT we can have two signals in a single connect, like this:

connect(this,SIGNAL(someSignal()),this,SIGNAL(anotherSignal()));

but I don't know how to adapt this to my problem.

The flow of my QT application is the following:

• A QProcess is created to launch an external .exe file

• The QProcess return a QString

• At any moment the user can press a button that will execute a specific method (doSomething()) but needs the output of the QProcess.

• The big issue is that sometimes the user press the button before the QProcess ends, so I cannot execute the doSomething() correctly.

• The desired behavior is: if the user press the button to execute doSomething(), first I must wait until the output of the QProcess is ready. So if I press the button and if the QProcess takes e.g 10s to finish, the doSomething() should be executed after this 10s.

CodePudding user response：

You can store the state of both events and check them both whenever one of them changes.

// These should probably be defined in the header of your class.
bool processFinished = false;
bool buttonClicked = false;

void checkState() {
    if (buttonClicked && processFinished) {
        doSomething();
    }
}

connect(objectC,&QProcess::readyReadStandardOutput, [=] (){
    ...
    processFinished = true;
    checkState();
});

connect(objectA, ClassA::buttonPressed, [=] (){
    ...
    buttonClicked = true;
    checkState();
});