Qt C++，将 class 实例信号连接到 Widget 主 class

Question

My code contains a function which takes a lot of time to compute. To make it feel more responsive, I wanted to visualize every tenth of the progress with a progress bar. However, the function is implemented in another class other than my Main Widget class and I cannot access the ui elements of the Widget class. I tried putting a signal which can be emitted during the function, however it comes up as an error. The relevant code looks like this:

//Class cpp implementation
void Dataset::calculateNew(){

for(int i = 0; i<1000; i++){
     if(i%100==0)
       emit valueChanged(i);  //first Error
        for(int j = 0; j<1000; j++){
            for(int k=0; k<1000; k++){

             //Expensive Matrix calculation
        }
     }
  }
} 

//Class .h implementation

signal:
valueChanged(int value);

//Widget implementation
 
connect(Dataset::calculateNew(), SIGNAL(valueChanged(int)), this, SLOT(updateProgressBar(int))); //second Error here
 

Am I thinking in the right way? What should I do to make it work? Or is there another way to access and change ui Elements of the Widget class.

Note: I tried including the "widget.h" in Dataset class, but it isn´t recognized as a class to be included,

Answer 1

Hard to say without the minimal example, but I guess the problem lies in your call to connect:

connect(Dataset::calculateNew(), SIGNAL(valueChanged(int)), this, SLOT(updateProgressBar(int))); //second Error here

Provided your dataset object is called ds , it should look like this: connect(&ds, SIGNAL(valueChanged(int)), this, SLOT(updateProgressBar(int)));

BTW, why don't you use the new signal-slot syntax based on fucntion pointers? Are you still on QT4?

Answer 2

Don't use these old signals. Use the new

connect(datasetPotr, &Dataset::valueChanged, this,&thisClassObject::updateProgressBar);

Also, this will destroy your loop performance. Because you will push update on each tick & force redraw in loop thread. You should look in to more complex system of notification... Say notify every xx int values, so from 0- 100 do every 10, so you do 10% increments. Etc etc.