Getting a new variables from a function-CodePudding

I have 3 files

Main which contains a function call when the application is launched

void main() async { 
  await FunctionCall().numberColumnFunction();
  runApp(const MyApp());
}

Function in which the called function and variables are located:

class FunctionCall {
    
  int numberColumn = 3;

  int columnsPositioned = 5;
  var visibilityColumn = false;

    numberColumnFunction(){
      if (numberColumn == 3) {
        columnsPositioned = 8;
        visibilityColumn = true;
      }
      else {
        null;
      }
    }
}

And ColumnView in which I get variables from the Function for further work with them:

// More code
     end: width / FunctionCall().columnsPositioned,
// More code
     visible: FunctionCall().visibilityColumn,
// More code

The problem is that in ColumnView the variables declared by me with default values are always called

  int columnsPositioned = 5;
  var visibilityColumn = false;

Even if the function conditions are met and the values in the variables change, the call still goes to the old values. How do I make ColumnView take values after executing the function ?

CodePudding user response：

The traditional and programming way I can think of right now is making that class a singleton. You can search and do more research on singleton classes and factory pattern. But for now, this code should solve your problem ->

class FunctionCall {
 FunctionCall._sharedInstance(); //This is a private constructor. 
 static final FunctionCall _shared = FunctionCall._sharedInstance(); // This is the instance we want to send every time.
 factory FunctionCall() => _shared; // This is where we send it every time the class is created!

 int numberColumn = 3;
 int columnsPositioned = 5;
 var visibilityColumn = false;

numberColumnFunction(){
  if (numberColumn == 3) {
    columnsPositioned = 8;
    visibilityColumn = true;
  }
  else {
    null;
    }
  }
}

Basically, the problem was, Every time you called the class like this FunctionCall() It was creating a new class. And a new class would always have the default class data. Bcz the function didn't get called inside the new class. So to stop making a new instance of your class you can try this way of making your class a singleton. And returning the exact same instance of your class when it is initiated! And Done!

CodePudding user response：

You are creating the FunctionCall() object inside the main function. The Visibility Column for this object is true. However, you are creating a new FunctionCall() object inside the ColumnView widget. The visibilityColumn value of this object is initially set to false. They are two different objects.

My suggestion:

FunctionCall functionCall = FuncitonCall();

Define the above code globally. Edit this object in main and use the same object in ColumnView widget.