C# – Separation of concerns for a “Manager” class

cdesign-patternsseparation-of-concernssolid

I have a Class that "controls" the current application state, ApplicationStateManager.
I have an Enum that lists the possible states for the application

enum ApplicationState
{ 
    Idle,
    Starting,
    Started,
    Stopping,
    Stopped
}

ApplicationStateManager contains members such as:

public static ApplicationState CurrentState = ApplicationState.Idle;

public static void ChangeCurrentState(ApplicationState newState)
{
      CurrentState = newState;
}

I could query the CurrentState static field by using ApplicationStateManager.CurrentState; to see if I can continue code execution or something along these lines.

Now the question is I was trying to separate concerns by having an ApplicationStateChanger but the problem is, where to stick the CurrentState variable?

Best Answer

If the behavior of your application depends on the state it is in, then this is a clear indicator that you might want to implement it as a Finite State Machine.

This can be achieved using State Pattern or Visitor Pattern. You should use former if the number of states is prone to change more often, and the latter if the number of events that can trigger state change is prone to change more often.

Related Solutions

C# Design – Class Design and Separation of Concerns

If the logic needed to save the data differs depending on what's being shown in the lists, you should have the controller handle saving the lists. The code you've shown seems to be for your view, so all it should worry about is displaying the lists and shouldn't need to know what's actually in them. Let the controller figure out what type of data is in the 2 lists and what the appropriate save logic would be.

Separation of Concerns – When is it Too Much

Your various examples of splitting out concerns into separate functions all suffer from the same issue: you are still hard-coding the file dependency into get_last_appearance_of_keyword. This makes that function hard to test as it now has to reply on a file existing in the file system when the test is run. This leads to brittle tests.

So I'd simply change your original function to:

def get_last_appearance_of_keyword(text, keyword):
    line_number = 0
    for line in text:
        if keyword in line:
            line_number = line
    return line_number

Now you have a function that has just one responsibility: find the last occurrence of a keyword in some text. If that text is to come from a file, that becomes the caller's responsibility to deal with. When testing, you can then just pass in a block of text. When using it with runtime code, first the file is read, then this function is called. That is real separation of concerns.

Best Answer

Related Solutions

C# Design – Class Design and Separation of Concerns

Separation of Concerns – When is it Too Much

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