The
best way to use Constructors in .NET is the way that fits the overall goal of your Application, and the overall nature of the Data you import/transform/export in the Application, like a glove fits a hand :)
Which is to say: there are many possible "correct" ways of using Constructors for Classes (or Structs).
One specific comment: you state: "A class can have private fields, public properties, constructors and methods." I'm not sure this needs saying, but: a Class can
also have public fields, and private Properties, and internal private Classes.
One thing I note in your code is that you perform validation when you set Public Properties. In one of the Public Properties, "ID," you throw an error in the case of incorrect input; in the other properties you don't.
In two cases, "Gender," and "City," you rely on .NET's automatic binding of a Property to a hidden internal variable, rather than write code for the 'set and 'get functions as you do for the other Properties.
You are the only one who can answer the questions:
1. should all the Properties be handled in the same way
2. should all the Properties throw an error if there's unexpected or incorrect input ?
3. is handling validation in the Properties the "right thing" for this Application ? if external "consumers" of your Class are changing the Properties at run-time, then the answer is almost certainly "yes."
if consumers of the Class are
never going to change the Properties, then you might consider doing validation in the Constructor; or ... elsewhere ?
The one idea I see "missing" in your code is the use of chained Constructors in .NET. Consider this excerpt ... WinForms, a UserControl ... from code I am currently working on:
public DdwnChkCombo()
{
InitializeComponent();
}
public DdwnChkCombo(string title, List<string> lvItems): this()
{
foreach (string str in lvItems)
{
dDwnListView.Items.Add(new ListViewItem(str));
}
dDwnButton.Text = title;
}
public DdwnChkCombo(string title, List<string> lvItems, int width): this(title, lvItems)
{
this.Width = width;
}
If the third ctor above is used to make a new instance of 'DdnChkCombo, the following sequence will occur at run-time:
1. the third ctor is called, but the code in its "body" is not executed: flow-of-control is passed to the second ctor.
2. the second ctor ... because the next ctor is parameterless ... will result in flow-of-control going to initialization of the private fields in the class. interestingly, this will be followed by execution of one part of the Designer.cs Class where the 'components variable is set.
3. control goes to the first ctor, and InitializeComponents in the Designer.cs file is executed which builds/lays-out the Form and its Controls.
4. then control is passed back to the second ctor, and the code in its body is executed.
5. finally, control moves to the third ctor, and the code in its body is executed.
So, you have a way of defining multiple constructors, in which you successively add more parameters, and the use of the special operator "this" after the parameter list, preceded by a colon, gives you a way to incrementally build your Classes.
Of course, there are always other ways: you could define optional parameters for a Class: but, if you do that, then you, of course, have to write some boolean tests to see if they are present, or absent.
I recommend that as you develop Classes, and experiment with inheritance, you make a habit of stepping-through your code using the debugger in Visual Studio, and observing exactly what happens as Classes are instantiated.