How to pass values between forms in c# windows application?

Question

I have two forms A and B. Form A is the default start up form of the application. I do some stuffs in Form A and i then i want to run my Form B parallel and then pass a para

Answer 1

Depending on your needs, another approach would be to introduce a global instance of a class (a singleton), which can hold stuff that is to be shared between several forms/classes of your application.

For instance, if you have a form where the user can define his settings/preferences, you could store that data in a singleton. All other classes and forms of your application can then access/read these settings from the same singleton instance.

Here's a very basic example of a singleton:

public class MySettings
{
  // the one and only instace (the singleton):
  public static readonly MySettings Instance = new MySettings();
  private MySettings() {} // private constructor

  public int SomeNumber { get; set; }
  public string SomeString { get; set; }
}

Now you can access set/get the properties of MySetting from any other class/form in your application, e.g:

in PreferencesForm.cs:

//read the user's input and store it in the settings
MySettings.Instance.SomeNumber = txtNumber.Value;

in SomeOtherForm.cs:

//read the user's setting and use it
int theNumber = MySettings.Instance.SomeNumber;
// do something with theNumber