Four methods of closing forms in C ＃

1. close()：
   Close only the current form , If it's not the main form （ Form containing the main thread , Is not MDI forms ） Words , You can't exit the whole program . If there is a managed thread, it cannot exit .
     This method calls dispose() Method , So it will automatically help us free memory , Except for the following two cases ：（1） This form is a multi document application （MDI） And this form is not visible ;（2） This form is “ Modality ” forms .
     close() Two events will be triggered when the method is executed ：Form_Closing and Form_Closeed event ,Form_Closing Is executed when the form is closed ,Form_Closed Is executed after the form is closed , So if you want to cancel closing the form , Can be in Form_Closing Cancel... In the event .

2. Application.Exit()：
   Force all messages to abort , Exit all forms , But if there are managed threads （ Non main thread ）, And you can't exit cleanly .

3. Application.ExitThread()：
   Force all messages on the calling thread to abort , It also faces the problem that other threads cannot exit correctly .

4. System.Environment.Exit(0);
   This is the most radical way out , No matter what thread is forced to exit , Clean the end of the program . Parameters 0： Represents the normal exit of the program ; Parameters 1： Represents the abnormal exit of the program .