Two windows APIs

In the ApplicationProgramClass, there is an initinstance () function,
: In this function, assume the following two rows:
: Registershellfiletype ();
: Enableshellopen ();
Registershellfiletype () is used to allow file association. For example, notepad can open text files,
If you create a new file type, the operating system opens the file type you created with your program by default.
Enableshellopen (): When you drag a file to your program, you can open the corresponding document. Enter ie. You can open this document when you drag the document to IE.