How to import file without script?

I use RhinoApp().L"-Import …" to import file,but sometimes it will failed. So I changed "-Import" to “Import" and it works.
But it will show a dialog after I changed "
-Import” to “Import". But I don`t want to show the dialog.
First I want to know what different between "
-Import” and “_Import”?
Second it there any possible to find a generic function that will allow to import all file types in Rhino?

As each type of file, support by Rhino for opening or importing, has a different set of options, it not possible to write a single, generic file open function and hope to support all formats. Thus, if you want to open or import a file from a plug-in command, then simply script either Rhino’s Open or Import command.

Note, Note, in case the file name string contains spaces, we will want to surround the string with double-quote characters so the command line parser will deal with the string property.

Here is an example in C++:

I want to know what different between _-Import and Import when use RhinoApp().runscript?
These two commend both can import file successfully,but _-Import will fail when I use my commend on a new computer.
After I use Rhino to import file successfully, _-Import won`t fail again.