从多个上传的文件中获取文件名

I have 4 fileupload in my form. I want when I click a button, I get the file name and set to model, then the file upload to server. But i don't want must use 4 file, I can use 3, 2, or 1 file upload at a time by choice. If I only use 2 file upload, file3 and file4 model still null. what I must do in my controller ? in my form. I want when I c