My .gitattributes has the following in order to diff the XCode project (which is plain text)
*.pbxproj -crlf -diff -merge
But when I diff, still showing binary file
# git diff MyApp.xcodeproj/project.pbxproj
diff --git a/MyApp.xcodeproj/project.pbxproj b/MyApp.xcodeproj/project.pbxproj
index xxx..xxx xxx
Binary files a/MyApp.xcodeproj/project.pbxproj and b/MyApp.xcodeproj/project.pbxproj differ
My .gitattributes is in the same level of .git folder
Correct. Your .gitattributes is saying to treat the file as binary when it comes to diffing and merging. Take a look at this StackOverflow question, which is awfully similar to yours: Git and pbxproj