Android's ExifInterface only lets you write exif tags that are "recognized." You can find SOME of the recognized exif tags in the link: http://developer.android.com/reference/android/media/ExifInterface.html
But the good news is, there's more exif tags that's not mentioned in the Android API.
Bad news is, I still haven't found a library that lists all usable exif tags
After researching and experimenting for hours, I found that the following tag works:
"UserComment"
So the following code snippet will work:
String mString = "Your message here";
ExifInterface exif = new ExifInterface(path_of_your_jpeg_file);
exif.setAttribute("UserComment", mString);
exif.saveAttributes();
I'm still trying to find out which other exif tags are allowed, but for now, this should do the trick.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…