android-with-emacs

Notes and code for using Emacs for Android development.

Below I've added elisp code you can add to your .emacs file for M-x compile support with emacs. The code provides the following features:

• Gradle build support
• Recognize compilation errors (jump to errors with M-x `

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; M-x compile support
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(require 'cl)

;; Helper function to find files. Source: emacswiki
(defun* get-closest-pathname (&optional (file "Makefile"))
  "Determine the pathname of the first instance of FILE starting from the current directory towards root.
This may not do the correct thing in presence of links. If it does not find FILE, then it shall return 
the current directory"
  (let ((root (expand-file-name "/")))
    (loop for d = default-directory 
          then (expand-file-name ".." d)
          if (file-exists-p (expand-file-name file d))  return d
          if (equal d root) return nil)))

;; Tries to locate the gradlew wrapper, and if found create and return
;; a "make" string which changes into that directory and executes ./gradlew
;; with assembleDebug by default.
;;
;; How to recognize compilation errors.
;; For some reason, the errors returned when compilation is run from within emacs is:
;;   :TournmanApplication:compileRelease/home/marius/p/tournman/android/workspace/TournmanProject/TournmanApplication/src/main/java/net/kjeldahl/tournman/TournmanActivity.java:153: error: ';' expected
;;
;; This regexp captures the filename and line number by looking for ":compile.*?(filename):(lineno):
(require 'compile)

(defun gradleMake ()
  (unless (file-exists-p "gradlew")
    (set (make-local-variable 'compile-command)
         (let ((mkfile (get-closest-pathname "gradlew")))
           (if mkfile
               (progn (format "cd %s; ./gradlew assembleDebug"
                              mkfile))))))
  (add-to-list 'compilation-error-regexp-alist '(":compile.*?\\(/.*?\\):\\([0-9]+\\): " 1 2)))

(add-hook 'java-mode-hook 'gradleMake)

If you're curious about the non-lispy looking code inside the "loop" form inside the get-closest-pathname function, it's a ported cl (common lisp) macro. You can read more about it at http://www.gigamonkeys.com/book/loop-for-black-belts.html.

Automatic compile, install and execute on connected device

In addition to generic "./gradlew assembleDebug" support which the code above demonstrates, you can also have customized compilation/build commands for individual projects and/or file. In my own projects I typically have the following at the end of my main activity source file ("MainActivity.java") that takes care of building, installing and executing the build on a connected device or emulator:

// Emulator startup: emulator -avd Dev41 -scale 0.5 -prop debug.assert=1
//
// Local Variables:
// compile-command: "cd /home/marius/p/tournman/android/workspace/TournmanProject/; ./gradlew assembleDebug && adb install -r TournmanApplication/build/apk/TournmanApplication-debug-unaligned.apk && adb shell \"am start -n net.kjeldahl.tournman/.TournmanActivity\""
// End:

Auto-complete and searching imports

I haven't find a really simple setup yet; there are many ways. Unfortunately the documentation for how do to this with Emacs is almost non-existent. But I have something that should be fairly simple to get started with, at least if you are using emacs24 (which I am). First you need to install the auto-complete and ggtags packages. The auto-complete package seem to offer auto complete for both local symbols (defined in your source code) and some import classes, but I am not sure exactly how it figures out that I'm using Android, and where my Android sources/jars are located.

The ggtags package is an interface to the GNU Global package for navigating source code, which you also need to install. On Ubuntu, you can do this using sudo apt-get install global. After installing, navigate to your project root and create links to any other source directories you would like indexed. You can put these links in a separate subdirectory; the gtags program (which is installed when you installed global), searches for sources in all subdirs. For android development I've created a "libsrc" directory, where I have a symlink to /opt/android-studio/sdk/sources/android-18/. With this in place, just execute gtags in your project root and the program will create the files GTAGS, GSYMS and GRTAGS in your project root. These are index files used for looking up source code references. The global system can be used from the command line, for instance execute global Activity in your project and it will show you references to the Android source where the class gets defined and used.

More interestingly, with the ggtags package installed you can do this from within emacs. If you load up a java source file from your project, move the cursor or write Activity somewhere, and then press M-., it will open up two buffers; one which shows the same references that it showed when you executed global from the command line, and in the other it will open up the actual first file. In this case this is the Android source code for the implementation of Activity. M-* will close these windows again, while M-{ and M-} will navigate to the next/previous mention of Activity (for this search). From this, figuring out the correct import to put in place is easy (move to the top of the file or look at the buffer file name). While not as easy as pressing a magic button to get an import statement generated and put into your source code file, it is possibly more useful as it allows you to easily get to both the docs and source code easily.

Ah, I almost forgot, as with most things emacs, you may have to add some stuff to your .emacs file. Here's what I have in mine which seems to work fine:

(require 'ggtags)
(autoload 'ggtags-mode "ggtags" "" t)
(setq gtags-suggested-key-mapping t)
(global-set-key (kbd "C-c C-f") 'gtags-find-file)

(require 'auto-complete-config)
(ac-config-default)
(setq ac-ignore-case 'smart)
(setq ac-use-menu-map t)
(setq ac-source-gtags)
(define-key ac-menu-map "\C-n" 'ac-next)
(define-key ac-menu-map "\C-p" 'ac-previous)