Monday, February 10, 2014

Guarding enumeration classes from ProGuard

During my application tests I received exception with the following call stack:
02-09 15:18:06.478 26166 26403 E TAG: Caused by: java.lang.NullPointerException
02-09 15:18:06.478 26166 26403 E TAG:   at java.lang.Enum$1.create(
02-09 15:18:06.478 26166 26403 E TAG:   at java.lang.Enum$1.create(
02-09 15:18:06.478 26166 26403 E TAG:   at libcore.util.BasicLruCache.get(
02-09 15:18:06.478 26166 26403 E TAG:   at java.lang.Enum.getSharedConstants(
02-09 15:18:06.478 26166 26403 E TAG:   at java.util.EnumSet.noneOf(
02-09 15:18:06.478 26166 26403 E TAG:   at af.a(SourceFile:115)
The exception occurred only in release version, while in debug everything worked fine. So I immediately suspected that ProGuard, whose processing is part of a release build, is somehow involved here.

From ProGuard's documentation:
If your application, applet, servlet, library, etc., contains enumeration classes, you'll have to preserve some special methods. Enumerations were introduced in Java 5. The java compiler translates enumerations into classes with a special structure. Notably, the classes contain implementations of some static methods that the run-time environment accesses by introspection (Isn't that just grand? Introspection is the self-modifying code of a new generation). You have to specify these explicitly, to make sure they aren't removed or obfuscated: 
-keepclassmembers,allowoptimization enum * {
      public static **[] values();
      public static ** valueOf(java.lang.String);
OK, problem found: I just need to add this 'keepclassmembers' exception in ProGuard project configuration file.

But what are values() and valueof(java.lang.String) needed for? I still was curious how exactly I received NullPointerException in java.lang.Enum entrails. Let's better understand it.

Monday, February 3, 2014

Programmatically filtering your application's logs from Logcat output

Note: this post discusses filtering Logcat output on devices running Android prior to version 4.1. Starting from Android 4.1 applications are allowed to read only their own logs.

Logcat isn't much convenient when it comes to filtering your application logs. In fact, if you look at the logcat documentation, you will find that you can filter logcat output only by priority and/or tag fields:
A filter expression follows this format tag:priority ..., where tag indicates the tag of interest and priority indicates the minimum level of priority to report for that tag. Messages for that tag at or above the specified priority are written to the log. You can supply any number of tag:priority specifications in a single filter expression. The series of specifications is whitespace-delimited.
The android.util.Log class is your interface for printing your application logs to the Logcat system. Common print statement looks like this:
Log.e(TAG, "something bad happened");
Invoked method specifies the priority of the log record - in this example e stands for error, and TAG specifies well.. the tag.
 I commonly set the class name as a TAG using this statement:
private static final String TAG = ClassName.class.getCanonicalName();
Resolving the class name at run-time allows me to stay flexible and be adjusted to all the obfuscations made by Proguard processing.

But here's a problem: given a project with a hundred classes, how would you filter Logcat's output to print just your application's logs?

Saturday, February 1, 2014

Solving errors in Android Studio's new project creation

The other day I upgraded my Android Studio bundle to latest stable version: android-studio-bundle-132.893413-windows.

Shortly afterwards, I noticed that each time I tried to create a new project, it ended with the following error message:
Cause: error in opening zip file. Consult IDE log for more details (Help | Show Log)

Hmmmm.. which error file exactly and what's wrong with it?