Android ProGuard +MultiDex causes ClassNotFoundException

Question

I have `MultiDex` enabled in my android project. It was working fine until I tried enabling proguard. I can successfully build the project but I get runtime exception on startup. It's unable to find the Application class and the `MainActivity`. I had the same problem before enabling `MultiDex`. Now I guess for some reason the `MultiDex` is not working properly with `ProGuard`. Here is what i get in the logcat - ``` 02-17 19:01:09.749: I/MultiDex(2079): VM with version 2.1.0 has multidex support 02-17 19:01:09.749: I/MultiDex(2079): install 02-17 19:01:09.749: I/MultiDex(2079): VM has multidex support, MultiDex support library is disabled. 02-17 19:01:09.750: I/art(2079): Rejecting re-init on previously-failed class java.lang.Class 02-17 19:01:09.750: I/art(2079): Rejecting re-init on previously-failed class java.lang.Class 02-17 19:01:09.751: I/art(2079): Rejecting re-init on previously-failed class java…

Accepted Answer

This page says:

The default `proguard.cfg` file tries to cover general cases, but you might encounter exceptions such as `ClassNotFoundException`, which happens when ProGuard strips away an entire class that your application calls.

You can fix errors when ProGuard strips away your code by adding a `-keep` line in the `proguard.cfg` file. For example:

```
-keep public class <MyClass>
```

There are many options and considerations when using the -keep option, so it is highly recommended that you read the ProGuard Manual for more information about customizing your configuration file. The Overview of Keep options and Examples sections are particularly helpful. The Troubleshooting section of the ProGuard Manual outlines other common problems you might encounter when your code gets stripped away.

Solution 1

You could try the following `proguard.cfg` I used to obfuscate the code while not optimising, and hence not remove classes/methods from your APK.

```
-dontusemixedcaseclassnames
-dontskipnonpubliclibraryclasses
-dontpreverify
-dontoptimize
-verbose
```

Solution 2

You have asked some classes to be kept but not for `MainActivity`. So you have to add this line:

```
-keep class com.mypackage.activities.MainActivity { *; }
```

Android ProGuard +MultiDex causes ClassNotFoundException

Solution

Problem