I'm experiencing this crash when using proguard after integrating the NavigationComponent (android.arch.navigation:navigation-fragment-ktx:1.0.0-alpha01) into my project with target and compile sdk of 27
2018-05-16 12:13:14.044 24573-24573/com.mypackage.myapp.x E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.mypackage.myapp.x, PID: 24573
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mypackage.myapp.x/com.mypackage.myapp.MainActivity}: android.view.InflateException: Binary XML file line #16: Binary XML file line #16: Error inflating class fragment
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2925)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3060)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:110)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1800)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6649)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:826)
Caused by: android.view.InflateException: Binary XML file line #16: Binary XML file line #16: Error inflating class fragment
Caused by: android.view.InflateException: Binary XML file line #16: Error inflating class fragment
Caused by: java.lang.RuntimeException: Exception inflating com.mypackage.myapp.x:navigation/nav_graph line 7
at androidx.navigation.j.a(Unknown Source:124)
at androidx.navigation.d.a(Unknown Source:4)
at androidx.navigation.fragment.NavHostFragment.a(Unknown Source:88)
at android.support.v4.app.Fragment.l(Unknown Source:15)
at android.support.v4.app.m.a(Unknown Source:369)
at android.support.v4.app.m.b(Unknown Source:7)
at android.support.v4.app.m.a(Unknown Source:74)
at android.support.v4.app.m.onCreateView(Unknown Source:216)
at android.support.v4.app.j.a(Unknown Source:4)
at android.support.v4.app.h.a(Unknown Source:2)
at android.support.v4.app.d.onCreateView(Unknown Source:0)
at android.support.v4.app.h.onCreateView(Unknown Source:0)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:780)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:730)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:863)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:824)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:866)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:824)
at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
at android.support.v7.app.AppCompatDelegateImplV9.b(Unknown Source:23)
at android.support.v7.app.d.setContentView(Unknown Source:4)
at com.mypackage.myapp.MainActivity.onCreate(Unknown Source:12)
at android.app.Activity.performCreate(Activity.java:7130)
at android.app.Activity.performCreate(Activity.java:7121)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1262)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2905)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3060)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:110)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1800)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6649)
at java.lang.reflect.Method.invoke(Native Method)
2018-05-16 12:13:14.044 24573-24573/com.mypackage.myapp.x E/AndroidRuntime: at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:826)
Caused by: java.lang.RuntimeException: java.lang.ClassNotFoundException: com.mypackage.myapp.fragments.MainFragment
at androidx.navigation.fragment.b$a.a(Unknown Source:58)
at androidx.navigation.fragment.b$a.a(Unknown Source:19)
at androidx.navigation.j.a(Unknown Source:16)
at androidx.navigation.j.a(Unknown Source:133)
at androidx.navigation.j.a(Unknown Source:31)
... 38 more
Caused by: java.lang.ClassNotFoundException: com.mypackage.myapp.fragments.MainFragment
at java.lang.Class.classForName(Native Method)
at java.lang.Class.forName(Class.java:453)
at androidx.navigation.fragment.b$a.a(Unknown Source:45)
... 42 more
Caused by: java.lang.ClassNotFoundException: Didn't find class "com.mypackage.myapp.fragments.MainFragment" on path: DexPathList[[zip file "/system/framework/org.apache.http.legacy.boot.jar", zip file "/data/app/com.mypackage.myapp.x-ysts055HQTtJTv5J2uej3g==/base.apk"],nativeLibraryDirectories=[/data/app/com.mypackage.myapp.x-ysts055HQTtJTv5J2uej3g==/lib/x86, /system/lib]]
at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:125)
at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
... 45 more
It might be because AAPT is not yet producing keep rules for the navigation component?
I know that Proguard and R8 should be keeping all the children of library classes but in this case, the fragment class seems to be missing. This keep rule solved my issue but technically we should not need this rule at all!
-keep class * extends android.support.v4.app.Fragment{}
If you are using AndroidX, then use this rule: -keep class * extends androidx.fragment.app.Fragment{}
If you use argType in your navigation XML, you also need a rule for the referenced classes, for example: -keep class com.example.model.MyModel. Or even better, exclude parcelable and serializable classes from being renamed, as recommended by the official documentation.
-keepnames class * extends android.os.Parcelable
-keepnames class * extends java.io.Serializable