Custom AppComponentFactory Fails to Instantiate Application

Question

I am attempting to implement a custom AppComponentFactory to create my Application and Activity instances using non-zero arg constructors (Dagger based constructor dependency injection), but my app fails to launch because my custom Application subtype does not have a zero arg constructor, and the stack trace implies my custom AppComponentFactory is not being used.

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.domain.app, PID: 32670
    java.lang.RuntimeException: Unable to instantiate application com.domain.app.CustomApplication: java.lang.InstantiationException: java.lang.Class<com.domain.app.CustomApplication> has no zero argument constructor
        at android.app.LoadedApk.makeApplication(LoadedApk.java:1226)
        at android.app.ActivityThread.handleBindApplication(ActivityThread.java:6431)
        at android.app.ActivityThread.access$1300(ActivityThread.java:219)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1859)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.InstantiationException: java.lang.Class<com.domain.app.CustomApplication> has no zero argument constructor
        at java.lang.Class.newInstance(Native Method)
        at android.app.AppComponentFactory.instantiateApplication(AppComponentFactory.java:76)
        at android.app.Instrumentation.newApplication(Instrumentation.java:1155)
        at android.app.LoadedApk.makeApplication(LoadedApk.java:1218)
        at android.app.ActivityThread.handleBindApplication(ActivityThread.java:6431) 
        at android.app.ActivityThread.access$1300(ActivityThread.java:219) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1859) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 

UPDATE: Upon further examination, there was another error in Logcat showing that the system failed to find my custom AppComponentFactory.

E/LoadedApk: Unable to instantiate appComponentFactory
    java.lang.ClassNotFoundException: Didn't find class "com.domain.app.appname.CustomAppComponentFactory" on path: DexPathList[[zip file "/data/app/com.domain.app.appname-8VLkpKFTUtW8k-xEHX-oMQ==/base.apk"],nativeLibraryDirectories=[/data/app/com.domain.app.appname-8VLkpKFTUtW8k-xEHX-oMQ==/lib/arm64, /system/lib64, /system/product/lib64]]
        at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:196)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
        at android.app.LoadedApk.createAppFactory(LoadedApk.java:256)
        at android.app.LoadedApk.createOrUpdateClassLoaderLocked(LoadedApk.java:855)
        at android.app.LoadedApk.getClassLoader(LoadedApk.java:950)
        at android.app.LoadedApk.getResources(LoadedApk.java:1188)
        at android.app.ContextImpl.createAppContext(ContextImpl.java:2462)
        at android.app.ContextImpl.createAppContext(ContextImpl.java:2454)
        at android.app.ActivityThread.handleBindApplication(ActivityThread.java:6343)
        at android.app.ActivityThread.access$1300(ActivityThread.java:219)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1859)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

Answer 1

In my case this was caused by not using a fully qualified class name in the manifest. It appears that when you use the shorthand .ClassName syntax for the android:appComponentFactory attribute the system prepends the applicationId instead of the package declared in the manifest element. To get the system to recognize my CustomAppComponentFactory I had to change my manifest from this:

<application
    android:appComponentFactory=".CustomAppComponentFactory"
    ....
    >

to this:

<application
    android:appComponentFactory="com.domain.app.CustomAppComponentFactory"
    ....
    >

Note that I also had to add tools:replace="appComponentFactory" to the application element in the manifest to make all this work, but there was a clear error message about a manifest merger error with androidx.core.app.CoreComponentFactory that suggested adding the replace attribute.