title: ClassNotFoundException: Didn't find class "android.support.v4.content.FileProvider" after androidx migration
body: <p>I'm trying to move to migrate to androidx. I used the migration tool in Android Studio. When I do this I get the following stacktrace when I run my app.</p>
  
  <pre><code>E/AndroidRuntime: FATAL EXCEPTION: main
      Process: com.peerke.outdoorpuzzlegame.debug, PID: 10901
      java.lang.RuntimeException: Unable to get provider android.support.v4.content.FileProvider: java.lang.ClassNotFoundException: Didn't find class "android.support.v4.content.FileProvider" on path: DexPathList[[zip file "/data/app/com.peerke.outdoorpuzzlegame.debug-IBtFsngoLqc-cQb_hOO5wQ==/base.apk"],nativeLibraryDirectories=[/data/app/com.peerke.outdoorpuzzlegame.debug-IBtFsngoLqc-cQb_hOO5wQ==/lib/x86, /system/lib]]
          at android.app.ActivityThread.installProvider(ActivityThread.java:6376)
          at android.app.ActivityThread.installContentProviders(ActivityThread.java:5932)
          at android.app.ActivityThread.handleBindApplication(ActivityThread.java:5847)
          at android.app.ActivityThread.access$1000(ActivityThread.java:198)
          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1637)
          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: java.lang.ClassNotFoundException: Didn't find class "android.support.v4.content.FileProvider" on path: DexPathList[[zip file "/data/app/com.peerke.outdoorpuzzlegame.debug-IBtFsngoLqc-cQb_hOO5wQ==/base.apk"],nativeLibraryDirectories=[/data/app/com.peerke.outdoorpuzzlegame.debug-IBtFsngoLqc-cQb_hOO5wQ==/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)
          at android.app.AppComponentFactory.instantiateProvider(AppComponentFactory.java:121)
          at androidx.core.app.CoreComponentFactory.instantiateProvider(CoreComponentFactory.java:62)
          at android.app.ActivityThread.installProvider(ActivityThread.java:6360)
          at android.app.ActivityThread.installContentProviders(ActivityThread.java:5932) 
          at android.app.ActivityThread.handleBindApplication(ActivityThread.java:5847) 
          at android.app.ActivityThread.access$1000(ActivityThread.java:198) 
          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1637) 
          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) 
  </code></pre>
  
  <p>The exception is correct. android.support.v4.content.FileProvider doesn't exist in my app. But androidx.core.content.FileProvider is included in my app. 
  The big question is why does it want to load the old version of FileProvider? </p>