Avoid nullable filesDir

app/src/main/java/org/solovyev/android/calculator/AppModule.java

@@ -7,6 +7,7 @@ import android.os.Handler;
 import android.os.Looper;
 import android.preference.PreferenceManager;
 import android.support.annotation.NonNull;
+import android.util.Log;
 import com.squareup.otto.Bus;
 import com.squareup.otto.GeneratedHandlerFinder;
 import dagger.Module;
@@ -19,6 +20,7 @@ import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import javax.inject.Named;
 import javax.inject.Singleton;
+import java.io.File;
 import java.util.Collections;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Executors;
@@ -34,6 +36,7 @@ public class AppModule {
     public static final String THREAD_UI = "thread-ui";
     // multiple threads
     public static final String THREAD_BACKGROUND = "thread-background";
+    public static final String DIR_FILES = "dir-files";
 
     @NonNull
     private final Application application;
@@ -146,6 +149,31 @@ public class AppModule {
         return Typeface.createFromAsset(application.getAssets(), "fonts/Roboto-Regular.ttf");
     }
 
+    @Singleton
+    @Provides
+    @Named(DIR_FILES)
+    File provideFilesDir(@Named(THREAD_INIT) Executor initThread) {
+        final File filesDir = makeFilesDir();
+        initThread.execute(new Runnable() {
+            @Override
+            public void run() {
+                if (!filesDir.exists() && !filesDir.mkdirs()) {
+                    Log.e(App.TAG, "Can't create files dirs");
+                }
+            }
+        });
+        return filesDir;
+    }
+
+    @Nonnull
+    private File makeFilesDir() {
+        final File filesDir = application.getFilesDir();
+        if (filesDir == null) {
+            return new File(application.getApplicationInfo().dataDir, "files");
+        }
+        return filesDir;
+    }
+
     private static class AppBus extends Bus {
 
         @NonNull

app/src/main/java/org/solovyev/android/calculator/VariablesRegistry.java

@@ -129,7 +129,7 @@ public class VariablesRegistry extends BaseEntitiesRegistry<IConstant> {
     @Override
     @NonNull
     protected File getEntitiesFile() {
-        return new File(application.getFilesDir(), "variables.json");
+        return new File(filesDir, "variables.json");
     }
 
     @Nullable

app/src/main/java/org/solovyev/android/calculator/entities/BaseEntitiesRegistry.java

@@ -75,6 +75,9 @@ public abstract class BaseEntitiesRegistry<T extends MathEntity> implements Enti
     @Inject
     @Named(AppModule.THREAD_BACKGROUND)
     public Executor backgroundThread;
+    @Inject
+    @Named(AppModule.DIR_FILES)
+    public File filesDir;
 
     // synchronized on lock
     private boolean initialized;

app/src/main/java/org/solovyev/android/calculator/functions/FunctionsRegistry.java

@@ -134,7 +134,7 @@ public class FunctionsRegistry extends BaseEntitiesRegistry<Function> {
     @Override
     @NonNull
     protected File getEntitiesFile() {
-        return new File(application.getFilesDir(), "functions.json");
+        return new File(filesDir, "functions.json");
     }
 
     @Nonnull

app/src/main/java/org/solovyev/android/calculator/history/History.java

@@ -86,6 +86,9 @@ public class History {
     @Inject
     @Named(AppModule.THREAD_BACKGROUND)
     Executor backgroundThread;
+    @Inject
+    @Named(AppModule.DIR_FILES)
+    File filesDir;
 
     @Nullable
     static List<HistoryState> convertOldHistory(@NonNull String xml) {
@@ -170,12 +173,12 @@ public class History {
 
     @NonNull
     private File getSavedHistoryFile() {
-        return new File(application.getFilesDir(), "history-saved.json");
+        return new File(filesDir, "history-saved.json");
     }
 
     @NonNull
     private File getRecentHistoryFile() {
-        return new File(application.getFilesDir(), "history-recent.json");
+        return new File(filesDir, "history-recent.json");
     }
 
     private void migrateOldHistory() {