Fix fragment injection NPE

presentation/src/main/java/com/fernandocejas/android10/sample/presentation/view/fragment/BaseFragment.java

@@ -6,13 +6,42 @@
 package com.fernandocejas.android10.sample.presentation.view.fragment;
 
 import android.app.Fragment;
+import android.os.Bundle;
+import android.util.Log;
+import android.view.View;
 import android.widget.Toast;
 import com.fernandocejas.android10.sample.presentation.internal.di.HasComponent;
 
 /**
  * Base {@link android.app.Fragment} class for every fragment in this application.
  */
 public abstract class BaseFragment extends Fragment {
+
+  private boolean mIsInjected = false;
+
+  @Override public void onCreate(Bundle savedInstanceState) {
+    super.onCreate(savedInstanceState);
+    try {
+      mIsInjected = onInjectView();
+    } catch (IllegalStateException e) {
+      Log.e(e.getClass().getSimpleName(), e.getMessage());
+      mIsInjected = false;
+    }
+  }
+
+  @Override public void onViewCreated(View view, Bundle savedInstanceState) {
+    super.onViewCreated(view, savedInstanceState);
+    if (mIsInjected) onViewInjected(savedInstanceState);
+  }
+
+  @Override public void onActivityCreated(Bundle savedInstanceState) {
+    super.onActivityCreated(savedInstanceState);
+    if (!mIsInjected) {
+      mIsInjected = onInjectView();
+      if (mIsInjected) onViewInjected(null);
+    }
+  }
+
   /**
    * Shows a {@link android.widget.Toast} message.
    *
@@ -24,9 +53,46 @@ protected void showToastMessage(String message) {
 
   /**
    * Gets a component for dependency injection by its type.
+   *
+   * @throws IllegalStateException if component has not been initialized yet.
    */
   @SuppressWarnings("unchecked")
-  protected <C> C getComponent(Class<C> componentType) {
-    return componentType.cast(((HasComponent<C>) getActivity()).getComponent());
+  protected <C> C getComponent(Class<C> componentType) throws IllegalStateException {
+    C component = componentType.cast(((HasComponent<C>) getActivity()).getComponent());
+    if (component == null) {
+      throw new IllegalStateException(componentType.getSimpleName() + " has not been initialized yet.");
+    }
+    return component;
+  }
+
+  /**
+   * Called to do an optional injection. This will be called on {@link #onCreate(Bundle)} and if
+   * an exception is thrown or false returned, on {@link #onActivityCreated(Bundle)} again.
+   * Within this method get the injection component and inject the view. Based on returned value
+   * {@link #onViewInjected(Bundle)} will be called. Check {@link #onViewInjected(Bundle)}
+   * documentation for more info.
+   *
+   * @return True, if injection was successful, false otherwise. Returns false by default.
+   * @throws IllegalStateException If there is a failure in getting injection component or
+   *                               injection process itself. This can occur if activity holding
+   *                               component instance has been killed by the system and has not
+   *                               been initialized yet.
+   */
+  protected boolean onInjectView() throws IllegalStateException {
+    // Return false by default.
+    return false;
+  }
+
+  /**
+   * Called when the fragment has been injected and the field injected can be initialized. This
+   * will be called on {@link #onViewCreated(View, Bundle)} if {@link #onInjectView()} returned
+   * true when executed on {@link #onCreate(Bundle)}, otherwise it will be called on
+   * {@link #onActivityCreated(Bundle)} if {@link #onInjectView()} returned true right before.
+   *
+   * @param savedInstanceState If non-null, this fragment is being re-constructed
+   * from a previous saved state as given here.
+   */
+  protected void onViewInjected(Bundle savedInstanceState) {
+    // Intentionally left empty.
   }
 }

presentation/src/main/java/com/fernandocejas/android10/sample/presentation/view/fragment/UserDetailsFragment.java

@@ -43,20 +43,20 @@ public UserDetailsFragment() {
     setRetainInstance(true);
   }
 
-  @Override public void onCreate(Bundle savedInstanceState) {
-    super.onCreate(savedInstanceState);
+  @Override protected boolean onInjectView() throws IllegalStateException {
     this.getComponent(UserComponent.class).inject(this);
+    return true;
   }
 
   @Override public View onCreateView(LayoutInflater inflater, ViewGroup container,
-      Bundle savedInstanceState) {
+                                     Bundle savedInstanceState) {
     final View fragmentView = inflater.inflate(R.layout.fragment_user_details, container, false);
     ButterKnife.bind(this, fragmentView);
     return fragmentView;
   }
 
-  @Override public void onViewCreated(View view, Bundle savedInstanceState) {
-    super.onViewCreated(view, savedInstanceState);
+  @Override protected void onViewInjected(Bundle savedInstanceState) {
+    super.onViewInjected(savedInstanceState);
     this.userDetailsPresenter.setView(this);
     if (savedInstanceState == null) {
       this.loadUserDetails();

presentation/src/main/java/com/fernandocejas/android10/sample/presentation/view/fragment/UserListFragment.java

@@ -60,21 +60,21 @@ public UserListFragment() {
     }
   }
 
-  @Override public void onCreate(Bundle savedInstanceState) {
-    super.onCreate(savedInstanceState);
+  @Override protected boolean onInjectView() throws IllegalStateException {
     this.getComponent(UserComponent.class).inject(this);
+    return true;
   }
 
   @Override public View onCreateView(LayoutInflater inflater, ViewGroup container,
-      Bundle savedInstanceState) {
+                                     Bundle savedInstanceState) {
     final View fragmentView = inflater.inflate(R.layout.fragment_user_list, container, false);
     ButterKnife.bind(this, fragmentView);
-    setupRecyclerView();
     return fragmentView;
   }
 
-  @Override public void onViewCreated(View view, Bundle savedInstanceState) {
-    super.onViewCreated(view, savedInstanceState);
+  @Override protected void onViewInjected(Bundle savedInstanceState) {
+    super.onViewInjected(savedInstanceState);
+    this.setupRecyclerView();
     this.userListPresenter.setView(this);
     if (savedInstanceState == null) {
       this.loadUserList();