Fix view state persistence

flow-sample/src/main/java/com/example/flow/MainActivity.java

@@ -64,16 +64,13 @@ protected void onCreate(Bundle savedInstanceState) {
     GsonParceler parceler = new GsonParceler(new Gson());
     @SuppressWarnings("deprecation") ActivityFlowSupport.NonConfigurationInstance nonConfig =
         (ActivityFlowSupport.NonConfigurationInstance) getLastNonConfigurationInstance();
-    flowSupport = ActivityFlowSupport.onCreate(nonConfig, getIntent(), savedInstanceState, parceler,
-        Backstack.single(new Paths.ConversationList()));
-
     final ActionBar actionBar = getActionBar();
     actionBar.setDisplayShowHomeEnabled(false);
-
     setContentView(R.layout.root_layout);
-
     container = (PathContainerView) findViewById(R.id.container);
     containerAsBackTarget = (HandlesBack) container;
+    flowSupport = ActivityFlowSupport.onCreate(nonConfig, getIntent(), savedInstanceState, parceler,
+        Backstack.single(new Paths.ConversationList()), this);
   }
 
   @Override protected void onNewIntent(Intent intent) {
@@ -83,7 +80,7 @@ protected void onCreate(Bundle savedInstanceState) {
 
   @Override protected void onResume() {
     super.onResume();
-    flowSupport.onResume(this);
+    flowSupport.onResume();
   }
 
   @Override protected void onPause() {

flow-sample/src/main/java/com/example/flow/view/FriendView.java

@@ -18,7 +18,7 @@
 
 import android.content.Context;
 import android.util.AttributeSet;
-import android.widget.FrameLayout;
+import android.widget.LinearLayout;
 import android.widget.TextView;
 import butterknife.ButterKnife;
 import butterknife.InjectView;
@@ -30,7 +30,7 @@
 import java.util.List;
 import javax.inject.Inject;
 
-public class FriendView extends FrameLayout {
+public class FriendView extends LinearLayout {
   @Inject List<User> friends;
 
   private final User friend;

flow-sample/src/main/res/layout/friend_view.xml

@@ -20,11 +20,19 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
+    android:orientation="vertical"
     android:id="@+id/friend_view"
     >
   <TextView
       android:id="@+id/friend_info"
       android:layout_width="match_parent"
-      android:layout_height="match_parent"
+      android:layout_height="wrap_content"
+      />
+  <EditText
+      android:id="@+id/friend_note"
+      android:freezesText="true"
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content"
+      android:minLines="2"
       />
 </com.example.flow.view.FriendView>

flow/src/main/java/flow/ActivityFlowSupport.java

@@ -2,10 +2,9 @@
 
 import android.content.Intent;
 import android.os.Bundle;
-import java.util.Iterator;
+import android.os.Parcelable;
 
 import static flow.Preconditions.checkArgument;
-import static flow.Preconditions.checkState;
 
 /**
  * Manages a Flow within an Activity.  Make sure that each method is called from the corresponding
@@ -79,14 +78,18 @@ public static void setBackstackExtra(Intent intent, Backstack backstack, Parcele
   private final Parceler parceler;
   private final Flow flow;
   private Flow.Dispatcher dispatcher;
+  private boolean dispatcherSet;
 
-  private ActivityFlowSupport(Flow flow, Parceler parceler) {
+  private ActivityFlowSupport(Flow flow, Flow.Dispatcher dispatcher, Parceler parceler) {
     this.flow = flow;
+    this.dispatcher = dispatcher;
     this.parceler = parceler;
   }
 
+  /** Immediately starts the Dispatcher, so the dispatcher should be prepared before calling. */
   public static ActivityFlowSupport onCreate(NonConfigurationInstance nonConfigurationInstance,
-      Intent intent, Bundle savedInstanceState, Parceler parceler, Backstack defaultBackstack) {
+      Intent intent, Bundle savedInstanceState, Parceler parceler, Backstack defaultBackstack,
+      Flow.Dispatcher dispatcher) {
     checkArgument(parceler != null, "parceler may not be null");
     final Flow flow;
     if (nonConfigurationInstance != null) {
@@ -98,7 +101,8 @@ public static ActivityFlowSupport onCreate(NonConfigurationInstance nonConfigura
       }
       flow = new Flow(selectBackstack(intent, savedBackstack, defaultBackstack, parceler));
     }
-    return new ActivityFlowSupport(flow, parceler);
+    flow.setDispatcher(dispatcher);
+    return new ActivityFlowSupport(flow, dispatcher, parceler);
   }
 
   public void onNewIntent(Intent intent) {
@@ -109,21 +113,20 @@ public void onNewIntent(Intent intent) {
     }
   }
 
-  public void onResume(Flow.Dispatcher dispatcher) {
-    checkArgument(dispatcher != null, "dispatcher may not be null");
-    this.dispatcher = dispatcher;
-
-    flow.setDispatcher(dispatcher);
+  public void onResume() {
+    if (!dispatcherSet) {
+      dispatcherSet = true;
+      flow.setDispatcher(dispatcher);
+    }
   }
 
   public NonConfigurationInstance onRetainNonConfigurationInstance() {
     return new NonConfigurationInstance(flow);
   }
 
   public void onPause() {
-    checkState(dispatcher != null, "Did you forget to call onResume()?");
     flow.removeDispatcher(dispatcher);
-    dispatcher = null;
+    dispatcherSet = false;
   }
 
   /**
@@ -135,10 +138,15 @@ public boolean onBackPressed() {
 
   public void onSaveInstanceState(Bundle outState) {
     checkArgument(outState != null, "outState may not be null");
-    Backstack backstack = getBackstackToSave(flow.getBackstack());
-    if (backstack == null) return;
-    //noinspection ConstantConditions
-    outState.putParcelable(BACKSTACK_KEY, backstack.getParcelable(parceler));
+    Parcelable parcelable = flow.getBackstack().getParcelable(parceler, new Backstack.Filter() {
+      @Override public boolean apply(Object state) {
+        return !state.getClass().isAnnotationPresent(NotPersistent.class);
+      }
+    });
+    if (parcelable != null) {
+      //noinspection ConstantConditions
+      outState.putParcelable(BACKSTACK_KEY, parcelable);
+    }
   }
 
   /**
@@ -161,18 +169,4 @@ private static Backstack selectBackstack(Intent intent, Backstack saved,
     }
     return defaultBackstack;
   }
-
-  private static Backstack getBackstackToSave(Backstack backstack) {
-    Iterator<Object> it = backstack.reverseIterator();
-    Backstack.Builder save = Backstack.emptyBuilder();
-    boolean empty = true;
-    while (it.hasNext()) {
-      Object state = it.next();
-      if (!state.getClass().isAnnotationPresent(NotPersistent.class)) {
-        save.push(state);
-        empty = false;
-      }
-    }
-    return empty ? null : save.build();
-  }
 }

flow/src/main/java/flow/Backstack.java

@@ -31,7 +31,9 @@
  * Describes the history of a {@link Flow} at a specific point in time.
  */
 public final class Backstack implements Iterable<Object> {
-  private final Deque<Entry> backstack;
+  public static interface Filter {
+    boolean apply(Object state);
+  }
 
   /** Restore a saved backstack from a {@link Parcelable} using the supplied {@link Parceler}. */
   public static Backstack from(Parcelable parcelable, Parceler parceler) {
@@ -47,18 +49,38 @@ public static Backstack from(Parcelable parcelable, Parceler parceler) {
     return new Backstack(entries);
   }
 
+  private final Deque<Entry> backstack;
+
   /** Get a {@link Parcelable} of this backstack using the supplied {@link Parceler}. */
   public Parcelable getParcelable(Parceler parceler) {
     Bundle backstackBundle = new Bundle();
-
     ArrayList<Bundle> entryBundles = new ArrayList<>(backstack.size());
-
     for (Entry entry : backstack) {
-      Bundle entryBundle = new Bundle();
-      entryBundle.putParcelable("OBJECT", parceler.wrap(entry.state));
-      entryBundle.putSparseParcelableArray("VIEW_STATE", entry.viewState);
-      entryBundles.add(entryBundle);
+     entryBundles.add(entry.getBundle(parceler));
+    }
+    backstackBundle.putParcelableArrayList("ENTRIES", entryBundles);
+    return backstackBundle;
+  }
+
+  /**
+   * Get a {@link Parcelable} of this backstack using the supplied {@link Parceler}, filtered
+   * by the supplied {@link Filter}.
+   *
+   * The filter is invoked on each state in the stack in reverse order
+   *
+   * @return null if all states are filtered out.
+   */
+  public Parcelable getParcelable(Parceler parceler, Filter filter) {
+    Bundle backstackBundle = new Bundle();
+    ArrayList<Bundle> entryBundles = new ArrayList<>(backstack.size());
+    Iterator<Entry> it = backstack.descendingIterator();
+    while (it.hasNext()) {
+      Entry entry = it.next();
+      if (filter.apply(entry.state)) {
+        entryBundles.add(entry.getBundle(parceler));
+      }
     }
+    Collections.reverse(entryBundles);
     backstackBundle.putParcelableArrayList("ENTRIES", entryBundles);
     return backstackBundle;
   }
@@ -128,6 +150,13 @@ private static final class Entry implements ViewState {
       }
     }
 
+    Bundle getBundle(Parceler parceler) {
+      Bundle bundle = new Bundle();
+      bundle.putParcelable("OBJECT", parceler.wrap(state));
+      bundle.putSparseParcelableArray("VIEW_STATE", viewState);
+      return bundle;
+    }
+
     @Override
     public boolean equals(Object o) {
       if (this == o) return true;