Add predictive back gesture support to MainActivity.

app/src/main/AndroidManifest.xml

@@ -101,6 +101,7 @@
                  android:supportsRtl="true"
                  android:resizeableActivity="true"
                  android:fullBackupOnly="false"
+                 android:enableOnBackInvokedCallback="false"
                  android:allowBackup="true"
                  android:backupAgent=".absbackup.SignalBackupAgent"
                  android:theme="@style/TextSecure.LightTheme"
@@ -1069,6 +1070,7 @@
               android:exported="false"/>
 
     <activity android:name=".MainActivity"
+              android:enableOnBackInvokedCallback="true"
               android:theme="@style/Theme.Signal.DayNight.NoActionBar"
               android:configChanges="touchscreen|keyboard|keyboardHidden|orientation|screenLayout|screenSize"
               android:resizeableActivity="true"

app/src/main/java/org/thoughtcrime/securesms/MainActivity.kt

@@ -260,12 +260,6 @@ class MainActivity : PassphraseRequiredActivity(), VoiceNoteMediaControllerOwner
     SplashScreenUtil.setSplashScreenThemeIfNecessary(this, SignalStore.settings.theme)
   }
 
-  override fun onBackPressed() {
-    if (!navigator.onBackPressed()) {
-      super.onBackPressed()
-    }
-  }
-
   override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
     super.onActivityResult(requestCode, resultCode, data)
     if (requestCode == MainNavigator.REQUEST_CONFIG_CHANGES && resultCode == RESULT_CONFIG_CHANGED) {

app/src/main/java/org/thoughtcrime/securesms/MainNavigator.java

@@ -6,10 +6,8 @@ import android.content.Intent;
 import androidx.annotation.MainThread;
 import androidx.annotation.NonNull;
 import androidx.appcompat.app.AppCompatActivity;
-import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentManager;
 import androidx.lifecycle.ViewModelProvider;
-import androidx.lifecycle.viewmodel.internal.ViewModelProviders;
 
 import org.signal.core.util.concurrent.LifecycleDisposable;
 import org.thoughtcrime.securesms.components.settings.app.AppSettingsActivity;
@@ -54,20 +52,6 @@ public class MainNavigator {
     return ((NavigatorProvider) activity).getNavigator();
   }
 
-  /**
-   * @return True if the back pressed was handled in our own custom way, false if it should be given
-   * to the system to do the default behavior.
-   */
-  public boolean onBackPressed() {
-    Fragment fragment = getFragmentManager().findFragmentById(R.id.fragment_container);
-
-    if (fragment instanceof BackHandler) {
-      return ((BackHandler) fragment).onBackPressed();
-    }
-
-    return false;
-  }
-
   public void goToConversation(@NonNull RecipientId recipientId, long threadId, int distributionType, int startingPosition) {
     Disposable disposable = ConversationIntents.createBuilder(activity, recipientId, threadId)
                                                .map(builder -> builder.withDistributionType(distributionType)

app/src/main/java/org/thoughtcrime/securesms/conversationlist/ConversationListFragment.java

@@ -244,6 +244,7 @@ public class ConversationListFragment extends MainFragment implements ActionMode
   private   ConversationListTabsViewModel         conversationListTabsViewModel;
   private   ContactSearchMediator                 contactSearchMediator;
   private   MainToolbarViewModel                  mainToolbarViewModel;
+  private   ChatListBackHandler                   chatListBackHandler;
 
   private BannerManager bannerManager;
 
@@ -428,16 +429,8 @@ public class ConversationListFragment extends MainFragment implements ActionMode
 
     RatingManager.showRatingDialogIfNecessary(requireContext());
 
-    requireActivity().getOnBackPressedDispatcher().addCallback(getViewLifecycleOwner(), new OnBackPressedCallback(true) {
-      @Override
-      public void handleOnBackPressed() {
-        if (!closeSearchIfOpen()) {
-          if (!NavHostFragment.findNavController(ConversationListFragment.this).popBackStack()) {
-            requireActivity().finish();
-          }
-        }
-      }
-    });
+    chatListBackHandler = new ChatListBackHandler(false);
+    requireActivity().getOnBackPressedDispatcher().addCallback(getViewLifecycleOwner(), chatListBackHandler);
 
     conversationListTabsViewModel = new ViewModelProvider(requireActivity()).get(ConversationListTabsViewModel.class);
 
@@ -658,15 +651,14 @@ public class ConversationListFragment extends MainFragment implements ActionMode
     return mainToolbarViewModel.getState().getValue().getMode() == MainToolbarMode.SEARCH;
   }
 
-  private boolean closeSearchIfOpen() {
+  private void closeSearchIfOpen() {
     if (isSearchOpen()) {
       setAdapter(defaultAdapter);
       fadeInButtonsAndMegaphone(250);
       mainToolbarViewModel.setToolbarMode(MainToolbarMode.FULL);
+      chatListBackHandler.setEnabled(false);
       return true;
     }
-
-    return false;
   }
 
   @Override
@@ -1690,6 +1682,7 @@ public class ConversationListFragment extends MainFragment implements ActionMode
   }
 
   private void onSearchOpen() {
+    chatListBackHandler.setEnabled(true);
     fadeOutButtonsAndMegaphone(250);
   }
 
@@ -1697,6 +1690,8 @@ public class ConversationListFragment extends MainFragment implements ActionMode
     if (list != null) {
       setAdapter(defaultAdapter);
     }
+
+    chatListBackHandler.setEnabled(false);
     fadeInButtonsAndMegaphone(250);
   }
 
@@ -1970,6 +1965,18 @@ public class ConversationListFragment extends MainFragment implements ActionMode
     }
   }
 
+  private class ChatListBackHandler extends OnBackPressedCallback {
+
+    public ChatListBackHandler(boolean enabled) {
+      super(enabled);
+    }
+
+    @Override
+    public void handleOnBackPressed() {
+      closeSearchIfOpen();
+    }
+  }
+
   public interface Callback extends Material3OnScrollHelperBinder {
     void updateProxyStatus(@NonNull WebSocketConnectionState state);