navigation/navigation-fragment/src/main/java/androidx/navigation/fragment/NavHostFragment.java - platform/frameworks/support - Git at Google

 /*
  * Copyright (C) 2017 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package androidx.navigation.fragment;

 import android.app.Dialog;
 import android.content.Context;
 import android.content.res.TypedArray;
 import android.os.Bundle;
 import android.util.AttributeSet;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;

 import androidx.activity.OnBackPressedDispatcher;
 import androidx.activity.OnBackPressedDispatcherOwner;
 import androidx.annotation.CallSuper;
 import androidx.annotation.NavigationRes;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.RestrictTo;
 import androidx.fragment.app.DialogFragment;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentContainerView;
 import androidx.navigation.NavController;
 import androidx.navigation.NavGraph;
 import androidx.navigation.NavHost;
 import androidx.navigation.NavHostController;
 import androidx.navigation.Navigation;
 import androidx.navigation.Navigator;

 /**
  * NavHostFragment provides an area within your layout for self-contained navigation to occur.
  *
  * <p>NavHostFragment is intended to be used as the content area within a layout resource
  * defining your app's chrome around it, e.g.:</p>
  *
  * <pre class="prettyprint">
  * &lt;androidx.drawerlayout.widget.DrawerLayout
  *        xmlns:android="http://schemas.android.com/apk/res/android"
  *        xmlns:app="http://schemas.android.com/apk/res-auto"
  *        android:layout_width="match_parent"
  *        android:layout_height="match_parent"&gt;
  *    &lt;fragment
  *            android:layout_width="match_parent"
  *            android:layout_height="match_parent"
  *            android:id="@+id/my_nav_host_fragment"
  *            android:name="androidx.navigation.fragment.NavHostFragment"
  *            app:navGraph="@navigation/nav_sample"
  *            app:defaultNavHost="true" /&gt;
  *    &lt;com.google.android.material.navigation.NavigationView
  *            android:layout_width="wrap_content"
  *            android:layout_height="match_parent"
  *            android:layout_gravity="start"/&gt;
  * &lt;/androidx.drawerlayout.widget.DrawerLayout&gt;
  * </pre>
  *
  * <p>Each NavHostFragment has a {@link NavController} that defines valid navigation within
  * the navigation host. This includes the {@link NavGraph navigation graph} as well as navigation
  * state such as current location and back stack that will be saved and restored along with the
  * NavHostFragment itself.</p>
  *
  * <p>NavHostFragments register their navigation controller at the root of their view subtree
  * such that any descendant can obtain the controller instance through the {@link Navigation}
  * helper class's methods such as {@link Navigation#findNavController(View)}. View event listener
  * implementations such as {@link android.view.View.OnClickListener} within navigation destination
  * fragments can use these helpers to navigate based on user interaction without creating a tight
  * coupling to the navigation host.</p>
  */
 public class NavHostFragment extends Fragment implements NavHost {
     /** @hide */
     @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
     protected static final String KEY_GRAPH_ID = "android-support-nav:fragment:graphId";
     /** @hide */
     @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
     protected static final String KEY_START_DESTINATION_ARGS =
             "android-support-nav:fragment:startDestinationArgs";
     private static final String KEY_NAV_CONTROLLER_STATE =
             "android-support-nav:fragment:navControllerState";
     private static final String KEY_DEFAULT_NAV_HOST = "android-support-nav:fragment:defaultHost";

     /**
      * Find a {@link NavController} given a local {@link Fragment}.
      *
      * <p>This method will locate the {@link NavController} associated with this Fragment,
      * looking first for a {@link NavHostFragment} along the given Fragment's parent chain.
      * If a {@link NavController} is not found, this method will look for one along this
      * Fragment's {@link Fragment#getView() view hierarchy} as specified by
      * {@link Navigation#findNavController(View)}.</p>
      *
      * @param fragment the locally scoped Fragment for navigation
      * @return the locally scoped {@link NavController} for navigating from this {@link Fragment}
      * @throws IllegalStateException if the given Fragment does not correspond with a
      * {@link NavHost} or is not within a NavHost.
      */
     @NonNull
     public static NavController findNavController(@NonNull Fragment fragment) {
         Fragment findFragment = fragment;
         while (findFragment != null) {
             if (findFragment instanceof NavHostFragment) {
                 return ((NavHostFragment) findFragment).getNavController();
             }
             Fragment primaryNavFragment = findFragment.getParentFragmentManager()
                     .getPrimaryNavigationFragment();
             if (primaryNavFragment instanceof NavHostFragment) {
                 return ((NavHostFragment) primaryNavFragment).getNavController();
             }
             findFragment = findFragment.getParentFragment();
         }

         // Try looking for one associated with the view instead, if applicable
         View view = fragment.getView();
         if (view != null) {
             return Navigation.findNavController(view);
         }

         // For DialogFragments, look at the dialog's decor view
         Dialog dialog = fragment instanceof DialogFragment
                 ? ((DialogFragment) fragment).getDialog()
                 : null;
         if (dialog != null && dialog.getWindow() != null) {
             return Navigation.findNavController(dialog.getWindow().getDecorView());
         }

         throw new IllegalStateException("Fragment " + fragment
                 + " does not have a NavController set");
     }

     private NavHostController mNavController;
     private Boolean mIsPrimaryBeforeOnCreate = null;
     private View mViewParent;

     // State that will be saved and restored
     private int mGraphId;
     private boolean mDefaultNavHost;

     /**
      * Create a new NavHostFragment instance with an inflated {@link NavGraph} resource.
      *
      * @param graphResId resource id of the navigation graph to inflate
      * @return a new NavHostFragment instance
      */
     @NonNull
     public static NavHostFragment create(@NavigationRes int graphResId) {
         return create(graphResId, null);
     }

     /**
      * Create a new NavHostFragment instance with an inflated {@link NavGraph} resource.
      *
      * @param graphResId Resource id of the navigation graph to inflate.
      * @param startDestinationArgs Arguments to send to the start destination of the graph.
      * @return A new NavHostFragment instance.
      */
     @NonNull
     public static NavHostFragment create(@NavigationRes int graphResId,
             @Nullable Bundle startDestinationArgs) {
         Bundle b = null;
         if (graphResId != 0) {
             b = new Bundle();
             b.putInt(KEY_GRAPH_ID, graphResId);
         }
         if (startDestinationArgs != null) {
             if (b == null) {
                 b = new Bundle();
             }
             b.putBundle(KEY_START_DESTINATION_ARGS, startDestinationArgs);
         }

         final NavHostFragment result = new NavHostFragment();
         if (b != null) {
             result.setArguments(b);
         }
         return result;
     }

     /**
      * Returns the {@link NavController navigation controller} for this navigation host.
      * This method will return null until this host fragment's {@link #onCreate(Bundle)}
      * has been called and it has had an opportunity to restore from a previous instance state.
      *
      * @return this host's navigation controller
      * @throws IllegalStateException if called before {@link #onCreate(Bundle)}
      */
     @NonNull
     @Override
     public final NavController getNavController() {
         if (mNavController == null) {
             throw new IllegalStateException("NavController is not available before onCreate()");
         }
         return mNavController;
     }

     @CallSuper
     @Override
     public void onAttach(@NonNull Context context) {
         super.onAttach(context);
         // TODO This feature should probably be a first-class feature of the Fragment system,
         // but it can stay here until we can add the necessary attr resources to
         // the fragment lib.
         if (mDefaultNavHost) {
             getParentFragmentManager().beginTransaction()
                     .setPrimaryNavigationFragment(this)
                     .commit();
         }
     }

     @CallSuper
     @Override
     public void onCreate(@Nullable Bundle savedInstanceState) {
         final Context context = requireContext();

         mNavController = new NavHostController(context);
         mNavController.setLifecycleOwner(this);
         if (context instanceof OnBackPressedDispatcherOwner) {
             mNavController.setOnBackPressedDispatcher(
                     ((OnBackPressedDispatcherOwner) context).getOnBackPressedDispatcher());
             // Otherwise, caller must register a dispatcher on the controller explicitly
             // by overriding onCreateNavHostController()
         }
         // Set the default state - this will be updated whenever
         // onPrimaryNavigationFragmentChanged() is called
         mNavController.enableOnBackPressed(
                 mIsPrimaryBeforeOnCreate != null && mIsPrimaryBeforeOnCreate);
         mIsPrimaryBeforeOnCreate = null;
         mNavController.setViewModelStore(getViewModelStore());
         onCreateNavHostController(mNavController);

         Bundle navState = null;
         if (savedInstanceState != null) {
             navState = savedInstanceState.getBundle(KEY_NAV_CONTROLLER_STATE);
             if (savedInstanceState.getBoolean(KEY_DEFAULT_NAV_HOST, false)) {
                 mDefaultNavHost = true;
                 getParentFragmentManager().beginTransaction()
                         .setPrimaryNavigationFragment(this)
                         .commit();
             }
             mGraphId = savedInstanceState.getInt(KEY_GRAPH_ID);
         }

         if (navState != null) {
             // Navigation controller state overrides arguments
             mNavController.restoreState(navState);
         }
         if (mGraphId != 0) {
             // Set from onInflate()
             mNavController.setGraph(mGraphId);
         } else {
             // See if it was set by NavHostFragment.create()
             final Bundle args = getArguments();
             final int graphId = args != null ? args.getInt(KEY_GRAPH_ID) : 0;
             final Bundle startDestinationArgs = args != null
                     ? args.getBundle(KEY_START_DESTINATION_ARGS)
                     : null;
             if (graphId != 0) {
                 mNavController.setGraph(graphId, startDestinationArgs);
             }
         }

         // We purposefully run this last as this will trigger the onCreate() of
         // child fragments, which may be relying on having the NavController already
         // created and having its state restored by that point.
         super.onCreate(savedInstanceState);
     }

     /**
      * Callback for when the {@link NavHostController} is created. If you
      * support any custom destination types, their {@link Navigator} should be added here to
      * ensure it is available before the navigation graph is inflated / set.
      * <p>
      * This provides direct access to the host specific methods available on
      * {@link NavHostController} such as
      * {@link NavHostController#setOnBackPressedDispatcher(OnBackPressedDispatcher)}.
      * <p>
      * By default, this adds a {@link DialogFragmentNavigator} and {@link FragmentNavigator}.
      * <p>
      * This is only called once in {@link #onCreate(Bundle)} and should not be called directly by
      * subclasses.
      *
      * @param navHostController The newly created {@link NavHostController} that will be
      *                          returned by {@link #getNavController()} after
      */
     @SuppressWarnings("deprecation")
     @CallSuper
     protected void onCreateNavHostController(@NonNull NavHostController navHostController) {
         onCreateNavController(navHostController);
     }

     /**
      * Callback for when the {@link #getNavController() NavController} is created. If you
      * support any custom destination types, their {@link Navigator} should be added here to
      * ensure it is available before the navigation graph is inflated / set.
      * <p>
      * By default, this adds a {@link DialogFragmentNavigator} and {@link FragmentNavigator}.
      * <p>
      * This is only called once in {@link #onCreate(Bundle)} and should not be called directly by
      * subclasses.
      *
      * @param navController The newly created {@link NavController}.
      * @deprecated Override {@link #onCreateNavHostController(NavHostController)} to gain
      * access to the full {@link NavHostController} that is created by this NavHostFragment.
      */
     @SuppressWarnings({"DeprecatedIsStillUsed", "deprecation"})
     @Deprecated
     @CallSuper
     protected void onCreateNavController(@NonNull NavController navController) {
         navController.getNavigatorProvider().addNavigator(
                 new DialogFragmentNavigator(requireContext(), getChildFragmentManager()));
         navController.getNavigatorProvider().addNavigator(createFragmentNavigator());
     }

     // TODO: DialogFragmentNavigator should use FragmentOnAttachListener from Fragment 1.3
     @SuppressWarnings("deprecation")
     @Override
     public void onAttachFragment(@NonNull Fragment childFragment) {
         super.onAttachFragment(childFragment);
         DialogFragmentNavigator dialogFragmentNavigator =
                 mNavController.getNavigatorProvider().getNavigator(DialogFragmentNavigator.class);
         dialogFragmentNavigator.onAttachFragment(childFragment);
     }

     @CallSuper
     @Override
     public void onPrimaryNavigationFragmentChanged(boolean isPrimaryNavigationFragment) {
         if (mNavController != null) {
             mNavController.enableOnBackPressed(isPrimaryNavigationFragment);
         } else {
             mIsPrimaryBeforeOnCreate = isPrimaryNavigationFragment;
         }
     }

     /**
      * Create the FragmentNavigator that this NavHostFragment will use. By default, this uses
      * {@link FragmentNavigator}, which replaces the entire contents of the NavHostFragment.
      * <p>
      * This is only called once in {@link #onCreate(Bundle)} and should not be called directly by
      * subclasses.
      * @return a new instance of a FragmentNavigator
      * @deprecated Use {@link #onCreateNavController(NavController)}
      */
     @Deprecated
     @NonNull
     protected Navigator<? extends FragmentNavigator.Destination> createFragmentNavigator() {
         return new FragmentNavigator(requireContext(), getChildFragmentManager(),
                 getContainerId());
     }

     @Nullable
     @Override
     public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                              @Nullable Bundle savedInstanceState) {
         FragmentContainerView containerView = new FragmentContainerView(inflater.getContext());
         // When added via XML, this has no effect (since this FragmentContainerView is given the ID
         // automatically), but this ensures that the View exists as part of this Fragment's View
         // hierarchy in cases where the NavHostFragment is added programmatically as is required
         // for child fragment transactions
         containerView.setId(getContainerId());
         return containerView;
     }

     /**
      * We specifically can't use {@link View#NO_ID} as the container ID (as we use
      * {@link androidx.fragment.app.FragmentTransaction#add(int, Fragment)} under the hood),
      * so we need to make sure we return a valid ID when asked for the container ID.
      *
      * @return a valid ID to be used to contain child fragments
      */
     private int getContainerId() {
         int id = getId();
         if (id != 0 && id != View.NO_ID) {
             return id;
         }
         // Fallback to using our own ID if this Fragment wasn't added via
         // add(containerViewId, Fragment)
         return R.id.nav_host_fragment_container;
     }

     @Override
     public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
         super.onViewCreated(view, savedInstanceState);
         if (!(view instanceof ViewGroup)) {
             throw new IllegalStateException("created host view " + view + " is not a ViewGroup");
         }
         Navigation.setViewNavController(view, mNavController);
         // When added programmatically, we need to set the NavController on the parent - i.e.,
         // the View that has the ID matching this NavHostFragment.
         if (view.getParent() != null) {
             mViewParent = (View) view.getParent();
             if (mViewParent.getId() == getId()) {
                 Navigation.setViewNavController(mViewParent, mNavController);
             }
         }
     }

     @CallSuper
     @Override
     public void onInflate(@NonNull Context context, @NonNull AttributeSet attrs,
             @Nullable Bundle savedInstanceState) {
         super.onInflate(context, attrs, savedInstanceState);

         final TypedArray navHost = context.obtainStyledAttributes(attrs,
                 androidx.navigation.R.styleable.NavHost);
         final int graphId = navHost.getResourceId(
                 androidx.navigation.R.styleable.NavHost_navGraph, 0);
         if (graphId != 0) {
             mGraphId = graphId;
         }
         navHost.recycle();

         final TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.NavHostFragment);
         final boolean defaultHost = a.getBoolean(R.styleable.NavHostFragment_defaultNavHost, false);
         if (defaultHost) {
             mDefaultNavHost = true;
         }
         a.recycle();
     }

     @CallSuper
     @Override
     public void onSaveInstanceState(@NonNull Bundle outState) {
         super.onSaveInstanceState(outState);
         Bundle navState = mNavController.saveState();
         if (navState != null) {
             outState.putBundle(KEY_NAV_CONTROLLER_STATE, navState);
         }
         if (mDefaultNavHost) {
             outState.putBoolean(KEY_DEFAULT_NAV_HOST, true);
         }
         if (mGraphId != 0) {
             outState.putInt(KEY_GRAPH_ID, mGraphId);
         }
     }

     @Override
     public void onDestroyView() {
         super.onDestroyView();
         if (mViewParent != null && Navigation.findNavController(mViewParent) == mNavController) {
             Navigation.setViewNavController(mViewParent, null);
         }
         mViewParent = null;
     }
 }
	/*
	* Copyright (C) 2017 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package androidx.navigation.fragment;

	import android.app.Dialog;
	import android.content.Context;
	import android.content.res.TypedArray;
	import android.os.Bundle;
	import android.util.AttributeSet;
	import android.view.LayoutInflater;
	import android.view.View;
	import android.view.ViewGroup;

	import androidx.activity.OnBackPressedDispatcher;
	import androidx.activity.OnBackPressedDispatcherOwner;
	import androidx.annotation.CallSuper;
	import androidx.annotation.NavigationRes;
	import androidx.annotation.NonNull;
	import androidx.annotation.Nullable;
	import androidx.annotation.RestrictTo;
	import androidx.fragment.app.DialogFragment;
	import androidx.fragment.app.Fragment;
	import androidx.fragment.app.FragmentContainerView;
	import androidx.navigation.NavController;
	import androidx.navigation.NavGraph;
	import androidx.navigation.NavHost;
	import androidx.navigation.NavHostController;
	import androidx.navigation.Navigation;
	import androidx.navigation.Navigator;

	/**
	* NavHostFragment provides an area within your layout for self-contained navigation to occur.
	*
	* <p>NavHostFragment is intended to be used as the content area within a layout resource
	* defining your app's chrome around it, e.g.:</p>
	*
	* <pre class="prettyprint">
	* <androidx.drawerlayout.widget.DrawerLayout
	* xmlns:android="http://schemas.android.com/apk/res/android"
	* xmlns:app="http://schemas.android.com/apk/res-auto"
	* android:layout_width="match_parent"
	* android:layout_height="match_parent">
	* <fragment
	* android:layout_width="match_parent"
	* android:layout_height="match_parent"
	* android:id="@+id/my_nav_host_fragment"
	* android:name="androidx.navigation.fragment.NavHostFragment"
	* app:navGraph="@navigation/nav_sample"
	* app:defaultNavHost="true" />
	* <com.google.android.material.navigation.NavigationView
	* android:layout_width="wrap_content"
	* android:layout_height="match_parent"
	* android:layout_gravity="start"/>
	* </androidx.drawerlayout.widget.DrawerLayout>
	* </pre>
	*
	* <p>Each NavHostFragment has a {@link NavController} that defines valid navigation within
	* the navigation host. This includes the {@link NavGraph navigation graph} as well as navigation
	* state such as current location and back stack that will be saved and restored along with the
	* NavHostFragment itself.</p>
	*
	* <p>NavHostFragments register their navigation controller at the root of their view subtree
	* such that any descendant can obtain the controller instance through the {@link Navigation}
	* helper class's methods such as {@link Navigation#findNavController(View)}. View event listener
	* implementations such as {@link android.view.View.OnClickListener} within navigation destination
	* fragments can use these helpers to navigate based on user interaction without creating a tight
	* coupling to the navigation host.</p>
	*/
	public class NavHostFragment extends Fragment implements NavHost {
	/** @hide */
	@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
	protected static final String KEY_GRAPH_ID = "android-support-nav:fragment:graphId";
	/** @hide */
	@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
	protected static final String KEY_START_DESTINATION_ARGS =
	"android-support-nav:fragment:startDestinationArgs";
	private static final String KEY_NAV_CONTROLLER_STATE =
	"android-support-nav:fragment:navControllerState";
	private static final String KEY_DEFAULT_NAV_HOST = "android-support-nav:fragment:defaultHost";

	/**
	* Find a {@link NavController} given a local {@link Fragment}.
	*
	* <p>This method will locate the {@link NavController} associated with this Fragment,
	* looking first for a {@link NavHostFragment} along the given Fragment's parent chain.
	* If a {@link NavController} is not found, this method will look for one along this
	* Fragment's {@link Fragment#getView() view hierarchy} as specified by
	* {@link Navigation#findNavController(View)}.</p>
	*
	* @param fragment the locally scoped Fragment for navigation
	* @return the locally scoped {@link NavController} for navigating from this {@link Fragment}
	* @throws IllegalStateException if the given Fragment does not correspond with a
	* {@link NavHost} or is not within a NavHost.
	*/
	@NonNull
	public static NavController findNavController(@NonNull Fragment fragment) {
	Fragment findFragment = fragment;
	while (findFragment != null) {
	if (findFragment instanceof NavHostFragment) {
	return ((NavHostFragment) findFragment).getNavController();
	}
	Fragment primaryNavFragment = findFragment.getParentFragmentManager()
	.getPrimaryNavigationFragment();
	if (primaryNavFragment instanceof NavHostFragment) {
	return ((NavHostFragment) primaryNavFragment).getNavController();
	}
	findFragment = findFragment.getParentFragment();
	}

	// Try looking for one associated with the view instead, if applicable
	View view = fragment.getView();
	if (view != null) {
	return Navigation.findNavController(view);
	}

	// For DialogFragments, look at the dialog's decor view
	Dialog dialog = fragment instanceof DialogFragment
	? ((DialogFragment) fragment).getDialog()
	: null;
	if (dialog != null && dialog.getWindow() != null) {
	return Navigation.findNavController(dialog.getWindow().getDecorView());
	}

	throw new IllegalStateException("Fragment " + fragment
	+ " does not have a NavController set");
	}

	private NavHostController mNavController;
	private Boolean mIsPrimaryBeforeOnCreate = null;
	private View mViewParent;

	// State that will be saved and restored
	private int mGraphId;
	private boolean mDefaultNavHost;

	/**
	* Create a new NavHostFragment instance with an inflated {@link NavGraph} resource.
	*
	* @param graphResId resource id of the navigation graph to inflate
	* @return a new NavHostFragment instance
	*/
	@NonNull
	public static NavHostFragment create(@NavigationRes int graphResId) {
	return create(graphResId, null);
	}

	/**
	* Create a new NavHostFragment instance with an inflated {@link NavGraph} resource.
	*
	* @param graphResId Resource id of the navigation graph to inflate.
	* @param startDestinationArgs Arguments to send to the start destination of the graph.
	* @return A new NavHostFragment instance.
	*/
	@NonNull
	public static NavHostFragment create(@NavigationRes int graphResId,
	@Nullable Bundle startDestinationArgs) {
	Bundle b = null;
	if (graphResId != 0) {
	b = new Bundle();
	b.putInt(KEY_GRAPH_ID, graphResId);
	}
	if (startDestinationArgs != null) {
	if (b == null) {
	b = new Bundle();
	}
	b.putBundle(KEY_START_DESTINATION_ARGS, startDestinationArgs);
	}

	final NavHostFragment result = new NavHostFragment();
	if (b != null) {
	result.setArguments(b);
	}
	return result;
	}

	/**
	* Returns the {@link NavController navigation controller} for this navigation host.
	* This method will return null until this host fragment's {@link #onCreate(Bundle)}
	* has been called and it has had an opportunity to restore from a previous instance state.
	*
	* @return this host's navigation controller
	* @throws IllegalStateException if called before {@link #onCreate(Bundle)}
	*/
	@NonNull
	@Override
	public final NavController getNavController() {
	if (mNavController == null) {
	throw new IllegalStateException("NavController is not available before onCreate()");
	}
	return mNavController;
	}

	@CallSuper
	@Override
	public void onAttach(@NonNull Context context) {
	super.onAttach(context);
	// TODO This feature should probably be a first-class feature of the Fragment system,
	// but it can stay here until we can add the necessary attr resources to
	// the fragment lib.
	if (mDefaultNavHost) {
	getParentFragmentManager().beginTransaction()
	.setPrimaryNavigationFragment(this)
	.commit();
	}
	}

	@CallSuper
	@Override
	public void onCreate(@Nullable Bundle savedInstanceState) {
	final Context context = requireContext();

	mNavController = new NavHostController(context);
	mNavController.setLifecycleOwner(this);
	if (context instanceof OnBackPressedDispatcherOwner) {
	mNavController.setOnBackPressedDispatcher(
	((OnBackPressedDispatcherOwner) context).getOnBackPressedDispatcher());
	// Otherwise, caller must register a dispatcher on the controller explicitly
	// by overriding onCreateNavHostController()
	}
	// Set the default state - this will be updated whenever
	// onPrimaryNavigationFragmentChanged() is called
	mNavController.enableOnBackPressed(
	mIsPrimaryBeforeOnCreate != null && mIsPrimaryBeforeOnCreate);
	mIsPrimaryBeforeOnCreate = null;
	mNavController.setViewModelStore(getViewModelStore());
	onCreateNavHostController(mNavController);

	Bundle navState = null;
	if (savedInstanceState != null) {
	navState = savedInstanceState.getBundle(KEY_NAV_CONTROLLER_STATE);
	if (savedInstanceState.getBoolean(KEY_DEFAULT_NAV_HOST, false)) {
	mDefaultNavHost = true;
	getParentFragmentManager().beginTransaction()
	.setPrimaryNavigationFragment(this)
	.commit();
	}
	mGraphId = savedInstanceState.getInt(KEY_GRAPH_ID);
	}

	if (navState != null) {
	// Navigation controller state overrides arguments
	mNavController.restoreState(navState);
	}
	if (mGraphId != 0) {
	// Set from onInflate()
	mNavController.setGraph(mGraphId);
	} else {
	// See if it was set by NavHostFragment.create()
	final Bundle args = getArguments();
	final int graphId = args != null ? args.getInt(KEY_GRAPH_ID) : 0;
	final Bundle startDestinationArgs = args != null
	? args.getBundle(KEY_START_DESTINATION_ARGS)
	: null;
	if (graphId != 0) {
	mNavController.setGraph(graphId, startDestinationArgs);
	}
	}

	// We purposefully run this last as this will trigger the onCreate() of
	// child fragments, which may be relying on having the NavController already
	// created and having its state restored by that point.
	super.onCreate(savedInstanceState);
	}

	/**
	* Callback for when the {@link NavHostController} is created. If you
	* support any custom destination types, their {@link Navigator} should be added here to
	* ensure it is available before the navigation graph is inflated / set.
	* <p>
	* This provides direct access to the host specific methods available on
	* {@link NavHostController} such as
	* {@link NavHostController#setOnBackPressedDispatcher(OnBackPressedDispatcher)}.
	* <p>
	* By default, this adds a {@link DialogFragmentNavigator} and {@link FragmentNavigator}.
	* <p>
	* This is only called once in {@link #onCreate(Bundle)} and should not be called directly by
	* subclasses.
	*
	* @param navHostController The newly created {@link NavHostController} that will be
	* returned by {@link #getNavController()} after
	*/
	@SuppressWarnings("deprecation")
	@CallSuper
	protected void onCreateNavHostController(@NonNull NavHostController navHostController) {
	onCreateNavController(navHostController);
	}

	/**
	* Callback for when the {@link #getNavController() NavController} is created. If you
	* support any custom destination types, their {@link Navigator} should be added here to
	* ensure it is available before the navigation graph is inflated / set.
	* <p>
	* By default, this adds a {@link DialogFragmentNavigator} and {@link FragmentNavigator}.
	* <p>
	* This is only called once in {@link #onCreate(Bundle)} and should not be called directly by
	* subclasses.
	*
	* @param navController The newly created {@link NavController}.
	* @deprecated Override {@link #onCreateNavHostController(NavHostController)} to gain
	* access to the full {@link NavHostController} that is created by this NavHostFragment.
	*/
	@SuppressWarnings({"DeprecatedIsStillUsed", "deprecation"})
	@Deprecated
	@CallSuper
	protected void onCreateNavController(@NonNull NavController navController) {
	navController.getNavigatorProvider().addNavigator(
	new DialogFragmentNavigator(requireContext(), getChildFragmentManager()));
	navController.getNavigatorProvider().addNavigator(createFragmentNavigator());
	}

	// TODO: DialogFragmentNavigator should use FragmentOnAttachListener from Fragment 1.3
	@SuppressWarnings("deprecation")
	@Override
	public void onAttachFragment(@NonNull Fragment childFragment) {
	super.onAttachFragment(childFragment);
	DialogFragmentNavigator dialogFragmentNavigator =
	mNavController.getNavigatorProvider().getNavigator(DialogFragmentNavigator.class);
	dialogFragmentNavigator.onAttachFragment(childFragment);
	}

	@CallSuper
	@Override
	public void onPrimaryNavigationFragmentChanged(boolean isPrimaryNavigationFragment) {
	if (mNavController != null) {
	mNavController.enableOnBackPressed(isPrimaryNavigationFragment);
	} else {
	mIsPrimaryBeforeOnCreate = isPrimaryNavigationFragment;
	}
	}

	/**
	* Create the FragmentNavigator that this NavHostFragment will use. By default, this uses
	* {@link FragmentNavigator}, which replaces the entire contents of the NavHostFragment.
	* <p>
	* This is only called once in {@link #onCreate(Bundle)} and should not be called directly by
	* subclasses.
	* @return a new instance of a FragmentNavigator
	* @deprecated Use {@link #onCreateNavController(NavController)}
	*/
	@Deprecated
	@NonNull
	protected Navigator<? extends FragmentNavigator.Destination> createFragmentNavigator() {
	return new FragmentNavigator(requireContext(), getChildFragmentManager(),
	getContainerId());
	}

	@Nullable
	@Override
	public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
	@Nullable Bundle savedInstanceState) {
	FragmentContainerView containerView = new FragmentContainerView(inflater.getContext());
	// When added via XML, this has no effect (since this FragmentContainerView is given the ID
	// automatically), but this ensures that the View exists as part of this Fragment's View
	// hierarchy in cases where the NavHostFragment is added programmatically as is required
	// for child fragment transactions
	containerView.setId(getContainerId());
	return containerView;
	}

	/**
	* We specifically can't use {@link View#NO_ID} as the container ID (as we use
	* {@link androidx.fragment.app.FragmentTransaction#add(int, Fragment)} under the hood),
	* so we need to make sure we return a valid ID when asked for the container ID.
	*
	* @return a valid ID to be used to contain child fragments
	*/
	private int getContainerId() {
	int id = getId();
	if (id != 0 && id != View.NO_ID) {
	return id;
	}
	// Fallback to using our own ID if this Fragment wasn't added via
	// add(containerViewId, Fragment)
	return R.id.nav_host_fragment_container;
	}

	@Override
	public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
	super.onViewCreated(view, savedInstanceState);
	if (!(view instanceof ViewGroup)) {
	throw new IllegalStateException("created host view " + view + " is not a ViewGroup");
	}
	Navigation.setViewNavController(view, mNavController);
	// When added programmatically, we need to set the NavController on the parent - i.e.,
	// the View that has the ID matching this NavHostFragment.
	if (view.getParent() != null) {
	mViewParent = (View) view.getParent();
	if (mViewParent.getId() == getId()) {
	Navigation.setViewNavController(mViewParent, mNavController);
	}
	}
	}

	@CallSuper
	@Override
	public void onInflate(@NonNull Context context, @NonNull AttributeSet attrs,
	@Nullable Bundle savedInstanceState) {
	super.onInflate(context, attrs, savedInstanceState);

	final TypedArray navHost = context.obtainStyledAttributes(attrs,
	androidx.navigation.R.styleable.NavHost);
	final int graphId = navHost.getResourceId(
	androidx.navigation.R.styleable.NavHost_navGraph, 0);
	if (graphId != 0) {
	mGraphId = graphId;
	}
	navHost.recycle();

	final TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.NavHostFragment);
	final boolean defaultHost = a.getBoolean(R.styleable.NavHostFragment_defaultNavHost, false);
	if (defaultHost) {
	mDefaultNavHost = true;
	}
	a.recycle();
	}

	@CallSuper
	@Override
	public void onSaveInstanceState(@NonNull Bundle outState) {
	super.onSaveInstanceState(outState);
	Bundle navState = mNavController.saveState();
	if (navState != null) {
	outState.putBundle(KEY_NAV_CONTROLLER_STATE, navState);
	}
	if (mDefaultNavHost) {
	outState.putBoolean(KEY_DEFAULT_NAV_HOST, true);
	}
	if (mGraphId != 0) {
	outState.putInt(KEY_GRAPH_ID, mGraphId);
	}
	}

	@Override
	public void onDestroyView() {
	super.onDestroyView();
	if (mViewParent != null && Navigation.findNavController(mViewParent) == mNavController) {
	Navigation.setViewNavController(mViewParent, null);
	}
	mViewParent = null;
	}
	}