1. Basic use
Import library
def nav_version = "2.3.2"
// Java language implementation
implementation "androidx.navigation:navigation-fragment:$nav_version"
implementation "androidx.navigation:navigation-ui:$nav_version"
Copy the codeThe Activity layout
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<! App :defaultNavHost="true" -->
<androidx.fragment.app.FragmentContainerView
android:id="@+id/my_nav_host_fragment"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="9"
android:name="androidx.navigation.fragment.NavHostFragment"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:defaultNavHost="true"
app:navGraph="@navigation/nav_graph_main"/>
</LinearLayout>
Copy the codeNav_graph_main.xml in the res/navigation directory
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/nav_graph_main.xml"
app:startDestination="@id/page1Fragment">
<fragment
android:id="@+id/page1Fragment"
android:name="com.example.lsn4_navigationdemo.MainPage1Fragment"
android:label="fragment_page1"
tools:layout="@layout/fragment_main_page1">
<! --action: jump to destination class with id -->
<action
android:id="@+id/action_page2"
app:destination="@id/page2Fragment" />
</fragment>
<fragment
android:id="@+id/page2Fragment"
android:name="com.example.lsn4_navigationdemo.MainPage2Fragment"
android:label="fragment_page2"
tools:layout="@layout/fragment_main_page2">
<action
android:id="@+id/action_page1"
app:destination="@id/page1Fragment" />
<action
android:id="@+id/action_page3"
app:destination="@id/page3Fragment" />
</fragment>
<! -- <navigation-->
<! -- android:id="@+id/nav_graph_page3"-->
<! -- app:startDestination="@id/page3Fragment">-->
<fragment
android:id="@+id/page3Fragment"
android:name="com.example.lsn4_navigationdemo.MainPage3Fragment"
android:label="fragment_page3"
tools:layout="@layout/fragment_main_page3"
>
<action
android:id="@+id/action_page2"
app:destination="@id/page2Fragment"/>
</fragment>
</navigation>
Copy the codeFragment calls a jump
// Method 1: Jump to the specified fragment
Navigation.findNavController(view).navigate(R.id.page2Fragment);
// Mode 2: Action
Navigation.findNavController(view).navigate(R.id.action_page2); / / jump into page2
Copy the codeInvoke a jump in the Activity
// Obtain controller in method 1
NavController controller=Navigation.findNavController(this,R.id.my_nav_host_fragment);
// Obtain controller in method 2
NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.my_nav_host_fragment);
NavController controller = navHostFragment.getNavController();
/ / jump
controller.navigate(R.id.page2Fragment);
Copy the codeThe Activity binding navigation
In addition to specifying navigation layout resources in the Activity’s layout, you can also set them through Java code
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/ / way
val finalHost = NavHostFragment.create(R.navigation.nav_graph_main)
supportFragmentManager.beginTransaction()
.replace(R.id.ll_fragment_navigation, finalHost)
.setPrimaryNavigationFragment(finalHost)
.commit();
}
2 / / way
@Override
public boolean onSupportNavigateUp(a) {
Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.my_nav_host_fragment);
returnNavHostFragment.findNavController(fragment).navigateUp(); }}Copy the codeAt the bottom of the navigation
Introduces the bottom navigation control
implementation 'com. Google. Android. Material: material: 1.1.0'
Copy the codelayout
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<! App :defaultNavHost="true" -->
<androidx.fragment.app.FragmentContainerView
android:id="@+id/my_nav_host_fragment"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="9"
android:name="androidx.navigation.fragment.NavHostFragment"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:defaultNavHost="true"
app:navGraph="@navigation/nav_graph_main"/>
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/nav_view"
android:layout_width="match_parent"
android:layout_weight="1"
android:layout_height="wrap_content"
app:itemTextColor="#ff0000"
app:menu="@menu/menu"/>
</LinearLayout>
Copy the codemenu
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@+id/page1Fragment"
android:icon="@drawable/ic_launcher_foreground"
android:title="1"/>
<item
android:id="@+id/page2Fragment"
android:icon="@drawable/ic_launcher_foreground"
android:title="2"/>
<item
android:id="@+id/page3Fragment"
android:icon="@drawable/ic_launcher_foreground"
android:title="3"/>
</menu>
Copy the codeActivity binding navigation
public class MainActivity extends AppCompatActivity {
BottomNavigationView bottomNavigationView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.action_page1);
bottomNavigationView=findViewById(R.id.nav_view);
// Obtain controller in method 1
//NavController controller=Navigation.findNavController(this,R.id.my_nav_host_fragment);
// Obtain controller in method 2
NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.my_nav_host_fragment);
NavController controller = navHostFragment.getNavController();
// Bind navigation
NavigationUI.setupWithNavController(bottomNavigationView,controller);
}
Copy the codePrinciple 2.
Initialize the NavHostFragment life cycle method
1. The create – NavHostFragment created
In NavHostFragment. The create method
- Initialize the Bundle and store graphResId, startDestinationArgs in the Bundle.
- New NavHostFragment() returns the NavHostFragment instance.
//NavHostFragment.java
@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;
}
Copy the code2. OnInflate — parsing of the XML file
The main thing is to resolve the two properties of the layout file, defaultNavHost and navGraph, and initialize the global variables.
NavHostFragment. OnInflate method when fragments, in the form of XML static load, the first is called onInflate method (called time: fragments of the associated Activity when performing the setContentView).
//NavHostFragment.java
@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; // Navigation map layout
}
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; // Whether to listen for the physical return key
}
a.recycle();
}
Copy the code3. OnCreateNavController – create the Navigator
When implementing navigation, we need to generate NavGraph class according to navigation configuration file, and then according to each different actionID, find the corresponding NavDestination to realize the page navigation jump.
Create the Navigator
The Navigator class instantiates the corresponding NavDestination, implements navigation, and has its own fallback stack.
@CallSuper
protected void onCreateNavController(@NonNull NavController navController) {
navController.getNavigatorProvider().addNavigator(
new DialogFragmentNavigator(requireContext(), getChildFragmentManager()));
// Create a Navigator and bind it to NavigatorProvider.
//mNavigatorProvider is a global variable in NavController that internally holds the Navigator class in the form of HashMap key-value pairs.
navController.getNavigatorProvider().addNavigator(createFragmentNavigator());
}
Copy the code- MNavigatorProvider is the global variable in NavController, which internally saves the Navigator class in the form of HashMap key-value pairs
- The createFragmentNavigator method builds the FragmentNavigator object, which contains the abstract class Navigator and the important implementation classes ActivityNavigator and NavGraphNavigator. This two-class object is added to the Constructor of the NavController.
//NavController.java
public NavController(@NonNull Context context) {
mContext = context;
while (context instanceof ContextWrapper) {
if (context instanceof Activity) {
mActivity = (Activity) context;
break;
}
context = ((ContextWrapper) context).getBaseContext();
}
mNavigatorProvider.addNavigator(new NavGraphNavigator(mNavigatorProvider));
mNavigatorProvider.addNavigator(new ActivityNavigator(mContext));
}
Copy the code4. OnCreate – Navigation initialization
Either the XML implementation or the code implementation executes the Fragment’s onCreate method. The NavController is created here and there is a NavController object in the NavHostFragment.
@CallSuper
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
final Context context = requireContext();
//1. Initialize NavController. NavController is the core class
mNavController = new NavHostController(context);
mNavController.setLifecycleOwner(this); mNavController.setOnBackPressedDispatcher(requireActivity().getOnBackPressedDispatcher()); mNavController.enableOnBackPressed( mIsPrimaryBeforeOnCreate ! =null && mIsPrimaryBeforeOnCreate);
mIsPrimaryBeforeOnCreate = null;
mNavController.setViewModelStore(getViewModelStore());
onCreateNavController(mNavController);
Bundle navState = null;
//2. The system starts to recover
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) {
mNavController.restoreState(navState);
}
//3. Set the navigation chart information
if(mGraphId ! =0) {
mNavController.setGraph(mGraphId);
} else {
final Bundle args = getArguments();
final intgraphId = args ! =null ? args.getInt(KEY_GRAPH_ID) : 0;
finalBundle startDestinationArgs = args ! =null
? args.getBundle(KEY_START_DESTINATION_ARGS)
: null;
if(graphId ! =0) { mNavController.setGraph(graphId, startDestinationArgs); }}super.onCreate(savedInstanceState);
}
Copy the code5.onCreateView
The NavHostFragment view has only one FragmentContainerView that inherits FrameLayout
//NavHostFragment.java
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
@Nullable Bundle savedInstanceState) {
FragmentContainerView containerView = new FragmentContainerView(inflater.getContext());
// This line is mainly used to add fragments in code
containerView.setId(getContainerId());
return containerView;
}
Copy the code6.onViewCreated
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
if(! (viewinstanceof ViewGroup)) {
throw new IllegalStateException("created host view " + view + " is not a ViewGroup");
}
// Add the mNavController to the view tag
Navigation.setViewNavController(view, mNavController);
if(view.getParent() ! =null) {
mViewParent = (View) view.getParent();
if (mViewParent.getId() == getId()) {
// Add the mNavController to the view tagNavigation.setViewNavController(mViewParent, mNavController); }}}Copy the codeGet NavController
1. Obtain NavController
NavHostFragment.findNavController(fragment)
Copy the code //NavHostFragment.java
@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();
}
View view = fragment.getView();
if(view ! =null) {
return Navigation.findNavController(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");
}
Copy the code2. FindNavController in Navigation
3.findViewNavController
View. Tag to find NavController. The getViewNavController method is called internally.
4.getViewNavController
The getViewNavController method retrieves the NavController object by retrieving the view’s Tag, where the Tag ID and setViewNavController are both nav_controller_view_tag.
//Navigation.java
@NonNull
public static NavController findNavController(@NonNull View view) {
/ / 3.
NavController navController = findViewNavController(view);
if (navController == null) {
throw new IllegalStateException("View " + view + " does not have a NavController set");
}
return navController;
}
@Nullable
private static NavController findViewNavController(@NonNull View view) {
while(view ! =null) {
NavController controller = getViewNavController(view);
if(controller ! =null) {
return controller;
}
ViewParent parent = view.getParent();
view = parent instanceof View ? (View) parent : null;
}
return null;
}
@Nullable
private static NavController getViewNavController(@NonNull View view) {
//4. The tag ID and setViewNavController are both nav_controller_view_tag.
Object tag = view.getTag(R.id.nav_controller_view_tag);
NavController controller = null;
if (tag instanceof WeakReference) {
controller = ((WeakReference<NavController>) tag).get();
} else if (tag instanceof NavController) {
controller = (NavController) tag;
}
return controller;
}
Copy the codeNavigation navigate
navigate
After building and getting the NavController object and the NavGraph. Here’s how to use it for real navigation. Begin the analysis with navigate. NavDestination is queried inside the Navigate method and navigated according to the different Navigator implementation.
public void navigate(@IdRes int resId, @Nullable Bundle args, @Nullable NavOptions navOptions,
@Nullable Navigator.Extras navigatorExtras) {
NavDestination currentNode = mBackStack.isEmpty()
? mGraph
: mBackStack.getLast().getDestination();
if (currentNode == null) {
throw new IllegalStateException("no current navigation node");
}
@IdRes int destId = resId;
//2. Obtain the corresponding NavAction based on the ID
final NavAction navAction = currentNode.getAction(resId);
Bundle combinedArgs = null;
if(navAction ! =null) {
if (navOptions == null) {
navOptions = navAction.getNavOptions();
}
//3. Use NavAction to obtain the destination ID
destId = navAction.getDestinationId();
Bundle navActionArgs = navAction.getDefaultArguments();
if(navActionArgs ! =null) {
combinedArgs = newBundle(); combinedArgs.putAll(navActionArgs); }}if(args ! =null) {
if (combinedArgs == null) {
combinedArgs = new Bundle();
}
combinedArgs.putAll(args);
}
if (destId == 0&& navOptions ! =null&& navOptions.getPopUpTo() ! = -1) {
popBackStack(navOptions.getPopUpTo(), navOptions.isPopUpToInclusive());
return;
}
if (destId == 0) {
throw new IllegalArgumentException("Destination id == 0 can only be used"
+ " in conjunction with a valid navOptions.popUpTo");
}
//4. Use the destination ID attribute to find the destination to navigate to using the findDestination method
NavDestination node = findDestination(destId);
if (node == null) {
final String dest = NavDestination.getDisplayName(mContext, destId);
if(navAction ! =null) {
throw new IllegalArgumentException("Navigation destination " + dest
+ " referenced from action "
+ NavDestination.getDisplayName(mContext, resId)
+ " cannot be found from the current destination " + currentNode);
} else {
throw new IllegalArgumentException("Navigation action/destination " + dest
+ " cannot be found from the current destination "+ currentNode); }}//5. Start navigation
navigate(node, combinedArgs, navOptions, navigatorExtras);
}
private void navigate(@NonNull NavDestination node, @Nullable Bundle args,
@Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {
boolean popped = false;
boolean launchSingleTop = false;
if(navOptions ! =null) {
if(navOptions.getPopUpTo() ! = -1) { popped = popBackStackInternal(navOptions.getPopUpTo(), navOptions.isPopUpToInclusive()); } } Navigator<NavDestination> navigator = mNavigatorProvider.getNavigator( node.getNavigatorName()); Bundle finalArgs = node.addInDefaultArgs(args); NavDestination newDest = navigator.navigate(node, finalArgs, navOptions, navigatorExtras); . }Copy the codefindDestination
NavGraph is returned if the rollback stack is NULL, and the last item in the rollback stack is not returned if null.
NavDestination findDestination(@IdRes int destinationId) {
if (mGraph == null) {
return null;
}
if (mGraph.getId() == destinationId) {
return mGraph;
}
//1. If the rollback is null, return NavGraph. If the rollback is not null, return the last item in the rollback.
NavDestination currentNode = mBackStack.isEmpty()
? mGraph
: mBackStack.getLast().getDestination();
NavGraph currentGraph = currentNode instanceof NavGraph
? (NavGraph) currentNode
: currentNode.getParent();
return currentGraph.findNode(destinationId);
}
Copy the codeThe realization of the FragmentNavigator
The above analysis brings us to the FragmentNavigator subclass. Take a look at FragmentNavigator. Navigate method. (1) call instantiateFragment to build Fragment instances via reflection mechanism (2) handle animation logic such as inbound and outbound (3) Finally call FragmentManager to handle navigation logic.
@Nullable
@Override
public NavDestination navigate(@NonNull Destination destination, @Nullable Bundle args,
@Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {
if (mFragmentManager.isStateSaved()) {
Log.i(TAG, "Ignoring navigate() call: FragmentManager has already"
+ " saved its state");
return null;
}
String className = destination.getClassName();
if (className.charAt(0) = ='. ') {
className = mContext.getPackageName() + className;
}
// Build a Fragment instance using reflection
final Fragment frag = instantiateFragment(mContext, mFragmentManager,
className, args);
frag.setArguments(args);
final FragmentTransaction ft = mFragmentManager.beginTransaction();
// Handle animation logic
intenterAnim = navOptions ! =null ? navOptions.getEnterAnim() : -1;
intexitAnim = navOptions ! =null ? navOptions.getExitAnim() : -1;
intpopEnterAnim = navOptions ! =null ? navOptions.getPopEnterAnim() : -1;
intpopExitAnim = navOptions ! =null ? navOptions.getPopExitAnim() : -1;
if(enterAnim ! = -1|| exitAnim ! = -1|| popEnterAnim ! = -1|| popExitAnim ! = -1) { enterAnim = enterAnim ! = -1 ? enterAnim : 0; exitAnim = exitAnim ! = -1 ? exitAnim : 0; popEnterAnim = popEnterAnim ! = -1 ? popEnterAnim : 0; popExitAnim = popExitAnim ! = -1 ? popExitAnim : 0;
ft.setCustomAnimations(enterAnim, exitAnim, popEnterAnim, popExitAnim);
}
//FragmentManager to handle navigation logic
ft.replace(mContainerId, frag);
ft.setPrimaryNavigationFragment(frag);
final @IdRes int destId = destination.getId();
final boolean initialNavigation = mBackStack.isEmpty();
final booleanisSingleTopReplacement = navOptions ! =null && !initialNavigation
&& navOptions.shouldLaunchSingleTop()
&& mBackStack.peekLast() == destId;
boolean isAdded;
if (initialNavigation) {
isAdded = true;
} else if (isSingleTopReplacement) {
if (mBackStack.size() > 1) {
mFragmentManager.popBackStack(
generateBackStackName(mBackStack.size(), mBackStack.peekLast()),
FragmentManager.POP_BACK_STACK_INCLUSIVE);
ft.addToBackStack(generateBackStackName(mBackStack.size(), destId));
}
isAdded = false;
} else {
ft.addToBackStack(generateBackStackName(mBackStack.size() + 1, destId));
isAdded = true;
}
if (navigatorExtras instanceof Extras) {
Extras extras = (Extras) navigatorExtras;
for (Map.Entry<View, String> sharedElement : extras.getSharedElements().entrySet()) {
ft.addSharedElement(sharedElement.getKey(), sharedElement.getValue());
}
}
ft.setReorderingAllowed(true);
ft.commit();
if (isAdded) {
mBackStack.add(destId);
return destination;
} else {
return null; }}Copy the codeActivityNavigator
ActivityNavigator eventually calls the startActivity method as well. Read the source code for yourself.
@Nullable
@Override
public NavDestination navigate(@NonNull Destination destination, @Nullable Bundle args,
@Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {...if (navigatorExtras instanceof Extras) {
Extras extras = (Extras) navigatorExtras;
ActivityOptionsCompat activityOptions = extras.getActivityOptions();
if(activityOptions ! =null) {
ActivityCompat.startActivity(mContext, intent, activityOptions.toBundle());
} else{ mContext.startActivity(intent); }}else{ mContext.startActivity(intent); }... }Copy the code3. Summary
- The NavHostFragment acts as a navigation carrier, is referenced in the Activity layout file (or dynamically in code), and holds a NavController reference to the navigation control class.
- The NavController delegates navigation to the Navigator class, which has two important subclasses FragmentNavigator and ActivityNavigator. The NavController class holds NavInflater class references.
- The NavInflater parses the Navnavigation file and builds the NavGraph.
- NavDestination holds Destination information, and there is a Destination class inside FragmentNavigator and ActivityNavigator that inherits NavDestination.
- During page navigation, FragmentManager handles fragment operations and startActivity handles activity.
