介绍
官方学习文档
导航Navigator是方便用户在一个主Activity包含多个Fragment时，进行内容片断的切换的交互。
优点：
1）将处理Fragment的事务进行了封装处理，用户不需要再处理该类事务
2）切换的动画标准化了
3）只需要配置好导航视图即可方便切换
4）片断之间的数据传递需要使用Gradle插件（该点本文未涉及）
三个角色：
导航图：该图包含了导航需要的相关信息，全部保存在xml资源文件中
NavHost: 负责显示目标内容的容器；
NavController: 管理导航的对象，根据需要来替换显示容器中的内容；
Navigation使用
1、添加依赖
val nav_version = "2.3.5"
// Java language implementation
implementation("androidx.navigation:navigation-fragment:$nav_version")
implementation("androidx.navigation:navigation-ui:$nav_version")
2、创建导航图
在res/navigation/nav_graph.xml 这里的文件名会在布局文件中使用；
navigation 是导航图的根节点，
**app:startDestination 指定第一个目的地**fragment标签：指明了目的地的信息
**id 属性 是唯一标识，用于在代码中引用该目的地** **name 属性 目的地的全类名** **Label 属性 包含该目的地的用户可读名称** **tool:layout: 属性 指定对应的布局文件**action标签： 是目的地的子元素，例如有安装点击跳转时，可以直接调用action的对应的id即可
3、布局文件XML添加NavHostFragment容器
name: 是指定的NavHost的实现类
app:navGraph 指向导航视图文件，这样导航控制器根据这个导航视图就可以导航所有的目的地
app:defaultNavHost: 这个属性时确保NavHostFragment会拦截系统的返回事件。
4、初始化导航控制器
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_navigator_main);
NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.fragment_container);
//这里就可以得到导航控制器
NavController navController = navHostFragment.getNavController();
}
5、操作导航控制器
Button btn = view.findViewById(R.id.btn1);
btn.setOnClickListener(v -> {
//这里的v 是当前操作的view ,navigate中的参数就是我们的导航视图中写好的action 的Id
Navigation.findNavController(v).navigate(R.id.gotoSectond);
});
6、结合BottomNavigationView 使用
1）引入依赖包
implementation 'com.google.android.material:material:1.1.0'
2）创建Menu
3）添加布局
4）绑定NavController
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_navigator_main);
BottomNavigationView bottomNavigationView = findViewById(R.id.nav_view);
NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.fragment_container);
NavController navController = navHostFragment.getNavController();
//下面通过NavigationUI将bottomNavigationView 与 navController进行绑定
NavigationUI.setupWithNavController(bottomNavigationView, navController);
}
原理分析
当Activity 加载Fragment时，先从xml布局文件中解析导航视图的ID，当Fragment创建的时候根据解析出来的导航视图的ID找到导航视图的第一个目的地视图的ID ,然后找到对应该目的地ID的节点信息，通过类加载器加载找到的目的地ID对应的Fragment，最后通过FragmentSupportManager 来替换默认的显示容器，从而显示出来。
当在调用navigate导航新的目的地时，会根据传入的actionID ，找到新的目的地ID ,然后重复上面的步骤通过类加载器来加载新目的地Fragment ，然后再次替换显示容器。
以上就是Navigator的执行过程，其中核心的技术是：XMLPull解析，类加载 ，工厂模式来创建目的地实例
1、创建第一个目的地Fragment(从Fragment的生命周期分析)
navigator加载第一个目的地
1.1）NavHostFragment的onInflate（）解析布局文件
解析布局文件中的defaultNavHost 、navGraph 的值，并保存下来
@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();
}
1.2) NavHostFragment的onCreate
1.2.1)、 创建NavHostController 并添加FragmentNavigator
public void onCreate(@Nullable Bundle savedInstanceState) {
final Context context = requireContext();
// 创建NavHostController
mNavController = new NavHostController(context);
mNavController.setLifecycleOwner(this);
mNavController.setOnBackPressedDispatcher(requireActivity().getOnBackPressedDispatcher());
// Set the default state - this will be updated whenever
// onPrimaryNavigationFragmentChanged() is called
mNavController.enableOnBackPressed(
mIsPrimaryBeforeOnCreate != null && mIsPrimaryBeforeOnCreate);
mIsPrimaryBeforeOnCreate = null;
mNavController.setViewModelStore(getViewModelStore());
// 给NavHostController 的provider 添加FragmentNavigator
onCreateNavController(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()
//此处官方已经注释是在onInflate()中解析到布局文件中的值，这里是关键
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);
}
1.2.2) NavController 设置Graph
1)、inflate 导航视图
XMLPull 解析器解析导航视图xml文件
创建NavDestination(NavGraph)，
dest.onInflate(mContext, attrs); 这里需要注意，由于NavGraph 是NavDestination 的子类，所以这里会调入NavGraph 的onInflate()方法中
//NavInflater.java
@SuppressLint("ResourceType")
@NonNull
public NavGraph inflate(@NavigationRes int graphResId) {
Resources res = mContext.getResources();
XmlResourceParser parser = res.getXml(graphResId);
final AttributeSet attrs = Xml.asAttributeSet(parser);
try {
int type;
while ((type = parser.next()) != XmlPullParser.START_TAG
&& type != XmlPullParser.END_DOCUMENT) {
// Empty loop
}
if (type != XmlPullParser.START_TAG) {
throw new XmlPullParserException("No start tag found");
}
String rootElement = parser.getName();
//解析NavDestination
NavDestination destination = inflate(res, parser, attrs, graphResId);
if (!(destination instanceof NavGraph)) {
throw new IllegalArgumentException("Root element <" + rootElement + ">"
+ " did not inflate into a NavGraph");
}
return (NavGraph) destination;
} catch (Exception e) {
throw new RuntimeException("Exception inflating "
+ res.getResourceName(graphResId) + " line "
+ parser.getLineNumber(), e);
} finally {
parser.close();
}
}
@NonNull
private NavDestination inflate(@NonNull Resources res, @NonNull XmlResourceParser parser,
@NonNull AttributeSet attrs, int graphResId)
throws XmlPullParserException, IOException {
Navigator navigator = mNavigatorProvider.getNavigator(parser.getName());
//这里创建一个NavDestination
final NavDestination dest = navigator.createDestination();
//进入NavDestination 的onInflate中 这里需要特别注意
dest.onInflate(mContext, attrs);
final int innerDepth = parser.getDepth() + 1;
int type;
int depth;
while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& ((depth = parser.getDepth()) >= innerDepth
|| type != XmlPullParser.END_TAG)) {
if (type != XmlPullParser.START_TAG) {
continue;
}
if (depth > innerDepth) {
continue;
}
final String name = parser.getName();
if (TAG_ARGUMENT.equals(name)) {
inflateArgumentForDestination(res, dest, attrs, graphResId);
} else if (TAG_DEEP_LINK.equals(name)) {
inflateDeepLink(res, dest, attrs);
} else if (TAG_ACTION.equals(name)) {
inflateAction(res, dest, attrs, parser, graphResId);
} else if (TAG_INCLUDE.equals(name) && dest instanceof NavGraph) {
final TypedArray a = res.obtainAttributes(
attrs, androidx.navigation.R.styleable.NavInclude);
final int id = a.getResourceId(
androidx.navigation.R.styleable.NavInclude_graph, 0);
((NavGraph) dest).addDestination(inflate(id));
a.recycle();
} else if (dest instanceof NavGraph) {
((NavGraph) dest).addDestination(inflate(res, parser, attrs, graphResId));
}
}
return dest;
}
//NavGraph.java
@Override
public void onInflate(@NonNull Context context, @NonNull AttributeSet attrs) {
super.onInflate(context, attrs);//这句话又会调用NavDestination 的onInflate方法
TypedArray a = context.getResources().obtainAttributes(attrs,
R.styleable.NavGraphNavigator);
//下面就更导航视图文件的根节点解析到了第一个目的地
setStartDestination(
a.getResourceId(R.styleable.NavGraphNavigator_startDestination, 0));
mStartDestIdName = getDisplayName(context, mStartDestId);
a.recycle();
}
///NavDestination.java
public void onInflate(@NonNull Context context, @NonNull AttributeSet attrs) {
final TypedArray a = context.getResources().obtainAttributes(attrs,
R.styleable.Navigator);
setId(a.getResourceId(R.styleable.Navigator_android_id, 0));
mIdName = getDisplayName(context, mId);
setLabel(a.getText(R.styleable.Navigator_android_label));
a.recycle();
}
@Override
public void onInflate(@NonNull Context context, @NonNull AttributeSet attrs) {
super.onInflate(context, attrs);
TypedArray a = context.getResources().obtainAttributes(attrs,
R.styleable.NavGraphNavigator);
setStartDestination(
a.getResourceId(R.styleable.NavGraphNavigator_startDestination, 0));
mStartDestIdName = getDisplayName(context, mStartDestId);
a.recycle();
}
//NavGraph.java
2)、setGraph()
//NavController.java
public void setGraph(@NavigationRes int graphResId) {
setGraph(graphResId, null);
}
//>>>>>>>>>>>>>>>>>>>>>>>>>>>>
@CallSuper
public void setGraph(@NavigationRes int graphResId, @Nullable Bundle startDestinationArgs) {
//下面的startDestinationArgs 是通过上一步传递进来的null
//这里进入inflate，参数就是导航文件
setGraph(getNavInflater().inflate(graphResId), startDestinationArgs);
}
//>>>>>>>>>>>>>>>>>>>>>>>>>>>>
public void setGraph(@NonNull NavGraph graph, @Nullable Bundle startDestinationArgs) {
if (mGraph != null) {
// Pop everything from the old graph off the back stack
popBackStackInternal(mGraph.getId(), true);
}
mGraph = graph;//此处将创建的NavDestination保存下来
onGraphCreated(startDestinationArgs);
}
//>>>>>>>>>>>>>>>>>>>>>>>>>>>>
private void onGraphCreated(@Nullable Bundle startDestinationArgs) {
//此处省略了干扰代码
if (mGraph != null && mBackStack.isEmpty()) {
boolean deepLinked = !mDeepLinkHandled && mActivity != null
&& handleDeepLink(mActivity.getIntent());
if (!deepLinked) {
// Navigate to the first destination in the graph
// if we haven't deep linked to a destination
//这里将第一个目的地作为第一个参数传递进去
navigate(mGraph, startDestinationArgs, null, null);
}
} else {
dispatchOnDestinationChanged();
}
}
//>>>>>>>>>>>>>>>>>>>>>>>>>>>>
private void navigate(@NonNull NavDestination node, @Nullable Bundle args,
@Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {
//.........
Navigator navigator = mNavigatorProvider.getNavigator(
node.getNavigatorName());
Bundle finalArgs = node.addInDefaultArgs(args);
// 此处使用Navigator 进行导航，而Navigator是抽象类，那么就进入他的实现类FragmentNavigator
NavDestination newDest = navigator.navigate(node, finalArgs,
navOptions, navigatorExtras);
//.....
}
3)、FragmentNavigator 的Navigate()
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;
}
//这里会根据目的地创建一个Fragment
final Fragment frag = instantiateFragment(mContext, mFragmentManager,
className, args);
frag.setArguments(args);
//下面就开始Fragment transcation了
final FragmentTransaction ft = mFragmentManager.beginTransaction();
int enterAnim = navOptions != null ? navOptions.getEnterAnim() : -1;
int exitAnim = navOptions != null ? navOptions.getExitAnim() : -1;
int popEnterAnim = navOptions != null ? navOptions.getPopEnterAnim() : -1;
int popExitAnim = 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);
}
//这里使用创建好的目的地Fragment 来replace mContainerId,这个ID是系统内置的R.id.nav_host_fragment_container
ft.replace(mContainerId, frag);
ft.setPrimaryNavigationFragment(frag);
///............此处省略代码
}
///>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
public Fragment instantiateFragment(@NonNull Context context,
@NonNull FragmentManager fragmentManager,
@NonNull String className, @SuppressWarnings("unused") @Nullable Bundle args) {
return fragmentManager.getFragmentFactory().instantiate(
context.getClassLoader(), className);
}
4)、创建目的地实例 FragmentFactory.java instantiate()
通过类加载器来加载第一个目的地的类型；
类构造器构造创建目的地实例。
//FragmentFactory.java
public Fragment instantiate(@NonNull ClassLoader classLoader, @NonNull String className) {
try {
//使用类加载器加载类
Class cls = loadFragmentClass(classLoader, className);
//类构造器构造实例
return cls.getConstructor().newInstance();
} catch (java.lang.InstantiationException e) {
throw new Fragment.InstantiationException("Unable to instantiate fragment " + className
+ ": make sure class name exists, is public, and has an"
+ " empty constructor that is public", e);
} catch (IllegalAccessException e) {
throw new Fragment.InstantiationException("Unable to instantiate fragment " + className
+ ": make sure class name exists, is public, and has an"
+ " empty constructor that is public", e);
} catch (NoSuchMethodException e) {
throw new Fragment.InstantiationException("Unable to instantiate fragment " + className
+ ": could not find Fragment constructor", e);
} catch (InvocationTargetException e) {
throw new Fragment.InstantiationException("Unable to instantiate fragment " + className
+ ": calling Fragment constructor caused an exception", e);
}
}
public static Class loadFragmentClass(@NonNull ClassLoader classLoader,
@NonNull String className) {
try {
Class clazz = loadClass(classLoader, className);
return (Class) clazz;
} catch (ClassNotFoundException e) {
throw new Fragment.InstantiationException("Unable to instantiate fragment " + className
+ ": make sure class name exists", e);
} catch (ClassCastException e) {
throw new Fragment.InstantiationException("Unable to instantiate fragment " + className
+ ": make sure class is a valid subclass of Fragment", e);
}
}
2、导航控制器导航目的地
Navigator导航调用过程
2.1） 从调用开始
Navigation.findNavController(v).navigate(R.id.backtoSecond);
2.2）找到目的地ID
- 根据actionID找到导航视图中对应的Action信息
- 从Action信息中得到新的目的地ID
- 查找目的地ID ,得到对应的NavDestation()
- 导航到新的目的地
//NavController.java
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;
//根据传入的ID找到当前Fragment节点中的action节点信息
final NavAction navAction = currentNode.getAction(resId);
Bundle combinedArgs = null;
if (navAction != null) {
if (navOptions == null) {
navOptions = navAction.getNavOptions();
}
//从action中获取下一个目的地的id
destId = navAction.getDestinationId();
Bundle navActionArgs = navAction.getDefaultArguments();
if (navActionArgs != null) {
combinedArgs = new Bundle();
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");
}
//查找下一目的地
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);
}
}
//导航到新的目的地
navigate(node, combinedArgs, navOptions, navigatorExtras);
}
///>>>>>>>>>>>>>>>>>>>>>>>
NavDestination findDestination(@IdRes int destinationId) {
if (mGraph == null) {
return null;
}
if (mGraph.getId() == destinationId) {
return mGraph;
}
NavDestination currentNode = mBackStack.isEmpty()
? mGraph
: mBackStack.getLast().getDestination();
NavGraph currentGraph = currentNode instanceof NavGraph
? (NavGraph) currentNode
: currentNode.getParent();
return currentGraph.findNode(destinationId);
}
////>>>>>>>>>>>>>>>>>>>
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 navigator = mNavigatorProvider.getNavigator(
node.getNavigatorName());
Bundle finalArgs = node.addInDefaultArgs(args);
//这里进入FragmentNavigator的navigate()中，进行导航
NavDestination newDest = navigator.navigate(node, finalArgs,
navOptions, navigatorExtras);
//.........
}
2.3）类加载器加载新的目的地Fragment
这里和加载第一个目的地Fragment的方式一样，通过类加载器加载目的地Fragment,然后通过替换显示容器将目的地Fragment显示出来。
总结
技术点：类加载、工厂模式、XML---PULL解析