最近在学习Jetpack全组件实战，记录一下其中相关知识点。
Navigation工作流程
从NavHostFragment开始，它是一个内容承载容器，从它的onCreate()方法开始看起：
@CallSuper
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final Context context = requireContext();
//A-1 -- NavHostController页面导航，页面跳转核心类 一个入口
//在这里将内容切换的能力委托给了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());
//A-2 -- onCreateNavController
onCreateNavController(mNavController);
...
}
@CallSuper
protected void onCreateNavController(@NonNull NavController navController) {
//3.DialogFragmentNavigator
navController.getNavigatorProvider().addNavigator(
new DialogFragmentNavigator(requireContext(), getChildFragmentManager()));
//4.FragmentNavigator
navController.getNavigatorProvider().addNavigator(createFragmentNavigator());
}
protected Navigator<? extends FragmentNavigator.Destination> createFragmentNavigator() {
return new FragmentNavigator(requireContext(), getChildFragmentManager(), getId());
}
//NavHostController.java
public NavHostController(@NonNull Context context) {
super(context);
}
//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();
}
//1.NavGraphNavigator 注意其构造函数中又把NavigatorProvider传递了进去
mNavigatorProvider.addNavigator(new NavGraphNavigator(mNavigatorProvider));
//2.ActivityNavigator
mNavigatorProvider.addNavigator(new ActivityNavigator(mContext));
}
NavController
再NavHostFragment的onCreate()方法中，将内容切换的能力委托给了NavHostController，先是创建了一个NavHostController，接着调用了 onCreateNavController 方法。其中一共添加了4个Navigator（两个方法各添加了2个）进去，Navigator，顾名思义，是导航器的意思，这四个导航器分别有着不同的职责：
- NavGraphNavigator —— 当页面资源信息被解析完成之后，会通过它跳转到配置的默认启动页，也就是第一个也页面。
-
ActivityNavigator —— 给
Activity提供跳转、切换的能力。 - **DialogFragmentNavigator ** —— 给
DialogFragment提供跳转、切换的能力。 -
FragmentNavigator —— 给
Fragment提供跳转、切换的能力。
代码中的 mNavigatorProvider 内部其实是通过 HashMap 以键值对的形式存储了一个个导航器（Navigator）。
//NavigatorProvider.java
public class NavigatorProvider {
private final HashMap<String, Navigator<? extends NavDestination>> mNavigators =
new HashMap<>();
public final Navigator<? extends NavDestination> addNavigator(
@NonNull Navigator<? extends NavDestination> navigator) {
//去取Navigator的NAME注解
String name = getNameForNavigator(navigator.getClass());
return addNavigator(name, navigator);
}
public Navigator<? extends NavDestination> addNavigator(@NonNull String name,
@NonNull Navigator<? extends NavDestination> navigator) {
if (!validateName(name)) {
throw new IllegalArgumentException("navigator name cannot be an empty string");
}
return mNavigators.put(name, navigator);
}
@NonNull
static String getNameForNavigator(@NonNull Class<? extends Navigator> navigatorClass) {
String name = sAnnotationNames.get(navigatorClass);
if (name == null) {
Navigator.Name annotation = navigatorClass.getAnnotation(Navigator.Name.class);
name = annotation != null ? annotation.value() : null;
if (!validateName(name)) {
throw new IllegalArgumentException("No @Navigator.Name annotation found for "
+ navigatorClass.getSimpleName());
}
sAnnotationNames.put(navigatorClass, name);
}
return name;
}
...
}
Navigator
//Navigator.java
//需要传递一个NavDestination类型的泛型 -- 其作用是为了限定一种Navigator只能创建一种Destination节点信息。
//一个Destination可以代表一个个的页面（activity、fragment、dialog等）
public abstract class Navigator<D extends NavDestination> {
/**
* This annotation should be added to each Navigator subclass to denote the default name used
* to register the Navigator with a {@link NavigatorProvider}.
* 应该将此注释添加到每个Navigator子类中，以表示用{@link NavigatorProvider}注册导航器时使用的默认名称。
*
* 作用：
* 1. 用于NavigatorProvider中存储Navigator所需的key值,value为Navigator本身。
* 2. 用于Destination中的跳转（跳转需是要根据key值去取相应的Destination）
*
*
* @see NavigatorProvider#addNavigator(Navigator)
* @see NavigatorProvider#getNavigator(Class)
*/
@Retention(RUNTIME)
@Target({TYPE})
@SuppressWarnings("UnknownNullness") // TODO https://issuetracker.google.com/issues/112185120
public @interface Name {
String value();
}
// 具体的页面跳转
public abstract NavDestination navigate(@NonNull D destination, @Nullable Bundle args,
@Nullable NavOptions navOptions, @Nullable Extras navigatorExtras);
//需不需要拦截系统返回键，来做一些回退栈的操作
public abstract boolean popBackStack();
//状态保存
@Nullable
public Bundle onSaveState() {
return null;
}
//状态恢复
public void onRestoreState(@NonNull Bundle savedState) {
}
/**
* Interface indicating that this class should be passed to its respective
*
* {@link Navigator} to enable Navigator specific behavior. 跳转时可以提供一些额外的行为，如过度元素，转场动画等。
*/
public interface Extras {
}
}
public class NavDestination {
public NavDestination(@NonNull String navigatorName) {
mNavigatorName = navigatorName;
}
}
ActivityNavigator
//ActivityNavigator.java
@Navigator.Name("activity")
public class ActivityNavigator extends Navigator<ActivityNavigator.Destination> {
@NonNull
@Override
public Destination createDestination() {
//一个静态内部类
return new Destination(this);
}
@Nullable
@Override
public NavDestination navigate(@NonNull Destination destination, @Nullable Bundle args,
@Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {
if (destination.getIntent() == null) {
throw new IllegalStateException("Destination " + destination.getId()
+ " does not have an Intent set.");
}
Intent intent = new Intent(destination.getIntent());
...
if (navigatorExtras instanceof Extras) {
Extras extras = (Extras) navigatorExtras;
ActivityOptionsCompat activityOptions = extras.getActivityOptions();
//启动Activity
if (activityOptions != null) {
ActivityCompat.startActivity(mContext, intent, activityOptions.toBundle());
} else {
mContext.startActivity(intent);
}
} else {
mContext.startActivity(intent);
}
...
// You can't pop the back stack from the caller of a new Activity,
// so we don't add this navigator to the controller's back stack
return null;
}
}
DialogFragmentNavigator
DeepLink源码简析
先看NavController.handleDeepLink(new Intent())方法：
//NavController.java
public boolean handleDeepLink(@Nullable Intent intent) {
if (intent == null) {
return false;
}
Bundle extras = intent.getExtras();
int[] deepLink = extras != null ? extras.getIntArray(KEY_DEEP_LINK_IDS) : null;
Bundle bundle = new Bundle();
Bundle deepLinkExtras = extras != null ? extras.getBundle(KEY_DEEP_LINK_EXTRAS) : null;
if (deepLinkExtras != null) {
bundle.putAll(deepLinkExtras);
}
//intent.getData() 即为所传递过来的uri
if ((deepLink == null || deepLink.length == 0) && intent.getData() != null) {
NavDestination.DeepLinkMatch matchingDeepLink = mGraph.matchDeepLink(intent.getData());
if (matchingDeepLink != null) {
//buildDeepLinkIds() --> 构建DeepLinkIds,包含了从根节点到当前节点的id数组
deepLink = matchingDeepLink.getDestination().buildDeepLinkIds();
bundle.putAll(matchingDeepLink.getMatchingArgs());
}
}
...
if ((flags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
// Start with a cleared task starting at our root when we're on our own task
if (!mBackStack.isEmpty()) {
popBackStackInternal(mGraph.getId(), true);
}
int index = 0;
//遍历deepLinkIds数组
while (index < deepLink.length) {
int destinationId = deepLink[index++];
//每一个NavDestination代表着一个页面
NavDestination node = findDestination(destinationId);
if (node == null) {
throw new IllegalStateException("unknown destination during deep link: "
+ NavDestination.getDisplayName(mContext, destinationId));
}
//通过navigate方法将所涉及的页面一个一个打开
navigate(node, bundle,
new NavOptions.Builder().setEnterAnim(0).setExitAnim(0).build(), null);
}
return true;
}
...
}
//NavDestination.java
/**
* Build an array containing the hierarchy from the root down to this destination.
* 构建一个包含从根到此目的地的层次结构的数组。
* @return An array containing all of the ids from the root to this destination
*/
@NonNull
int[] buildDeepLinkIds() {
ArrayDeque<NavDestination> hierarchy = new ArrayDeque<>();
NavDestination current = this;
do {
NavGraph parent = current.getParent();
if (parent == null || parent.getStartDestination() != current.getId()) {
hierarchy.addFirst(current);
}
current = parent;
} while (current != null);
int[] deepLinkIds = new int[hierarchy.size()];
int index = 0;
for (NavDestination destination : hierarchy) {
deepLinkIds[index++] = destination.getId();
}
return deepLinkIds;
}
举例：
handleDeepLink.png
如果外部应用打开客户端并携带了uri: ppjoke://page/pageD ,那么 A、B、C、D都会被打开 。[图片上传中...(handleDeepLink.png-45632e-1580650536653-0)]
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