Android架构组件-Navigation的使用(一)
Android架构组件-Navigation的使用(二)
在 Google I/O 2018 上新出现了一个导航组件（Navigation Architecture Component），导航组件类似iOS开发里的StoryBoard，可以可视化的编辑App页面的导航关系。
官方文档：The Navigation Architecture Component
官方教程：Navigation Codelab
学习Demo：navigation
Google实验室的Demo: android-navigation
导航（Navigation）规则
- App需要有确定的起始点
- 使用一个栈来代表App的导航状态
- 向上按钮从不会退出你的App
- 在App任务中向上和返回按钮是等价的
- 深度链接到目标或导航到相同的目标应产生相同的堆栈
Navigation的使用
Navigation 是 Android Studio 3.2 才有的功能，所以要先下载 Android Studio 3.2, 目前 Android Studio 3.2 是预览版，正式版目前是 3.1.3，Android studio3.2/3.3下载页面
Android studio
下载完 Android Studio 3.2 /3.3 后打开项目
在 app 下的 build.gradle 导入 Navigation：
dependencies {
//...
implementation "android.arch.navigation:navigation-fragment-ktx:1.0.0-alpha04"
implementation "android.arch.navigation:navigation-ui-ktx:1.0.0-alpha04"
}
建立个Activity，需要用到 NavHost 来托管 Navigation，NavHost 是个接口，默认是用 NavHostFragment 来托管，NavHostFragment 是实现了 NavHost 接口的，查看 NavHostFragment 会看到，在注释里他已经提供了简单的activity布局写法
/**
* NavHostFragment provides an area within your layout for self-contained navigation to occur.
*
* NavHostFragment is intended to be used as the content area within a layout resource
* defining your app's chrome around it, e.g.:
*
*
* <android.support.v4.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="@xml/nav_sample"
* app:defaultNavHost="true" />
* <android.support.design.widget.NavigationView
* android:layout_width="wrap_content"
* android:layout_height="match_parent"
* android:layout_gravity="start"/>
* </android.support.v4.widget.DrawerLayout>
*
*
* 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.
*
* 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.
*/
public class NavHostFragment extends Fragment implements NavHost {
//...
}
参考例子，我们的NavigationMainActivity布局：
AppBarLayout和Toolbar暂不做介绍
fragment会发现有2分属性：
app:navGraph: 属性赋值的是 nagation 文件
app:defaultNavHost: 这个是和返回键相关的
这个nagation文件是什么呢？我们先来建Fragment和activity：
Menu1Fragment:
class Menu1Fragment : Fragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_menu1, container, false)
}
}
xml:
Menu2Fragment:
class Menu2Fragment : Fragment() {
lateinit var binding: FragmentMenu2Binding
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
// Inflate the layout for this fragment
binding = DataBindingUtil.inflate(inflater, R.layout.fragment_menu2, container, false)
return binding.root
}
}
xml:
Menu2NextFragment此处先省略不写了。
在res目录右键选择new -> Android Resource File
新建个navigation资源文件：
在res目录下会产生navigation文件夹：
会产生这样的文件：
写<左尖括号的时候，会提示：
然后我们将fragment添加进去：
id: 就像写布局的 id 那样需要给个 id 才能找到它
name: 哪个 Fragment 类名
tools:layout: fragment的layout
就像下面写好的这样：
navigation -> nav_garden:
仔细查看代码的话，会发现在navigation下有个app:startDestination，这是给导航指定起始位置的，必须要设置，不然会奔溃报错。
点击下面的Design查看下：
这样我们的app:navGraph="@navigation/nav_garden"就创建好了
结合ToolBar和navigationView
下面新建个menu文件:
这样NavigationView 的app:menu="@menu/menu_navigation"也创建好了。注意menu这里的id需要和navigation的id对应。
activity代码修改为：
class NavigationMainActivity : AppCompatActivity() {
lateinit var binding: ActivityNavigationMainBinding
lateinit var navController: NavController
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = DataBindingUtil.setContentView(this, R.layout.activity_navigation_main)
// Set up ActionBar
setSupportActionBar(binding.toolbar)
navController = Navigation.findNavController(this, R.id.garden_nav_fragment)
NavigationUI.setupActionBarWithNavController(this, navController, binding.drawerLayout)
// Set up navigation menu
binding?.navigationView.setupWithNavController(navController)
}
override fun onSupportNavigateUp(): Boolean {
return NavigationUI.navigateUp(binding.drawerLayout, navController)
}
override fun onBackPressed() {
if(binding.drawerLayout.isDrawerOpen(GravityCompat.START)) {
binding.drawerLayout.closeDrawer(GravityCompat.START)
} else {
super.onBackPressed()
}
}
}
Navigation 可以和 Toolbar 相结合，Toolbar 左边会出现个返回的箭头，这样箭头的显示和隐藏控制都不用我们去写了。
用 Toolbar 的话 Activity 的 style 要设置 NoActionBar 的。
这里用到了 NavigationUI 的setupActionBarWithNavController(AppCompatActivity activity, NavController navController) 方法，还覆盖了 onSupportNavigateUp() 方法。是因为在宿主activity里需要重写onSupportNavigateUp方法去启动fragment。想了解更多的话，可以进入源码查看都做了什么
界面间跳转
看上图右侧，可以添加Arguments(传参),Action(页面间跳转)，我们在Menu2Fragment上添加跳转到Menu2NextFragment：
action的id 和 destination:
id 就是这个 action 的 id,
destination 是目的地，要跳转到哪里的
还可以设置动画
查看design：
Menu2Fragment和Menu2NextFragment之间有根带箭头的线，右侧Action的位置有跳转id。
要跳转到第二个 Fragment 得使用
NavController
来发起页面跳转，可以通过以下方法获取NavController:
NavHostFragment.findNavController(Fragment)Navigation.findNavController(Activity, @IdRes int viewId)Navigation.findNavController(View)
获取到NavController后，就可以通过它的navigate()方法发起页面跳转，navigate()接受action id 或 fragment id 以及导航选项及Bundle参数等作为参数。
/**
* Find a {@link NavController} given the id of a View and its containing
* {@link Activity}. This is a convenience wrapper around {@link #findNavController(View)}.
*
* This method will locate the {@link NavController} associated with this view.
* This is automatically populated for the id of a {@link NavHost} and its children.
*
* @param activity The Activity hosting the view
* @param viewId The id of the view to search from
* @return the {@link NavController} associated with the view referenced by id
* @throws IllegalStateException if the given viewId does not correspond with a
* {@link NavHost} or is not within a NavHost.
*/
@NonNull
public static NavController findNavController(@NonNull Activity activity, @IdRes int viewId) {
View view = ActivityCompat.requireViewById(activity, viewId);
NavController navController = findViewNavController(view);
if (navController == null) {
throw new IllegalStateException("Activity " + activity
+ " does not have a NavController set on " + viewId);
}
return navController;
}
/**
* Find a {@link NavController} given a local {@link View}.
*
* This method will locate the {@link NavController} associated with this view.
* This is automatically populated for views that are managed by a {@link NavHost}
* and is intended for use by various {@link android.view.View.OnClickListener listener}
* interfaces.
*
* @param view the view to search from
* @return the locally scoped {@link NavController} to the given view
* @throws IllegalStateException if the given view does not correspond with a
* {@link NavHost} or is not within a NavHost.
*/
@NonNull
public static NavController findNavController(@NonNull View view) {
NavController navController = findViewNavController(view);
if (navController == null) {
throw new IllegalStateException("View " + view + " does not have a NavController set");
}
return navController;
}
还有一种是通过 NavHostFragment 类
/**
* Find a {@link NavController} given a local {@link Fragment}.
*
* 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)}.
*
* @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.requireFragmentManager()
.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);
}
throw new IllegalStateException("Fragment " + fragment
+ " does not have a NavController set");
}
都是 public static 的方法，所以得到 NavController 之后呢，NavController 有 navigate 方法可以做跳转的
/**
* Navigate to a destination from the current navigation graph. This supports both navigating
* via an {@link NavDestination#getAction(int) action} and directly navigating to a destination.
*
* @param resId an {@link NavDestination#getAction(int) action} id or a destination id to
* navigate to
* @param args arguments to pass to the destination
*/
public final void navigate(@IdRes int resId, @Nullable Bundle args) {
navigate(resId, args, null);
}
这里的参数 resId ,从注释中也知道是 action 的那个 id。所以，给按钮添加事件做跳转
修改Menu2Fragment：
class Menu2Fragment : Fragment() {
lateinit var binding: FragmentMenu2Binding
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
binding = DataBindingUtil.inflate(inflater,R.layout.fragment_menu2, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
binding.btnToSecondFragment.addClickAction {
Navigation.findNavController(view).navigate(R.id.action_livedata_fragment_to_livedata2_fragment)
}
}
}
传递数据
有时候可能要从第一个 Fragment 带些数据去第二个 Fragment，那怎么办，也很简单，navigate 有个俩参数的方法
public final void navigate(@IdRes int resId, @Nullable Bundle args) {
navigate(resId, args, null);
}
第二个参数 Bundle 是经常用的了，跳转后 Activity 可以用 getIntent() 获取，Fragment 可以通过 getArguments() 获取，修改Menu2Fragment的点击事件：
binding.btnToSecondFragment.addClickAction {
var bundle: Bundle = bundleOf(
"test" to getString(R.string.menu2next_args),
"num" to 9
)
Navigation.findNavController(view).navigate(R.id.action_livedata_fragment_to_livedata2_fragment, bundle)
}
Menu2NextFragment：
class Menu2NextFragment : Fragment() {
lateinit var binding: FragmentMenu2NextBinding
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
binding = DataBindingUtil.inflate(inflater, R.layout.fragment_menu2_next, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
var test: String = arguments?.getString("test")?:""
var num: Int = arguments?.getInt("num")?:0
}
}
这里是 Fragment ，跳转后用 getArguments() 去获取
类型安全的方式传递数据
Navigation 还提供了一种安全的数据传递，是怎样的呢？先配置安全插件,在 Project 根目录下的 build.gradle导入：
dependencies {
//...
classpath "android.arch.navigation:navigation-safe-args-gradle-plugin:1.0.0-alpha04"
}
在 app 下的 build.gradle 里 apply, 同步一下 gradle
apply plugin: 'androidx.navigation.safeargs'
配置完成后，我们在nav添加Arguments数据传递：
argument 有三个属性 name、defaultValue 和 type,
- name 就是名字到时会生成这个名字的 set 和 get 方法，
- defaultValue 是默认值，
- type 就是数据类型，有以下几种可以使用
怎么用呢？使用也简单，生成的 argument 的类使用 Builder 模式，这里的数据是从Menu2Fragment 传数据给Menu2NextFragment。
查看生成的Menu2FragmentArgs里的Builder方法：
public static class Builder {
@NonNull
private String test = "@string/menu2next_args";
private int num = 0;
public Builder(Menu2FragmentArgs original) {
this.test = original.test;
this.num = original.num;
}
public Builder() {
}
@NonNull
public Menu2FragmentArgs build() {
Menu2FragmentArgs result = new Menu2FragmentArgs();
result.test = this.test;
result.num = this.num;
return result;
}
@NonNull
public Builder setTest(@NonNull String test) {
if (test == null) {
throw new IllegalArgumentException("Argument \"test\" is marked as non-null but was passed a null value.");
}
this.test = test;
return this;
}
@NonNull
public Builder setNum(int num) {
this.num = num;
return this;
}
@NonNull
public String getTest() {
return test;
}
public int getNum() {
return num;
}
}
使用如下：
var bundle: Bundle = bundleOf(
"test" to getString(R.string.menu2next_args),
"num" to 9
)
var menu2FragmentArgs: Menu2FragmentArgs = Menu2FragmentArgs.Builder(Menu2FragmentArgs.fromBundle(bundle)).build()
Navigation.findNavController(view).navigate(R.id.action_livedata_fragment_to_livedata2_fragment, menu2FragmentArgs.toBundle())
Menu2NextFragment接收：
var menu2FragmentArgs: Menu2FragmentArgs = Menu2FragmentArgs.fromBundle(arguments)
var test: String = menu2FragmentArgs.test
var num: Int = menu2FragmentArgs.num
返回
defaultNavHost 这个属性和返回键有关的，如果把这个属性改为 false，从第一个 Fragment 跳到第二个 Fragment 再按返回键就会直接退出程序。
第二个 Fragment 可以不用按返回键返回第一个 Fragment, 通过 NavController 去控制，修改下Menu2NextFragment的布局，添加个按钮。
class Menu2NextFragment : Fragment() {
//...
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//...
binding.btnBackMenu1Fragment.addClickAction {
Navigation.findNavController(view).popBackStack(R.id.menu2_fragment, false)
}
}
}
NavController 有 navigateUp() 和 popBackStack() 都可以返回上一级，有什么区别:
popBackStack() 如果当前的返回栈是空的就会报错，因为栈是空的了，navigateUp() 则不会，还是停留在当前界面
看看 popBackStack() 源码，第一句就是判断返回栈是不是空的
public boolean popBackStack() {
if (mBackStack.isEmpty()) {
// Nothing to pop if the back stack is empty
return false;
}
// Pop just the current destination off the stack
return popBackStack(getCurrentDestination().getId(), true);
}
查看navigateUp源码，做了判断 返回栈是不是只剩一个，不是的话就会去调用 popBackStack()
public boolean navigateUp() {
if (mBackStack.size() == 1) {
// If there's only one entry, then we've deep linked into a specific destination
// on another task so we need to find the parent and start our task from there
NavDestination currentDestination = getCurrentDestination();
int destId = currentDestination.getId();
NavGraph parent = currentDestination.getParent();
while (parent != null) {
if (parent.getStartDestination() != destId) {
TaskStackBuilder parentIntents = new NavDeepLinkBuilder(NavController.this)
.setDestination(parent.getId())
.createTaskStackBuilder();
parentIntents.startActivities();
if (mActivity != null) {
mActivity.finish();
}
return true;
}
destId = parent.getId();
parent = parent.getParent();
}
// We're already at the startDestination of the graph so there's no 'Up' to go to
return false;
} else {
return popBackStack();
}
}
popBackStack还有个方法
public boolean popBackStack(@IdRes int destinationId, boolean inclusive) {//...}
第一个参数是 Navigation 文件的 fragment 的 id，不是 action 的，
第二个参数是指是否包含第一个参数 id 那个也弹出栈
动态加载Navigation
有时候不想马上启动 Start Destination，或者从别的地方收到传过来的数据，然后要在 Start Destination 中用的需求，这时就不能在 layout 中写 navGraph，因为写了 navGraph 一启动就会去加载 Start Destination，这时可以用代码去动态加载 Navigation 文件的内容，从 NavHostFragment 入手。
- 修改下 Activity 的 layout，把 NavHostFragment 的 navGraph 属性去掉
- 在 Activity 里加载
var navHostFragment: NavHostFragment = supportFragmentManager.findFragmentById(R.id.garden_nav_fragment) as NavHostFragment
var navSimple: NavGraph = navHostFragment.navController.navInflater.inflate(R.navigation.nav_garden)
var menu2FragDestination: NavDestination = navSimple.findNode(R.id.menu2_fragment)
var menu2FragmentArgs: Menu2FragmentArgs = Menu2FragmentArgs.fromBundle(bundleOf("test" to getString(R.string.menu2next_args), "num" to 9))
menu2FragDestination.setDefaultArguments(menu2FragmentArgs.toBundle())
navHostFragment.navController.graph = navSimple
这里先通过 FragmentManager 找到 NavHostFragment，navHostFragment 有 getNavController() 方法，
NavController 里 getNavInflater() 方法获得 NavInflater，
NavInflater 这个类似 LayoutInflater, 通过 inflate() 去加载 Navigation，
设置了数据后通过 NavController 的 setGraph(NavGraph graph) 就加载出来了
参考文章：
- Android Navigation Architecture Component 使用详解
- Android官方架构组件Navigation：大巧不工的Fragment管理框架
- 导航库 Navigation 小结