原理：Jetpack Navigation 原理浅析

Navigation 的基本使用

gradle 库导入根据Java 或者 Kotlin 需求导入

dependencies {
  def nav_version = "2.3.2"

  // Java language implementation
  implementation "androidx.navigation:navigation-fragment:$nav_version"
  implementation "androidx.navigation:navigation-ui:$nav_version"

  // Kotlin
  implementation "androidx.navigation:navigation-fragment-ktx:$nav_version"
  implementation "androidx.navigation:navigation-ui-ktx:$nav_version"

  // Feature module Support
  implementation "androidx.navigation:navigation-dynamic-features-fragment:$nav_version"

  // Testing Navigation
  androidTestImplementation "androidx.navigation:navigation-testing:$nav_version"

  // Jetpack Compose Integration
  implementation "androidx.navigation:navigation-compose:1.0.0-alpha05"
}

创建 navigation graph

可以用AS界面，也可以手动创建

res/navigation/nav_graph.xml

<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"
    app:startDestination="@id/mainPage1Fragment">

    <fragment
        android:id="@+id/mainPage1Fragment"
        android:name="top.zcwfeng.jetpack.navigation.MainPage1Fragment"
        android:label="fragment_main_page1"
        tools:layout="@layout/fragment_main_page1" >
        <action
            android:id="@+id/fragment1_2"
            app:destination="@id/mainPage2Fragment" />
    </fragment>
    <fragment
        android:id="@+id/mainPage2Fragment"
        android:name="top.zcwfeng.jetpack.navigation.MainPage2Fragment"
        android:label="fragment_main_page2"
        tools:layout="@layout/fragment_main_page2" >
        <action
            android:id="@+id/fragment2_3"
            app:destination="@id/mainPage3Fragment" />
    </fragment>
    <fragment
        android:id="@+id/mainPage3Fragment"
        android:name="top.zcwfeng.jetpack.navigation.MainPage3Fragment"
        android:label="fragment_main_page3"
        tools:layout="@layout/fragment_main_page3" >
        <action
            android:id="@+id/fragment3_2"
            app:destination="@id/mainPage2Fragment" />
    </fragment>
</navigation>

重点看下这几个属性

navigation ---->android:id 和 app:startDestination 声明
fragment ------> id,name,label
fragment 子标签 action----> id,app:destination

添加 NavHost 到 activity

主要的NavigationActivity的activity_navigation.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
    tools:context=".navigation.NavigationActivity">
    <fragment
        android:id="@+id/fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="409dp"
        android:layout_height="729dp"
        app:defaultNavHost="true"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:navGraph="@navigation/nav_graph" />
</androidx.constraintlayout.widget.ConstraintLayout>

指定navigation文件
app:navGraph="@navigation/nav_graph"
主容器fragment
android:name="androidx.navigation.fragment.NavHostFragmen"
app:defaultNavHost="true" 拦截系统back键

官网API

新版的官网可以用 FragmentContainerView，查看源码也是instantiate一个实例fragment，大同小异

添加 destinations 到 navigation graph
导航到目标

底部导航切换的做法

BottomNavigationView bottomNavigationView = findViewById(R.id.fragment1_2)...;

NavController 创建两种方式

1. NavController controller=Navigation.findNavController(this,R.id.fragment_nav_host);

2.  NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.fragment_nav_host);
 NavController controller = navHostFragment.getNavController();

controller 绑定到底部导航View（MaterialDesign中）
NavigationUI.setupWithNavController(bottomNavigationView,controller);

回退到上一步的api

Navigation.findNavController(view).navigateUp();
或者指定目标
Navigation.findNavController(view).navigate(R.id.action_page2);

Jetpack(一)Lifecycle和LiveData
JetPacks之Lifecycles原理
JetPack之 LifeCycle LiveData

Jetpack(二)之DataBinding

Jetpack(三) 之 Room 与 ViewModel
Jetpack 之 ViewModel 原理

Jetpack (四) 之 Navigation
Jetpack Navigation 原理浅析

JetPack （五）之 Paging 分页库

Jetpack(六) 之 WorkManager
Jetpack WorkManager 原理

Jetpack (四) 之 Navigation

Navigation 的 基本使用

Navigation 的基本使用