Android Jetpack-Navigation（一）

1 Introduction

Navigation is a library and a plug-in simplifies navigation of Android.

Navigation Fragment is used to manage the handover, and can be visualized by the way, we see the interaction process App.

2. advantage

The process switching Fragment
By default, the correct handling of Fragment forward and back
Provides standardized transition and animation resources
Implementation and handling deep connection
You can bind Toolbar, BottomNavigationView and ActionBar
ViewModel support

3. Prepare

AndroidStudio 3.2 or higher

4. Navigation three elements

noun	Explanation
Nvigtiodargrf	This is a new resource file, the user can see the Destination it can reach (the user can reach the screen interface), as well as the relationship between processes visual interface
NavHostFragment	The current fragment of container
NavController	Navigation controller

5. Use

1. Add dependence

implementation group: 'androidx.navigation', name: 'navigation-fragment', version: '2.2.0'
implementation group: 'androidx.navigation', name: 'navigation-ui', version: '2.2.0'

2. Create NavigationGraph

Create a new file in the directory res folder navigation, right-click on the Create New Navigation resource file.

Here Insert Picture Description

Destinations：

HOST: i.e. on the table NavHostFragment, i.e. containers fragment

GRAPH: f is the current vessel fragment

app:startDestinationThe default starting position

android:name: Fragment of the full package name

tools:layout: Fragment layout file

action

android:id: References this id in the jump fragment of

android:destination: Destination, on behalf of this action is to jump to the destination from this fragment represented by fragment

android:popUpTo: This represents, the stack until specified fragment popUpTo

3. Establish NavHostFragment

That is the second step of HOST, which is the current fragment of container

<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=".LoginActivity">

    <fragment
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/nav_activity"
        app:navGraph = "@navigation/welcome_navigation"
        app:defaultNavHost = "true"
        android:name="androidx.navigation.fragment.NavHostFragment"
        />


</androidx.constraintlayout.widget.ConstraintLayout>

Attributes	Explanation
android:name	The value must be androidx.navigation.fragment.NavHostFragment
android:navGraph	存放的是第二步建好的导航资源文件，也就是确定了NavigationGraph
app:defaultNavHost=“true”	与系统的返回按钮相关联

6. 处理跳转

跳转通过NavController对象，它有三种获取方法：

NavHostFragment.findNavController(Fragment);
Navigation.findController(Activity,@IdRes int viewId);
Navigation.findController(View);

调用NavController的navigate方法执行跳转，navigate的参数可以是一个destination（这里就是fragment在导航图nav_graph中的id），也可以是action的id

7. 演示

welcome_navigation.xml

<?xml version="1.0" encoding="utf-8"?>
<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/welcome_navigation"
    app:startDestination="@id/firstFragment">

    <fragment
        android:id="@+id/firstFragment"
        android:name="com.example.navigationproject.FirstFragment"
        android:label="fragment_first"
        tools:layout="@layout/fragment_first"
        >
        <action
            android:id="@+id/action_firstFragment_to_secondFragment"
            app:destination="@id/secondFragment"
            app:enterAnim="@anim/fragment_close_enter"
            app:exitAnim="@anim/fragment_close_exit"
            app:popEnterAnim="@anim/nav_default_pop_enter_anim"
            app:popExitAnim="@anim/nav_default_pop_exit_anim" />
        <action
            android:id="@+id/action_firstFragment_to_thirdFragment"
            app:destination="@id/thirdFragment"
            />
    </fragment>
    <fragment
        android:id="@+id/secondFragment"
        android:name="com.example.navigationproject.SecondFragment"
        android:label="fragment_second"
        tools:layout="@layout/fragment_second" >
        <action
            android:id="@+id/action_secondFragment_to_blankFragment2"
            app:destination="@id/blankFragment2"
            app:enterAnim="@anim/fragment_close_enter"
            app:exitAnim="@anim/fragment_close_exit"
            app:popEnterAnim="@anim/nav_default_pop_enter_anim"
            app:popExitAnim="@anim/nav_default_pop_exit_anim" />
    </fragment>
    <fragment
        android:id="@+id/thirdFragment"
        android:name="com.example.navigationproject.ThirdFragment"
        android:label="fragment_third"
        tools:layout="@layout/fragment_third" />
    <fragment
        android:id="@+id/blankFragment2"
        android:name="com.example.navigationproject.BlankFragment"
        android:label="fragment_blank"
        tools:layout="@layout/fragment_blank" >
        <action
            android:id="@+id/backToFirst"
            app:popUpTo="@id/firstFragment"/>
        <action
            android:id="@+id/aBackToFirst"
            app:destination="@id/firstFragment"
            app:enterAnim="@anim/fragment_close_enter"
            app:exitAnim="@anim/fragment_close_exit"
            app:popEnterAnim="@anim/nav_default_pop_enter_anim"
            app:popExitAnim="@anim/nav_default_pop_exit_anim" />
    </fragment>
</navigation>