Android Navigation 學習筆記

為什麼要用Navigation？

當你專案中的頁面越來越多，Fragment和Activity之間的跳轉越來越繁雜，是不是搞得你一團亂呢？你是否羨慕Xcode中能將頁面跳轉視覺化的Storyboard呢？

Xcode Storyboard

好在Google終於提供了Navigation套件來幫我們處理這些問題，讓我們一起來試玩看看吧。

Android Navigation Graph

環境設定

如果你的Android Studio版本是3.2的話，必須到Setting將Navigation Editor打開，3.3以上版本無需此動作

enable Navigation Editor

dependencies

首先設定module層的build.gradle，我的Demo會用androidx的版本示範

androidx version
dependencies {
    implementation "androidx.navigation:navigation-fragment:2.0.0"
    implementation "androidx.navigation:navigation-ui:2.0.0"
}

新建三個Fragment

class MainPage1Fragment : Fragment() {

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View {
        return inflater.inflate(R.layout.fragment_main_page1, container, false)
    }
}

class MainPage2Fragment : Fragment() {

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.fragment_main_page2, container, false)
    }
}

class MainPage3Fragment : Fragment() {

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.fragment_main_page3, container, false)
    }
}

Navigation Graph

在resource建立navigation資料夾

新增Navigation Graph xml

空白的Navigation Graph

打開Navigation文件，我們可以在AndroidStudio 3.2版本上，進行可視化編輯，包括選擇新增Fragment，或者拖拽，連接Fragment：

編輯Navigation文件

<?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"
    app:startDestination="@id/page1Fragment">

    <fragment
        android:id="@+id/page1Fragment"
        android:name="com.qingmei2.samplejetpack.ui.main.MainPage1Fragment"
        android:label="fragment_page1"
        tools:layout="@layout/fragment_main_page1">
        <action
            android:id="@+id/action_page2"
            app:destination="@id/page2Fragment" />
    </fragment>

    <fragment
        android:id="@+id/page2Fragment"
        android:name="com.qingmei2.samplejetpack.ui.main.MainPage2Fragment"
        android:label="fragment_page2"
        tools:layout="@layout/fragment_main_page2">
        <action
            android:id="@+id/action_page1"
            app:popUpTo="@id/page1Fragment" />
        <action
            android:id="@+id/action_page3"
            app:destination="@id/nav_graph_page3" />
    </fragment>

    <navigation
        android:id="@+id/nav_graph_page3"
        app:startDestination="@id/page3Fragment">
        <fragment
            android:id="@+id/page3Fragment"
            android:name="com.qingmei2.samplejetpack.ui.main.MainPage3Fragment"
            android:label="fragment_page3"
            tools:layout="@layout/fragment_main_page3" />
    </navigation>

</navigation>

編輯MainActivity

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <fragment
        android:id="@+id/my_nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph_main" />

</android.support.constraint.ConstraintLayout>

這之後，在Activity中添加如下代碼：

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    override fun onSupportNavigateUp() =
            findNavController(this, R.id.my_nav_host_fragment).navigateUp()
}

onSupportNavigateUp()方法的重寫，意味著Activity將它的back鍵點擊事件的委託出去，如果當前並非棧中頂部的Fragment,那麼點擊back鍵，返回上一個Fragment。

最後，配置不同Fragment對應的跳轉事件

class MainPage1Fragment : Fragment() {
     //隐藏了onCreateView()方法的實現，下同
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        btn.setOnClickListener {
            //點擊跳轉page2
            Navigation.findNavController(it).navigate(R.id.action_page2)
        }
    }
}

class MainPage2Fragment : Fragment() {

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        btn.setOnClickListener {
           //點擊跳轉page1
            Navigation.findNavController(it).navigateUp()
        }
        btn2.setOnClickListener {
            //點擊跳轉page3
            Navigation.findNavController(it).navigate(R.id.action_page3)
        }
    }
}

class MainPage3Fragment : Fragment() {

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        //點擊跳轉page2
        btn.setOnClickListener { Navigation.findNavController(it).navigateUp() }
    }
}

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HulkYang's Android Notes