一、Navigation

1、Navigation 概述

• Navigation 是 Jetpack 中的一个重要成员，它主要是结合导航图（Navigation Graph）来控制和简化 Fragment 之间的导航，即往哪里走，该怎么走

2、Navigate 引入

• 在模块级 build.gradle 中引入相关依赖

implementation 'androidx.navigation:navigation-fragment:2.3.5'
implementation 'androidx.navigation:navigation-ui:2.3.5'

---

二、Navigation 跳转实例实操

• 有三个 Fragment 实现 Navigation 跳转，它们分别是 MoreJumpOneFragment、MoreJumpTwoFragment、MoreJumpThreeFragment

1. 在 MoreJumpOneFragment 中，可以前进到 MoreJumpTwoFragment

2. 在 MoreJumpTwoFragment 中，可以前进到 MoreJumpThreeFragment，也可以后退到 MoreJumpOneFragment

3. 在 MoreJumpThreeFragment 中，可以后退到 MoreJumpTwoFragment，也可以直接后退到 MoreJumpOneFragment

2、具体实现

（1）Fragment Layout

1. fragment_more_jump_one.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=".fragment.MoreJumpOneFragment">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="MoreJumpOneFragment"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btn_go"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="前进"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

2. fragment_more_jump_two.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=".fragment.MoreJumpTwoFragment">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="MoreJumpTwoFragment"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btn_go"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="前进"
        app:layout_constraintBottom_toTopOf="@+id/btn_back"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

    <Button
        android:id="@+id/btn_back"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="后退"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

3. fragment_more_jump_three.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=".fragment.MoreJumpThreeFragment">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="MoreJumpThreeFragment"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btn_back"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="后退"
        app:layout_constraintBottom_toTopOf="@+id/btn_back_to_one"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

    <Button
        android:id="@+id/btn_back_to_one"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="后退到 one"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

（2）Fragment Code

1. MoreJumpOneFragment.java

package com.my.navigation.fragment;

import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

import com.my.navigation.R;

public class MoreJumpOneFragment extends Fragment {

    private NavController navController;

    private Button btnGo;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_more_jump_one, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        navController = Navigation.findNavController(view);

        btnGo = view.findViewById(R.id.btn_go);

        btnGo.setOnClickListener(v -> navController.navigate(R.id.action_moreJumpOneFragment_to_moreJumpTwoFragment));
    }
}

2. MoreJumpTwoFragment.java

package com.my.navigation.fragment;

import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

import com.my.navigation.R;

public class MoreJumpTwoFragment extends Fragment {

    private NavController navController;

    private Button btnGo;
    private Button btnBack;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_more_jump_two, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        navController = Navigation.findNavController(view);

        btnGo = view.findViewById(R.id.btn_go);
        btnBack = view.findViewById(R.id.btn_back);

        btnGo.setOnClickListener(v -> navController.navigate(R.id.action_moreJumpTwoFragment_to_moreJumpThreeFragment));

        btnBack.setOnClickListener(v -> navController.navigateUp());
    }
}

3. MoreJumpThreeFragment.java

package com.my.navigation.fragment;

import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

import com.my.navigation.R;

public class MoreJumpThreeFragment extends Fragment {

    private NavController navController;

    private Button btnBack;
    private Button btnBackToOne;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_more_jump_three, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        navController = Navigation.findNavController(view);

        btnBack = view.findViewById(R.id.btn_back);
        btnBackToOne = view.findViewById(R.id.btn_back_to_one);

        btnBack.setOnClickListener(v -> navController.navigateUp());

        btnBackToOne.setOnClickListener(v -> navController.popBackStack(R.id.moreJumpOneFragment, false));
    }
}

（3）Navigation Graph

• my_graph_more_jump.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/my_graph_more_jump"
    app:startDestination="@id/moreJumpOneFragment">

    <fragment
        android:id="@+id/moreJumpOneFragment"
        android:name="com.my.navigation.fragment.MoreJumpOneFragment"
        android:label="fragment_more_jump_one"
        tools:layout="@layout/fragment_more_jump_one">
        <action
            android:id="@+id/action_moreJumpOneFragment_to_moreJumpTwoFragment"
            app:destination="@id/moreJumpTwoFragment" />
    </fragment>
    <fragment
        android:id="@+id/moreJumpTwoFragment"
        android:name="com.my.navigation.fragment.MoreJumpTwoFragment"
        android:label="fragment_more_jump_two"
        tools:layout="@layout/fragment_more_jump_two">
        <action
            android:id="@+id/action_moreJumpTwoFragment_to_moreJumpThreeFragment"
            app:destination="@id/moreJumpThreeFragment" />
    </fragment>
    <fragment
        android:id="@+id/moreJumpThreeFragment"
        android:name="com.my.navigation.fragment.MoreJumpThreeFragment"
        android:label="fragment_more_jump_three"
        tools:layout="@layout/fragment_more_jump_three">
        <action
            android:id="@+id/action_moreJumpThreeFragment_to_moreJumpOneFragment"
            app:destination="@id/moreJumpOneFragment" />
    </fragment>
</navigation>

（4）Activity Layout

• activity_more_jump.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=".MoreJumpActivity">

    <fragment
        android:id="@+id/nhf"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:navGraph="@navigation/my_graph_more_jump" />
</androidx.constraintlayout.widget.ConstraintLayout>

（5）Activity Code

• MoreJumpActivity.java

package com.my.navigation;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

public class MoreJumpActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_more_jump);
    }
}

---

三、Navigation 跳转详解

1、Navigation 跳转方法

1. void navigate(@IdRes int resId)：该方法用于根据在导航图中定义的 action 的 ID 进行 Fragment 跳转

2. boolean navigateUp()：该方法用于返回到上一个 Fragment

3. boolean popBackStack(@IdRes int destinationId, boolean inclusive)：该方法用于活动栈中弹出 Fragment，直到到达指定的 Fragment，如果 inclusive 被设置为 true，则指定的 Fragment 也会被从活动栈中移除

2、Navigation 活动栈解析

1. 一开始在 MoreJumpOneFragment 中时，此时的活动栈

MoreJumpOneFragment

2. 当在 MoreJumpOneFragment 中，前进到 MoreJumpTwoFragment 时，此时的活动栈

MoreJumpTwoFragment
MoreJumpOneFragment

3. 当在 MoreJumpTwoFragment 中，前进到 MoreJumpThreeFragment 时，此时的活动栈

MoreJumpThreeFragment
MoreJumpTwoFragment
MoreJumpOneFragment

4. 当在 MoreJumpThreeFragment 中，后退到 MoreJumpOneFragment 时，此时的活动栈

MoreJumpThreeFragment

---

四、Navigation 跳转补充

1、Navigation 跳转方法补充

• 在 MoreJumpThreeFragment 中，直接后退到 MoreJumpOneFragme，除了使用 popBackStack 方法，还可以用如下方法

NavOptions navOptions = new NavOptions.Builder().setPopUpTo(R.id.moreJumpOneFragment, true).build();
navController.navigate(R.id.action_moreJumpThreeFragment_to_moreJumpOneFragment, null, navOptions);

2、Navigation 跳转方法解析

NavOptions navOptions = new NavOptions.Builder().setPopUpTo(R.id.moreJumpOneFragment, true).build();

• 使用 NavOptions.Builder 创建一个 NavOptions 对象，它是跳转行为

1. 该对象指定了在导航到 moreJumpOneFragment 时，清除活动栈中所有 moreJumpOneFragment 之上的 Fragment

2. 其中，Builder setPopUpTo(@IdRes int destinationId, boolean inclusive) 方法中的 inclusive 被设置为 true，表示包括 moreJumpOneFragment 本身也被清除

3. 因为要跳转到 moreJumpOneFragment，所以并不会真正导致 moreJumpOneFragment 从活动栈中被清楚，但所有在它之上的 Fragment 都会被清除，导致看起来就像是直接跳转到了moreJumpOneFragment

navController.navigate(R.id.action_moreJumpThreeFragment_to_moreJumpOneFragment, null, navOptions);

• 通过 void navigate(@IdRes int resId, @Nullable Bundle args, @Nullable NavOptions navOptions) 方法进行跳转，需要传递 3 个参数，分别为导航图中定义的 action 的 ID、携带数据、跳转行为