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 在 Activity 中的使用
1、需求
-
在 Activity 中实现两个 Fragment 之间的导航，从 Fragment1 跳转到 Fragment2，从 Fragment2 返回 Fragment1
-
其中，Activity 包含一个按钮控制跳转到 Fragment2，Fragment2 包含返回按钮
2、具体实现
（1）Fragment Layout
- fragment_navigation_jump1.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.NavigationJump1Fragment">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="1"
android:textSize="20sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
- fragment_navigation_jump2.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.NavigationJump2Fragment">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="2"
android:textSize="20sp"
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_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
（2）Fragment Code
- NavigationJump1Fragment.java
package com.my.navigation.fragment;
import android.os.Bundle;
import androidx.fragment.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import com.my.navigation.R;
public class NavigationJump1Fragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_navigation_jump1, container, false);
}
}
- NavigationJump2Fragment.java
package com.my.navigation.fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import com.my.navigation.R;
public class NavigationJump2Fragment extends Fragment {
private NavController navController;
private Button btnBack;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_navigation_jump2, 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);
btnBack.setOnClickListener(v -> navController.navigateUp());
}
}
（3）Navigation Graph
- my_graph_navigation_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_jump"
app:startDestination="@id/navigationJump1Fragment">
<fragment
android:id="@+id/navigationJump1Fragment"
android:name="com.my.navigation.fragment.NavigationJump1Fragment"
android:label="fragment_navigation_jump1"
tools:layout="@layout/fragment_navigation_jump1">
<action
android:id="@+id/action_navigationJump1Fragment_to_navigationJump2Fragment"
app:destination="@id/navigationJump2Fragment" />
</fragment>
<fragment
android:id="@+id/navigationJump2Fragment"
android:name="com.my.navigation.fragment.NavigationJump2Fragment"
android:label="fragment_navigation_jump2"
tools:layout="@layout/fragment_navigation_jump2"></fragment>
</navigation>
（4）Activity Layout
- activity_navigation_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=".NavigationJumpActivity"
tools:ignore="MissingConstraints">
<fragment
android:id="@+id/nhf"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="400dp"
app:navGraph="@navigation/my_graph_navigation_jump" />
<Button
android:id="@+id/btn_go_to_2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="跳转到 2"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
（5）Activity Code
- NavigationJumpActivity.java
package com.my.navigation;
import androidx.appcompat.app.AppCompatActivity;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import android.os.Bundle;
import android.widget.Button;
public class NavigationJumpActivity extends AppCompatActivity {
private NavController navController;
private Button btnGoTo2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_navigation_jump);
navController = Navigation.findNavController(this, R.id.nhf);
btnGoTo2 = findViewById(R.id.btn_go_to_2);
btnGoTo2.setOnClickListener(v -> navController.navigate(R.id.navigationJump2Fragment));
}
}
三、Navigation findNavController 方法
public static NavController findNavController(@NonNull View view)
- 主要在 Fragment 内部使用，通过 Fragment 的视图层级查找关联的 NavController
-
参数：Fragment 的根视图，即 onCreateView 方法返回的 View 对象
-
原理：从视图的父级向上查找最近的 NavHostFragment
public static NavController findNavController(@NonNull Activity activity, @IdRes int viewId)
- 主要在 Activity 内部 使用，通过 NavHostFragment 的容器 ID 查找
-
参数：activity 是宿主 Activity，viewId 是布局中 NavHostFragment 的容器 ID
-
原理：通过 FragmentManager 查找指定 ID 的 NavHostFragment