Android jetpack : Navigation 导航 路由 、 单个Activity嵌套多个Fragment的UI架构方式

Android Navigation 如何动态的更换StartDestination &&保存Fragment状态

Navigation(一)基础入门

google 官网 : Navigation 导航 路由

讨论了两年的 Navigation 保存 Fragment 状态问题居然被关闭了

Navigation是一种导航的概念,即把Activityfragment当成一个个的目的地Destination,各目的地形成一张导航图NavGraph,由导航控制器NavController来统一调度跳转

单个Activity嵌套多个Fragment的UI架构方式,已被大多数Android工程师所接受和采用。但是,对Fragment的管理一直是一个比较麻烦的事情,工程师需要通过FragmentManager和FragmentTransaction来管理Fragment之间的切换。这其中还包括了对应用程序的App bar的管理,Fragment间的切换动画,Fragment间的参数传递,总之,使用起来不是特别友好。

为此,Android Jetpack提供的一个名为Navigation的UI架构组件。旨在方便我们管理Fragment页面。它具体有以下优势:

  • 可视化的页面导航图,类似xcode中的StoryBoard,便于我们看清页面之间的关系
  • 通过destination和action来完成页面间的导航
  • 方便的页面切换动画
  • 页面间类型安全的参数传递
  • 通过NavigationUI类,对菜单,底部导航,抽屉菜单导航进行方便统一的管理
  • 深层链接

注意:在Android Studio3.2及以上版本才能支持Navigation特性。
本文所说的“页面”包括了Fragment和Activity,但主要是Fragment,因为Navigation组件的主要目地就是方便我们在一个Activity中对多个Fragment进行管理。
首先,我们需要先对Navigation有一个大致的了解。

Navigation Graph

这是一种新型的XML资源文件,里面包含了应用程序所有的页面及页面之间的关系

NavHostFragment

这是一个特殊的布局文件,Navigation Graph中的页面通过该Fragment展示

NavController

这是一个Java/Kotlin对象,用于在代码中完成Navigation Graph中具体的页面切换

当你想要切换页面的时候,使用NavController对象,告诉它你想要去Navigation Graph中的哪个页面,NavController会将相关的页面展示在NavHostFragment中。

创建工程,引入依赖,

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.3"

    defaultConfig {
        applicationId "com.xq.mybottomnavigation"
        minSdkVersion 29
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"
    }

    buildFeatures {
        viewBinding true
    }
}

dependencies {
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.2.1'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.1'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'

    implementation 'androidx.lifecycle:lifecycle-livedata-ktx:2.2.0'
    implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.2.0'

    implementation 'androidx.navigation:navigation-fragment:2.0.0'
    implementation 'androidx.navigation:navigation-ui:2.0.0'
}

MainActivity和布局 :

import android.os.Bundle;

import com.google.android.material.bottomnavigation.BottomNavigationView;

import androidx.appcompat.app.AppCompatActivity;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;

import com.xq.mybottomnavigation.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity {

    private ActivityMainBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        binding = ActivityMainBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());

        BottomNavigationView navView = findViewById(R.id.nav_view);
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        //获取App bar配置:AppBarConfiguration
        AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(
                R.id.navigation_home, R.id.navigation_dashboard, R.id.navigation_notifications)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_activity_main);
        //将NavController和AppBarConfiguration进行绑定
        NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
        //将需要交互的App barUI与NavController和AppBarConfiguration进行绑定
        NavigationUI.setupWithNavController(binding.navView, navController);
    }

}
  • navigation pop 和 push的时候 对Fragment的 操作是 replace,所以会导致生命周期重新走一遍

  • 其实Navigation使用很简单,navigation和activity(确切的说是Fragment)绑定之后,使用两个方法就行,一个是navigate,就是跳转,一个是navigateUp,就是返回。

如果想要跳转到新页面时,在Fragment中使用:

NavHostFragment.findNavController(this).navigate(destinationID, bundle);
NavHostFragment.findNavController(this).navigateUp();

布局:


<androidx.constraintlayout.widget.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingTop="?attr/actionBarSize">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav_view"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginEnd="0dp"
        android:background="?android:attr/windowBackground"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/bottom_nav_menu" />

    <fragment
        android:id="@+id/nav_host_fragment_activity_main"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@id/nav_view"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/mobile_navigation" />

androidx.constraintlayout.widget.ConstraintLayout>

NavHostFragment:

android:name="androidx.navigation.fragment.NavHostFragment"

这句话是在告诉系统,这是一个特殊的Fragment 。

app:defaultNavHost=“true”:

app:defaultNavHost="true"

将defaultNavHost属性设置为true,则该Fragment会自动处理系统返回键,即,当用户按下手机的返回按钮时,系统能自动将当前的Fragment推出。

app:navGraph=“@navigation/nav_graph”:

app:navGraph="@navigation/nav_graph"

设置该Fragment对应的导航图 。

导航图文件 :@navigation/mobile_navigation

<?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/mobile_navigation"
    app:startDestination="@+id/navigation_home">

    <fragment
        android:id="@+id/navigation_home"
        android:name="com.xq.mybottomnavigation.ui.home.HomeFragment"
        android:label="@string/title_home"
        tools:layout="@layout/fragment_home" />

    <fragment
        android:id="@+id/navigation_dashboard"
        android:name="com.xq.mybottomnavigation.ui.dashboard.DashboardFragment"
        android:label="@string/title_dashboard"
        tools:layout="@layout/fragment_dashboard" />

    <fragment
        android:id="@+id/navigation_notifications"
        android:name="com.xq.mybottomnavigation.ui.notifications.NotificationsFragment"
        android:label="@string/title_notifications"
        tools:layout="@layout/fragment_notifications" />
</navigation>

fragment

三个fragment类似

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;

import com.xq.mybottomnavigation.R;
import com.xq.mybottomnavigation.databinding.FragmentHomeBinding;

public class HomeFragment extends Fragment {

    private HomeViewModel homeViewModel;
    private FragmentHomeBinding binding;

    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        homeViewModel =
                new ViewModelProvider(this).get(HomeViewModel.class);

        binding = FragmentHomeBinding.inflate(inflater, container, false);
        View root = binding.getRoot();

        final TextView textView = binding.textHome;
        homeViewModel.getText().observe(getViewLifecycleOwner(), new Observer<String>() {
            @Override
            public void onChanged(@Nullable String s) {
                textView.setText(s);
            }
        });
        return root;
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        binding = null;
    }

}

<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=".ui.home.HomeFragment">

    <TextView
        android:id="@+id/text_home"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:textAlignment="center"
        android:textSize="20sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
androidx.constraintlayout.widget.ConstraintLayout>

其他

Activity中导航到指定fragment

//方式一 、 通过NavController
NavController controller = Navigation
        .findNavController(this, R.id.nav_host_fragment_activity_main);
binding.btn1.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        controller.navigate(R.id.navigation_notifications);
    }
});



//方式二 、 通过NavHostFragment
NavHostFragment fragment = (NavHostFragment) getSupportFragmentManager()
        .findFragmentById(R.id.nav_host_fragment_activity_main);
binding.btn2.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        if (fragment != null) {
            NavHostFragment.findNavController(fragment)
                    .navigate(R.id.navigation_notifications);
        }
    }
});

NotificationsFragment 返回上一级

textView.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        NavHostFragment.findNavController(NotificationsFragment.this).navigateUp();
    }
});

动态设置 navGraph,传参数

MainActivity : 发送数据

NavController controller = Navigation
        .findNavController(this, R.id.nav_host_fragment_activity_main);
NavInflater navInflater = controller.getNavInflater();
NavGraph navGraph = navInflater.inflate(R.navigation.mobile_navigation);
navGraph.setStartDestination(R.id.navigation_notifications);//初始界面

Bundle args = new Bundle();
args.putBoolean("6no6", true);//传参

navController.setGraph(navGraph, args);

或者

//动态加载setGraph
FragmentManager manager = getSupportFragmentManager();
NavHostFragment hostFragment = (NavHostFragment) manager
        .findFragmentById(R.id.nav_host_fragment_activity_main);
NavController controller = null;
if (hostFragment != null) {
    controller = hostFragment.getNavController();
}
navController.setGraph(R.navigation.mobile_navigation);

NotificationsFragment : 接收数据

Bundle arguments = getArguments();
if (arguments != null) {
    boolean aBoolean = arguments.getBoolean("6no6");
    textView.setTextColor(aBoolean ? Color.RED : Color.BLUE);
}

导航监听:

navController.addOnDestinationChangedListener(new NavController.OnDestinationChangedListener() {
    @Override
    public void onDestinationChanged(@NonNull @NotNull NavController controller,
                                     @NonNull @NotNull NavDestination destination,
                                     @Nullable Bundle arguments) {
        CharSequence label = destination.getLabel();
        Log.e(TAG, "onDestinationChanged: ===="+label);
    }
});

切换时使Fragment保存状态

在进行跳转时 直接使用了replace,所以导致当前页面会调用 onDestroyView,即fragment变为 inactive,当进行pop操作时,fragment重新进入 active状态时,会重新调用 onViewCreated 等方法,导致页面重新绘制,
其实在这种情况下,我们可以直接用ViewModelLiveData对数据进行保存,但是这次想尝试一下新的解决办法。
在知道原因后就好办了,直接继承FragmentNavigator把方法重写

public NavDestination navigate(@NonNull Destination destination, @Nullable Bundle args,
            @Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {
        
//      ft.replace(mContainerId, frag);

//      change to  

        if(mFragmentManager.getFragments().size()>0){
            ft.hide(mFragmentManager.getFragments().get(mFragmentManager.getFragments().size()-1));
            ft.add(mContainerId, frag);
        }else {
            ft.replace(mContainerId, frag);
        }
        
}

KeepStateFragmentNavigator 使用如下:

NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
Fragment navHostFragment = getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment);
navController.getNavigatorProvider()
    .addNavigator(new KeepStateFragmentNavigator(this, 
                                    navHostFragment.getChildFragmentManager(), 
                                    R.id.nav_host_fragment));
NavHostFragment.findNavController(this).navigate(destinationID, bundle);

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