一个巧妙的方法获取 fragment 的 NavController

同时Activity的左上角ActionBar 有个回退的箭头。非常简单的代码，就能实现了无限切换fragment的布局，不管你有多少个fragment 都能随时切换，完全可以用来单个Activity ,多个 fragment架构APP。以下是Test6_Activity,就是一个 viewpager2，以及Mobile_Fragment 的生命周期监控回调，就是为了在 onResume 的时候取

android源码

639人浏览 · 2023-07-05 07:21:47

android源码 · 2023-07-05 07:21:47 发布

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viewpager2 中的 fragment 嵌套使用 androidx.navigation.fragment.NavHostFragment
ViewPager2 基础的就不赘述了。
下面这是mobile_fragment 的布局：

<?xml version="1.0" encoding="utf-8"?>
<layout 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">

    <data>

    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="dialog"
            android:textSize="30sp" />

        <fragment
            android:id="@+id/nav_host_fragment_fragment_test6_dialog"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:defaultNavHost="true" />  //注意，不直接设置 setGraph ,放在 java代码中设置，方便灵活切换 Navigation
    </LinearLayout>
</layout>

下面是Mobile_Fragment :

public class Mobile_Fragment extends BaseFragment<MobileFragmentBinding> {
    @Override
    protected int getLayoutId() {
        return R.layout.mobile_fragment;
    }

    @Override
    protected void initView() {
        Loge.e(this.toString());

    }

    @Override
    public void onAttach(@NonNull Context context) {
        super.onAttach(context);
        Test6_Activity test6_activity = (Test6_Activity) context;
        getLifecycle().addObserver(test6_activity.new FragmentLifecycle());//监控fragment生命周期
    }

    @Override
    public void onResume() {
        super.onResume();
    initNav(1);//这里灵活设置 setGraph 方便随时切换 navigation文件，复制布局也可以简单灵活设置。
    }
 private void initNav(int type) {
        NavController controller = Navigation.findNavController(this, R.id.nav_host_fragment_fragment_test6_dialog); //在Activity里获取NavController实例
        if (type == 1) {
            controller.setGraph(R.navigation.fragment7);  //设置xml文件
            return;
        }
        if (type == 2) {
            Bundle bundle = new Bundle();
            bundle.putString("name", "demo");
            controller.setGraph(R.navigation.mobile_navigation); //设置xml文件的并传入数据，这个数据可以在启动的Fragment里获取到
            return;
        }
        if (type == 3) {
            controller.setGraph(R.navigation.navigation_dialog); //设置xml文件的并传入数据，这个数据可以在启动的Fragment里获取到
            return;
        }
        finish();
    }
    @Override
    protected void initData() {

    }
}

以下是 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"
    android:id="@+id/mobile_navigation"
    app:startDestination="@+id/navigation_home">

    <fragment
        android:id="@+id/navigation_home"
        android:name="com.android.test2mvvm.test4.ui.home.HomeFragment"
        android:label="@string/title_home"
        tools:layout="@layout/fragment_home" />

    <fragment
        android:id="@+id/navigation_dashboard"
        android:name="com.android.test2mvvm.test4.ui.dashboard.DashboardFragment"
        android:label="@string/title_dashboard"
        tools:layout="@layout/fragment_dashboard" />

    <fragment
        android:id="@+id/navigation_notifications"
        android:name="com.android.test2mvvm.test4.ui.notifications.NotificationsFragment"
        android:label="@string/title_notifications"
        tools:layout="@layout/fragment_notifications" />
</navigation>

以下是Test6_Activity,就是一个 viewpager2，以及Mobile_Fragment 的生命周期监控回调，就是为了在 onResume 的时候取到NavController (在其他生命周期取到的为null)

@Route(path = Constants.TEST6_ACTIVITY)
public class Test6_Activity extends BaseActivity<Test6_ViewModel, Test6ActivityBinding> {
    @Override
    protected int getContentViewId() {
        return R.layout.test6_activity;
    }

    @Override
    protected void processLogic() {
        ActionBar actionBar = getSupportActionBar();
        actionBar.setDisplayHomeAsUpEnabled(true);

        List<Fragment> fragmentList = new ArrayList<>();
        fragmentList.add(new Mobile_Fragment());
        fragmentList.add(new Dialog_Fragment());
        fragmentList.add(new Fragment07());
        MyViewPager2Adapter myViewPager2Adapter = new MyViewPager2Adapter(this, fragmentList);
        binding.viewpager2ActivityTest6.setAdapter(myViewPager2Adapter);

        new TabLayoutMediator(binding.tablayoutActivityTest6, binding.viewpager2ActivityTest6, new TabLayoutMediator.TabConfigurationStrategy() {
            @Override
            public void onConfigureTab(@NonNull TabLayout.Tab tab, int position) {
                tab.setText(fragmentList.get(position).toString());
            }
        }).attach();
    }

    NavController navController1;

    @Override
    public boolean onSupportNavigateUp() {
        if (navController1 != null) return navController1.navigateUp();
        return super.onSupportNavigateUp();
    }

 public class FragmentLifecycle implements DefaultLifecycleObserver {
        @Override
        public void onResume(@NonNull LifecycleOwner owner) {
            DefaultLifecycleObserver.super.onResume(owner);
            if (owner instanceof Dialog_Fragment) {
                Dialog_Fragment dialog_fragment = (Dialog_Fragment) owner;
               navController1= Navigation.findNavController(dialog_fragment.getView().findViewById(R.id.nav_host_fragment_fragment_test6_dialog));
            }
            if (owner instanceof Fragment07) {
                Fragment07 fragment07 = (Fragment07) owner;
                navController1 = Navigation.findNavController(fragment07.getView().findViewById(R.id.nav_host_fragment_fragment_test6_navigation));
            }
            if (owner instanceof Mobile_Fragment) {
                Mobile_Fragment mobile_fragment = (Mobile_Fragment) owner;
               navController1= Navigation.findNavController(mobile_fragment.getView().findViewById(R.id.nav_host_fragment_fragment_test6_mobile));
            }
            NavigationUI.setupActionBarWithNavController(Test6_Activity.this,navController1);
        }
    }
}

Test6_Activity 的布局:

<?xml version="1.0" encoding="utf-8"?>
<layout 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">

    <data>

    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:id="@+id/test6_activity_tv"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:text="test6_activity"
            android:textSize="30sp"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <fragment
            android:id="@+id/nav_host_fragment_activity_test6"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="1dp"
            app:defaultNavHost="true"
            app:layout_constraintTop_toBottomOf="@id/test6_activity_tv" />

        <com.google.android.material.tabs.TabLayout
            android:id="@+id/tablayout_activity_test6"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:layout_constraintTop_toBottomOf="@id/nav_host_fragment_activity_test6" />

        <androidx.viewpager2.widget.ViewPager2
            android:id="@+id/viewpager2_activity_test6"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            app:layout_constraintTop_toBottomOf="@id/tablayout_activity_test6"
            app:layout_constraintVertical_weight="1" />

    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

最终实现的效果就是,一个ViewPager2内有多个fragment,每个fragment 里面有个NavHostFragment容器，每个容器里面可以放多个fragment 互相跳转（使用Navigation）,而且可以随时切换Navigation。同时Activity的左上角ActionBar 有个回退的箭头。非常简单的代码，就能实现了无限切换fragment的布局，不管你有多少个fragment 都能随时切换，完全可以用来单个Activity ,多个 fragment 架构APP

抓了几张图，大家看效果：

在这里插入图片描述