在BottomNavigationView中开始片段

Question

我正在使用带有底部导航视图的简单应用程序。我有3个带有文本的片段，我想在Botton
Navigation中选择一个项目时启动它们，但是我不知道在MainActivity.java中写什么。所有片段都具有.xml布局和.java。我搜索了一些代码，写了代码，搜索了视频，但没有成功。

我正在学习Fragments和UI Dynamic，因此我在Android
Studio中使用“底部导航活动”创建了一个新项目。因此，在我的activity_main中，我在“底部导航”中有3个iten，在“底部导航”之上有一个framelayout，并占用了所有父对象。这个想法是：当我在“底部导航”中选择一个项目时，它将在框架布局中显示另一个布局。所以我在布局文件夹中创建了3个xml布局（也带有java类），在framelayout中创建了一个片段。现在，当我选择一个项目时，我试图在我的framelayout（有一个片段）中显示这些布局。但是我不知道该怎么做。

主要活动

private TextView mTextMessage;

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
        = new BottomNavigationView.OnNavigationItemSelectedListener() {

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        Fragment selectedFragment = null;
        switch (item.getItemId()) {
            case R.id.navigation_home:
                selectedFragment = HomeFragment.newInstance();
                break;
            case R.id.navigation_dashboard:
                selectedFragment = DashboardFragment.newInstance();
                break;
            case R.id.navigation_notifications:
                selectedFragment = NotificationsFragment.newInstance();
                break;
        }
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.replace(R.id.content, selectedFragment);
        transaction.commit();
        return true;
    }

};

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


    BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
    navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);

    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.replace(R.id.content, HomeFragment.newInstance());
    transaction.commit();
}

activity_main xml

<LinearLayout
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"
android:orientation="vertical"
tools:context="bandeira.thalisson.barradenavegacaoembaixo.MainActivity">

<FrameLayout
    android:id="@+id/content"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1">
</FrameLayout>

<android.support.design.widget.BottomNavigationView
    android:id="@+id/navigation"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom"
    android:background="?android:attr/windowBackground"
    app:menu="@menu/navigation"/>

导航xml

<item
    android:id="@+id/Fragment_one"
    android:icon="@drawable/ic_home_black_24dp"
    android:title="@string/title_home"/>

<item
    android:id="@+id/Fragment_two"
    android:icon="@drawable/ic_dashboard_black_24dp"
    android:title="@string/title_dashboard"/>

<item
    android:id="@+id/Fragment_three"
    android:icon="@drawable/ic_notifications_black_24dp"
    android:title="@string/title_notifications"/>

Fragment.java示例

public class HomeFragment extends Fragment {

public static HomeFragment newInstance() {
    HomeFragment fragment = new HomeFragment();
    return fragment;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.navigation_home, container, false);
    return inflater.inflate(R.layout.navigation_home, container, false);
}

Answer 1

首先，在您的activity_main.xml中，我们不需要3个不同的片段，因为我们只能在1个FrameLayout中替换或添加任何选定的片段。其次，只要用户从Bottom
NavigationView中选择任何一个，就只需获取相关Fragment类的实例，并将其替换为activity_main的FrameLayout即可。

Fragment selectedFragment = null;
         switch (item.getItemId()) {
               case R.id.navigation_home:
                   selectedFragment = FunFragment.newInstance();
                   break;

在获得选定片段的实例后，将其替换为activity_main的FrameLayout，以显示在屏幕上。

FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
            transaction.replace(R.id.content, selectedFragment);
            transaction.commit();

编辑标记 步骤1. 您的activity_main.xml应该如下所示

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    tools:context="com.exampl.MainActivity">
    <FrameLayout
        android:id="@+id/content"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"/>
    <android.support.design.widget.BottomNavigationView
        android:id="@+id/navigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"
        android:background="?android:attr/windowBackground"
        app:menu="@menu/navigation" />
</LinearLayout>

步骤2. 您的fragment_home.xml布局应如下所示

 <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical" android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="android"/>
    </LinearLayout>

为您的三个不同选项制作3种不同的片段布局

步骤3. 您的MainActivity.java类将如下所示

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
                = new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(MenuItem item) {
                Fragment selectedFragment = null;
                switch (item.getItemId()) {
                    case R.id.navigation_home:
                        selectedFragment = FunFragment.newInstance();
                       break;
                    case R.id.navigation_dashboard:
                        selectedFragment = TheoryFragment.newInstance();
                       break;
                    case R.id.navigation_notifications:
                        selectedFragment = AndroidFragment.newInstance();
                        break;
                }
                FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
                transaction.replace(R.id.content, selectedFragment);
                transaction.commit();
                return true;
            }
        };

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.bind(this);

        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);

        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.replace(R.id.content, FunFragment.newInstance());
        transaction.commit();
    }

在on create上替换为要在启动应用程序后显示的片段，导航监听器将照顾您将选择的任何选项

步骤4. 您将拥有3个不同的Fragment类，如下所示

public class TheoryFragment extends Fragment {

     public static TheoryFragment newInstance() {
            TheoryFragment fragment = new TheoryFragment();
            return fragment;
        }
     @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_theory, container, false);
            unbinder = ButterKnife.bind(this, rootView);
            return rootView;
        }
    }

希望它能对您有所帮助，如有任何问题，请告诉我。