将底部导航栏视图实现到一个片段中

Question

在我的Android Studio项目中，我想在MainActivity中实现一个带有片段和底部导航视图的NavigationDrawer。

以下是一个片段的代码：

public class U16 extends Fragment{

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    getActivity().setTitle("TITOLO U16");
}

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

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

        switch (item.getItemId()) {
            case R.id.navigation_home:
                fragmentTransaction.replace(R.id.content, new Calendario()).commit();
                return true;
            case R.id.navigation_dashboard:
                fragmentTransaction.replace(R.id.content, new Palestre()).commit();
                return true;
            case R.id.navigation_notifications:
                fragmentTransaction.replace(R.id.content, new Squadra()).commit();
                return true;
        }
        return false;
    }

};

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

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

    FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.content, new Calendario()).commit();

    return inflater.inflate(R.layout.u16_layout, container, false);
}

我遇到了这个错误：

FATAL EXCEPTION: main
Process: app.navigationdrawerfragment, PID: 21499
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.BottomNavigationView.setOnNavigationItemSelectedListener(android.support.design.widget.BottomNavigationView$OnNavigationItemSelectedListener)' on a null object reference at app.navigationdrawerfragment.U16.onCreateView(U16.java:52)

我知道这个错误在"OnCreateView"过程中出现，是因为执行了"navigation.setOnNavigationItemSelectedListener..."。这是u16_layout.xml的内容：

<?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="simone.biliato.navigationdrawerfragment.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" />

</LinearLayout>

那么，有人尝试过做同样的事情吗？

- Simone

---

你能在这里发布与此“Fragment”相关的“Activity”布局吗？ - Giorgio Antonioli

嗨，Fondesa。我已经编辑了第一个问题的布局。 - Simone

有人可以帮帮我吗？拜托了 :( - Simone

Answer 1

您正在尝试设置未创建的对象。将代码移动到onViewCreated事件中，如下所示：

     @Override
        public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
            super.onViewCreated(view, savedInstanceState);
            getActivity().setTitle("Titolo");

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

    FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.content, new Calendario()).commit();

    return inflater.inflate(R.layout.u16_layout, container, false);
        }

这将会起作用 :)

- img.simone