android - 我正在尝试调用 DisplayMatch 给 listviewMatch.setAdapter(adapter) 中的错误，如果可能的话，请帮助我提供任何替代方案

Question

**bottom_nav_bar.xml**

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/white"
    android:id="@+id/fragment_container">


    <com.ismaeldivita.chipnavigation.ChipNavigationBar
        android:id="@+id/bottom_nav_menu"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:cnb_menuResource="@menu/bottom_nav_menu"
        android:layout_alignParentBottom="true"
        android:background="@drawable/round_corners"
        app:cnb_unselectedColor="@color/black"
        app:cnb_radius="8dp"
        app:cnb_orientationMode="horizontal"
        android:layout_margin="30dp"
        android:elevation="8dp"
        />


</RelativeLayout>


**list_view_data.xml**

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

    <ListView
        android:id="@+id/lst"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>


**match_view.xml**

<?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:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/black"
    android:orientation="vertical">

    <androidx.cardview.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        app:cardCornerRadius="5dp">


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


            <ImageView
                android:id="@+id/imageView2"
                android:layout_width="match_parent"
                android:layout_height="150dp"
                android:adjustViewBounds="true"
                android:scaleType="centerCrop"
                app:srcCompat="@drawable/pubg_test" />


        </LinearLayout>

    </androidx.cardview.widget.CardView>

</LinearLayout>

**bottom_nav_menu.xml**

    <?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <item
        android:id="@+id/bottom_nav_dashboard"
        android:title="Dashboard"
        android:icon="@drawable/bottom_nav_dashboard_icon"
        app:cnb_backgroundColor="#FFC107"
        />

    <item
        android:id="@+id/bottom_nav_manage"
        android:title="Manage"
        android:icon="@drawable/bottom_nav_manage_icon"
        app:cnb_backgroundColor="#FFC107"
        />

    <item
        android:id="@+id/bottom_nav_profile"
        android:title="Profile"
        android:icon="@drawable/bottom_nav_profile_icon"
        app:cnb_backgroundColor="#FFC107"
        />

</menu>






 




public class DashBoardTest extends AppCompatActivity {

    ChipNavigationBar chipNavigationBar;
    ListView listviewMatch;
    DatabaseReference displayMatch;
    List<MatchData> matchData;
    private Boolean ID=false;


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


        chipNavigationBar = findViewById(R.id.bottom_nav_menu);
        matchData = new ArrayList<>();
        displayMatch = FirebaseDatabase.getInstance().getReference("match");

        chipNavigationBar.setItemSelected(R.id.bottom_nav_manage, true);
        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, new UserTournment2()).commit();
        NavbottomMenu();
        if (!ID)
        {
            DisplayMatch();
        }



    }


    @SuppressLint("NonConstantResourceId")
    private void NavbottomMenu() {

        chipNavigationBar.setOnItemSelectedListener(i -> {
            Fragment fragment = null;
            switch (i) {
                case R.id.bottom_nav_dashboard:
                    fragment = new UserHome();
                    break;
                case R.id.bottom_nav_manage:
                    fragment = new UserTournment2();
                    break;
                case R.id.bottom_nav_profile:
                    fragment = new UserDetails();
                    break;
            }
            assert fragment != null;
            getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, fragment).commit();
        });

    }


    public void DisplayMatch() {

        listviewMatch = findViewById(R.id.lst);

        displayMatch.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                matchData.clear();

                for (DataSnapshot artistSnapshot : dataSnapshot.getChildren()) {
                    MatchData videos = artistSnapshot.getValue(MatchData.class);

                    matchData.add(videos);
                }
                MyListAdapter adapter = new MyListAdapter(DashBoardTest.thi`enter code here`s, matchData);
                listviewMatch.setAdapter(adapter);

                //retrive data
                //listviewMatch.setOnItemClickListener(this));

            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
                toastMessage("oncanelled");

            }
        });

    }

    public void toastMessage(String i) {

        Toast.makeText(this, i, Toast.LENGTH_SHORT).show();
    }


}

public class UserTournment2 extends Fragment   {



@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    Toast.makeText(getContext(), "fragment called", Toast.LENGTH_SHORT).show();
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.list_view_data, container, false);

}

}

public class MyListAdapter extends ArrayAdapter<MatchData> {




private  Activity context;
private List<MatchData> matchData;

public MyListAdapter(Activity context, List<MatchData> matchData) {
    super(context, R.layout.match_view, matchData);
    // TODO Auto-generated constructor stub

    this.context=context;
    this.matchData=matchData;

}

public View getView(int position, View view, ViewGroup parent) {
    LayoutInflater inflater=context.getLayoutInflater();
    View rowView=inflater.inflate(R.layout.match_view, null,true);

   
    return rowView;

};

}

public class MatchData {
String name, register_id, time, type;

public MatchData() {
}

public MatchData(String name, String register_id, String time, String type) {
    this.name = name;
    this.register_id = register_id;
    this.time = time;
    this.type = type;
}

public String getName() {
    return name;
}

public String getRegister_id() {
    return register_id;
}

public String getTime() {
    return time;
}

public String getType() {
    return type;
}

}

错误

2021-07-10 01:04:02.114 15625-15625/me.aksamitsah.pubgtest E/AndroidRuntime：致命异常：主进程：me.aksamitsah.pubgtest，PID：15625 java.lang.NullPointerException：尝试调用虚拟方法' void android.widget.ListView.setAdapter(android.widget.ListAdapter)' 在 com.google.firebase.database.core 的 me.aksamitsah.pubgtest.DashBoardTest$1.onDataChange(DashBoardTest.java:100) 的空对象引用上。 ValueEventRegistration.fireEvent(ValueEventRegistration.java:75) at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63) at com.google.firebase.database.core.view.EventRaiser$1.run (EventRaiser.java:55) 在 android.os.Handler.handleCallback(Handler.java:914) 在 android.os.Handler.dispatchMessage(Handler.java:100) 在 android.os.Looper.loop(Looper.java: 224) 在 android.app.ActivityThread.main(ActivityThread.java:7551) 在 java.lang.reflect.Method.invoke(Native Method) 在 com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539) 在 com.android.internal.os.ZygoteInit.main( ZygoteInit.java:995)

标签： androidfirebaseandroid-studio