我对片段的 id 没有视图

Question

我正在尝试在我的片段中添加一个活动，该片段显示您关注的人的帖子，该活动显示任何人的最新帖子。

我的片段..

 public class HomeFragment extends Fragment {

    private PostAdapter postAdapter;
    private List<Post> postLists;

    private List<String> followingList;

    private ProgressBar progressBar;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view=inflater.inflate(R.layout.fragment_home, container,false);

        RecyclerView recyclerView = view.findViewById(R.id.recycler_view);
        recyclerView.setHasFixedSize(true);
        LinearLayoutManager linearLayoutManager=new LinearLayoutManager(getContext());
        linearLayoutManager.setReverseLayout(true);
        linearLayoutManager.setStackFromEnd(true);
        recyclerView.setLayoutManager(linearLayoutManager);
        postLists=new ArrayList<>();
        postAdapter=new PostAdapter(getContext(), postLists);
        recyclerView.setAdapter(postAdapter);

        ImageView globalPosts = view.findViewById(R.id.globalPosts);

        globalPosts.setOnClickListener(v->{
            Intent intent= new Intent(getContext(), GlobalPostsActivity.class);
            startActivity(intent);
        });

        progressBar=view.findViewById(R.id.progress_circular);

        checkFollowing();

        return view;
    }

    private void checkFollowing(){
        followingList=new ArrayList<>();

        DatabaseReference reference=FirebaseDatabase.getInstance().getReference("Support")
                .child(Objects.requireNonNull(FirebaseAuth.getInstance().getCurrentUser()).getUid())
                .child("supporting");

        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                followingList.clear();
                for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                    followingList.add(snapshot.getKey());
                }
                readPosts();
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });
    }

    private void readPosts(){
        DatabaseReference reference= FirebaseDatabase.getInstance().getReference("Posts");
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                postLists.clear();
                for (DataSnapshot snapshot :dataSnapshot.getChildren()){
                    Post post=snapshot.getValue(Post.class);
                    for (String id: followingList){
                        assert post != null;
                        if (post.getPublisher().equals(id)){
                            postLists.add(post);
                        }
                    }
                }
                postAdapter.notifyDataSetChanged();
                progressBar.setVisibility(View.GONE);
            }
            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
            }
        });
    }
}

我的活动..

public class GlobalPostsActivity extends AppCompatActivity {

    private PostAdapter postAdapter;
    private List<Post> postLists;



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

        RecyclerView recyclerView = findViewById(R.id.recycler_view1);
        recyclerView.setHasFixedSize(true);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getApplicationContext());
        linearLayoutManager.setReverseLayout(true);
        linearLayoutManager.setStackFromEnd(true);
        recyclerView.setLayoutManager(linearLayoutManager);
        postLists=new ArrayList<>();
        postAdapter=new PostAdapter(this, postLists);
        recyclerView.setAdapter(postAdapter);

        readGlobalPosts();

    }
    private void readGlobalPosts(){
        DatabaseReference reference= FirebaseDatabase.getInstance().getReference("Posts");
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                postLists.clear();
                for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                    Post post=snapshot.getValue(Post.class);
                    assert post !=null;
                    postLists.add(post);
                }
                postAdapter.notifyDataSetChanged();
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
            }
        });
    }
}

我得到一个致命的异常：当我点击用户名进入他们的个人资料时，main 和我的应用程序崩溃。 我不确定为什么会发生这种情况，因此非常感谢任何帮助。

Answer 1

如果启用断言，我可以看到您的一小部分代码会崩溃：

            for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                Post post=snapshot.getValue(Post.class);
                assert post !=null; // THIS
                postLists.add(post);
            }

你在那里写的相当于：

            for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                Post post=snapshot.getValue(Post.class);
                if(post == null) {
                    throw new IllegalStateException("Post was null");
                }
                postLists.add(post);
            }

我确定您不想在没有 Post 的情况下使整个应用程序崩溃？

如果您想测试它是否存在（如果不存在则获得反馈），请尝试以下操作：

            for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                Post post=snapshot.getValue(Post.class);
                if(post == null) {
                    Log.w("TUT", "Expected a post and didn't get one.");
                } else {
                    postLists.add(post);
                }
            }

参考：

https://en.wikibooks.org/wiki/Java_Programming/Keywords/assert 如何在 android 中使用断言？