java - 我得到 fragment id 无 View

Question

我正在尝试在我的 fragment 中进行 Activity ， fragment 显示您关注的人的帖子， Activity 显示任何人的最新帖子。

我的 fragment ..

 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 Activity ..

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) {
            }
        });
    }
}

我遇到致命异常:当我单击用户名转到他们的个人资料时，主应用程序和我的应用程序崩溃了。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

我可以看到，如果启用断言，您的代码中有一点将会崩溃:

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

您在那里写的内容相当于:

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

我确信您不想在没有帖子的情况下使整个应用程序崩溃？

如果您想测试它是否存在(如果不存在则获取反馈)，请尝试如下操作:

            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);
                }
            }

引用:

https://en.wikibooks.org/wiki/Java_Programming/Keywords/assert How to use assert in android?