在 Android Studio 中出现错误 - '无法为 child() 中的参数'pathString'传递 null

Question

我正在尝试从我的 Android 应用程序的实时数据库中获取

postid

。 但是，我无法这样做，并且在我的

isLiked()

函数中不断遇到错误：

Can't pass null for argument 'pathString' in child()

我的代码：

    package com.example.lively.Adapter;
    
    import android.content.Context;
    import android.content.Intent;
    import android.content.SharedPreferences;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ImageView;
    import android.widget.TextView;
    
    import androidx.annotation.NonNull;
    import androidx.fragment.app.FragmentActivity;
    import androidx.recyclerview.widget.RecyclerView;
    
    import com.bumptech.glide.Glide;
    import com.example.lively.CommentActivity;
    import com.example.lively.Model.Post;
    import com.example.lively.Model.User;
    import com.example.lively.PostDetailFragment;
    import com.example.lively.ProfileFragment;
    import com.example.lively.R;
    import com.google.firebase.auth.FirebaseAuth;
    import com.google.firebase.auth.FirebaseUser;
    import com.google.firebase.database.DataSnapshot;
    import com.google.firebase.database.DatabaseError;
    import com.google.firebase.database.DatabaseReference;
    import com.google.firebase.database.FirebaseDatabase;
    import com.google.firebase.database.ValueEventListener;
    
    import java.util.List;
    
    public class PostAdapter extends RecyclerView.Adapter<PostAdapter.ViewHolder> {
        public Context mContext;
        public List<Post> mPost;
    
        private FirebaseUser firebaseUser;
    
        public PostAdapter(Context mContext, List<Post> mPost) {
            this.mContext = mContext;
            this.mPost = mPost;
        }
    
        @NonNull
        @Override
        public PostAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(mContext).inflate(R.layout.post_items, parent, false);
            return new ViewHolder(view);
        }
    
        @Override
        public void onBindViewHolder(@NonNull PostAdapter.ViewHolder holder, int position) {
            firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
            Post post = mPost.get(position);
    
            Glide.with(mContext).load(post.getPostImage()).into(holder.postImage);
    
            if (post.getDescription().equals("")) {
                holder.description.setVisibility(View.GONE);
            } else {
                holder.description.setVisibility(View.VISIBLE);
                holder.description.setText(post.getDescription());
            }
    
            publisherInfo(holder.profileImage, holder.username, holder.publisher, post.getPublisher());
            if(post.getPostId()!=null)
                isLiked(post.getPostId(), holder.like);
            nrLikes(holder.likes, post.getPostId());
            getComments(post.getPostId(), holder.comments);
            isSaved(post.getPostId(), holder.save);
    
            holder.profileImage.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    SharedPreferences.Editor editor = mContext.getSharedPreferences("PEEFS", Context.MODE_PRIVATE).edit();
                    editor.putString("profileid", post.getPublisher());
    
                    ((FragmentActivity)mContext).getSupportFragmentManager().beginTransaction().replace(R.id.frameLayout, new ProfileFragment()).commit();
    
                }
            });
    
            holder.username.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    SharedPreferences.Editor editor = mContext.getSharedPreferences("PEEFS", Context.MODE_PRIVATE).edit();
                    editor.putString("profileid", post.getPublisher());
    
                    ((FragmentActivity)mContext).getSupportFragmentManager().beginTransaction().replace(R.id.frameLayout, new ProfileFragment()).commit();
    
                }
            });
            holder.publisher.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    SharedPreferences.Editor editor = mContext.getSharedPreferences("PEEFS", Context.MODE_PRIVATE).edit();
                    editor.putString("profileid", post.getPublisher());
    
                    ((FragmentActivity)mContext).getSupportFragmentManager().beginTransaction().replace(R.id.frameLayout, new ProfileFragment()).commit();
    
                }
            });
    
            holder.postImage.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    SharedPreferences.Editor editor = mContext.getSharedPreferences("PEEFS", Context.MODE_PRIVATE).edit();
                    editor.putString("postid", post.getPostId());
    
                    ((FragmentActivity)mContext).getSupportFragmentManager().beginTransaction().replace(R.id.frameLayout, new PostDetailFragment()).commit();
    
                }
            });
    
            holder.save.setOnClickListener(v -> {
                if (holder.like.getTag().equals("save")) {
                    FirebaseDatabase.getInstance().getReference().child("Saves").child(firebaseUser.getUid())
                            .child(post.getPostId()).setValue(true);
                } else {
                    FirebaseDatabase.getInstance().getReference().child("Saves").child(firebaseUser.getUid())
                            .child(post.getPostId()).removeValue();
                }
            });
    
            holder.like.setOnClickListener(v -> {
                if (holder.like.getTag().equals("like")) {
                    FirebaseDatabase.getInstance().getReference().child("Likes").child(post.getPostId())
                            .child(firebaseUser.getUid()).setValue(true);
                } else {
                    FirebaseDatabase.getInstance().getReference().child("Likes").child(post.getPostId())
                            .child(firebaseUser.getUid()).removeValue();
                }
            });
    
            holder.comment.setOnClickListener(v -> {
                Intent intent = new Intent(mContext, CommentActivity.class);
                intent.putExtra("postid", post.getPostId());
                intent.putExtra("publisherid", post.getPublisher());
                mContext.startActivity(intent);
            });
    
            holder.comments.setOnClickListener(v -> {
                Intent intent = new Intent(mContext, CommentActivity.class);
                intent.putExtra("postid", post.getPostId());
                intent.putExtra("publisherid", post.getPublisher());
                mContext.startActivity(intent);
            });
    
        }
    
        @Override
        public int getItemCount() {
            return mPost.size();
        }
    
        public static class ViewHolder extends RecyclerView.ViewHolder {
            public ImageView profileImage, postImage, like, comment, save;
            public TextView username, likes, publisher, description, comments;
    
            public ViewHolder(@NonNull View itemView) {
                super(itemView);
    
                profileImage = itemView.findViewById(R.id.imageProfile);
                postImage = itemView.findViewById(R.id.postImage);
                like = itemView.findViewById(R.id.like);
                comment = itemView.findViewById(R.id.comment);
                save = itemView.findViewById(R.id.save);
                username = itemView.findViewById(R.id.username);
                likes = itemView.findViewById(R.id.likes);
                publisher = itemView.findViewById(R.id.publisher);
                description = itemView.findViewById(R.id.description);
                comments = itemView.findViewById(R.id.comments);
            }
        }
    
        private void getComments(String postid, TextView comments) {
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Comments").child(postid);
            reference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot snapshot) {
                    comments.setText("View all " + snapshot.getChildrenCount() + " comments");
                }
    
                @Override
                public void onCancelled(@NonNull DatabaseError error) {
    
                }
            });
    
        }
    
        private void isLiked(String postid, final ImageView imageView) {
            final FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
    
            if (firebaseUser != null ) {
                DatabaseReference reference = FirebaseDatabase.getInstance().getReference()
                        .child("Likes")
                        .child(postid);
    
                reference.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot snapshot) {
                        if (snapshot.child(firebaseUser.getUid()).exists()) {
                            imageView.setImageResource(R.drawable.baseline_thumb_up_alt_24);
                            imageView.setTag("liked");
                        } else {
                            imageView.setImageResource(R.drawable.baseline_thumb_up_off_alt_24);
                            imageView.setTag("like");
                        }
                    }
    
                    @Override
                    public void onCancelled(@NonNull DatabaseError error) {
    
                    }
                });
            }
        }
    
    
        private void nrLikes(final TextView likes, String postid) {
            DatabaseReference reference1 = FirebaseDatabase.getInstance().getReference().child("Likes")
                    .child(postid);
            reference1.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot snapshot) {
                    likes.setText(snapshot.getChildrenCount() + "likes");
                }
    
                @Override
                public void onCancelled(@NonNull DatabaseError error) {
    
                }
            });
        }
    
        private void publisherInfo(ImageView imageProfile, TextView username, TextView publisher, String userid) {
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users").child(userid);
    
            reference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot snapshot) {
                    User user = snapshot.getValue(User.class);
                    Glide.with(mContext).load(user.getImageurl()).into(imageProfile);
                    username.setText(user.getUsername());
                    publisher.setText(user.getUsername());
                }
    
                @Override
                public void onCancelled(@NonNull DatabaseError error) {
    
                }
            });
    
        }
    
        private void isSaved(final String postid, ImageView imageView) {
            FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
    
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Saves")
                    .child(firebaseUser.getUid());
    
            reference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot snapshot) {
                    if (snapshot.child(postid).exists()) {
                        imageView.setImageResource(R.drawable.baseline_bookmark_24);
                        imageView.setTag("saved");
                    } else {
                        imageView.setImageResource(R.drawable.round_bookmark_border_24);
                        imageView.setTag("save");
                    }
                }
    
                @Override
                public void onCancelled(@NonNull DatabaseError error) {
    
                }
            });
    
        }
    }

实时数据库如下所示：

我尝试用不同的 if-else 条件来绑定孩子，但它不起作用。正如我们从上面的代码中看到的，我试图在进入 isLiked 函数之前进行检查。尽管如此，我还是没有看到任何进展。

Answer 1

正如 @TamasCsizmadia 最初在您的代码中发现的那样，当您使用时：

if (post.getPostId()!=null);
//                        👆

行尾有分号，表示这行代码后面的所有内容都不属于 if 语句范围。

根据之前的评论，您说您已经删除了行尾的分号，但您得到了相同的错误。查看您的代码可以确认该行为。为什么？这是因为您没有使用大括号

{}

，这基本上意味着只有下一行被评估为 if 语句的一部分：

if(post.getPostId()!=null)
    isLiked(post.getPostId(), holder.like);
//👆
nrLikes(holder.likes, post.getPostId());
getComments(post.getPostId(), holder.comments);
isSaved(post.getPostId(), holder.save);

IDE 中的缩进也表明了这一点。要解决此问题，请使用如下所示的花括号：

if(post.getPostId()!=null) {
    isLiked(post.getPostId(), holder.like);
    nrLikes(holder.likes, post.getPostId());
    getComments(post.getPostId(), holder.comments);
    isSaved(post.getPostId(), holder.save);
}

现在所有四行代码都是 if 语句范围的一部分。