Android Studio 适配器和 Firebase

Question

当我在 Firebase 中删除某些内容时，为什么我的应用会崩溃？这是我的适配器

public class PostAdapter extends RecyclerView.Adapter<PostAdapter.ViewHolder> {

public Context mContext;
public List<Model> mPost;
private FirebaseStorage storage;
private FirebaseUser firebaseUser;
private StorageReference storageReference;
private ProgressDialog progressdialog;

public PostAdapter(Context mContext, List<Model> mPost) {
    this.mContext = mContext;
    this.mPost = mPost;
}

@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(mContext).inflate(R.layout.row, parent, false);
    return new PostAdapter.ViewHolder(view);
}

@Override
public void onDetachedFromRecyclerView(@NonNull RecyclerView recyclerView) {
    super.onDetachedFromRecyclerView(recyclerView);
}

@Override
public void onBindViewHolder(@NonNull final ViewHolder holder, int position) {

    firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
    final Model model = mPost.get(position);
     holder.postname.setText(model.getPetname());
    holder.postbreed.setText("Breed: " + model.getBreed());
    holder.postage.setText("Age: " + model.getAge());
    holder.postsize.setText("Size: " + model.getPetsize());
    holder.postcolor.setText("Color: " + model.getPetcolor());
    holder.postreason.setText(model.getReason());
    holder.postdate.setText(model.getPostdate());
    ownerinfo(holder.postby, holder.posterimage, model.getUserid());
    Glide.with(mContext.getApplicationContext()).load(model.getPetpicture()).into(holder.postimage);

    settinginfo(holder.settings,firebaseUser.getUid(),model.getUserid(),model.getPostid(),model.getBelong(),position);  


    isLike(model.getPostid(), holder.like);
    numberLkes(holder.likes, model.getPostid());
    getComments(model.getPostid(), holder.comments);



    holder.postby.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(mContext, OtherUserProfile.class);
            intent.putExtra("userid", model.getUserid());
            mContext.startActivity(intent);
        }
    });

    holder.posterimage.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(mContext, OtherUserProfile.class);
            intent.putExtra("userid", model.getUserid());
            mContext.startActivity(intent);
        }
    });


    holder.like.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (holder.like.getTag().equals("like")) {

                FirebaseDatabase.getInstance().getReference().child("Likes").child(model.getPostid()).child(firebaseUser.getUid()).setValue(true);
            } else {
                FirebaseDatabase.getInstance().getReference().child("Likes").child(model.getPostid()).child(firebaseUser.getUid()).removeValue();
            }
        }
    });

    holder.comment.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(mContext, CommentsSection.class);
            intent.putExtra("postid", model.getPostid());
            intent.putExtra("userid", model.getUserid());
            mContext.startActivity(intent);
        }
    });

    holder.comments.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(mContext, CommentsSection.class);
            intent.putExtra("postid", model.getPostid());
            intent.putExtra("userid", model.getUserid());
            mContext.startActivity(intent);
        }
    });


}

@Override
public int getItemCount() {
    return mPost.size();
}

public class ViewHolder extends RecyclerView.ViewHolder {

    public CircleImageView posterimage;
    public ImageView postimage, like, comment, settings;
    public Button adoptnme;
    public TextView postby, postname, postbreed, postage, postsize, postcolor, postreason, likes, postdate, comments;

    public ViewHolder(View itemView) {
        super(itemView);


        comments = itemView.findViewById(R.id.comments);
        comment = itemView.findViewById(R.id.comment);
        posterimage = itemView.findViewById(R.id.posterimage);
        postby = itemView.findViewById(R.id.postby);
        postdate = itemView.findViewById(R.id.postdate);
        postimage = itemView.findViewById(R.id.postimage);
        like = itemView.findViewById(R.id.like);
        likes = itemView.findViewById(R.id.likes);
        postname = itemView.findViewById(R.id.postname);
        postbreed = itemView.findViewById(R.id.postbreed);
        postage = itemView.findViewById(R.id.postage);
        postsize = itemView.findViewById(R.id.postsize);
        postcolor = itemView.findViewById(R.id.postcolor);
        postreason = itemView.findViewById(R.id.postreason);
        settings = itemView.findViewById(R.id.postsetting);


    }

}

private void getComments(String postid, final TextView comments) {
    DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Comments").child(postid);
    reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            comments.setText("View all " + dataSnapshot.getChildrenCount() + " comments");
        }

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

        }
    });
}

private void isLike(String postid, final ImageView imageView) {
    final FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
    DatabaseReference reference = FirebaseDatabase.getInstance().getReference()
            .child("Likes").child(postid);

    reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            if (dataSnapshot.child(firebaseUser.getUid()).exists()) {
                imageView.setImageResource(R.drawable.like);
                imageView.setTag("liked");

            } else {
                imageView.setImageResource(R.drawable.ic_favorite_border_black_24dp);
                imageView.setTag("like");
            }
        }

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

        }
    });
}

private void numberLkes(final TextView likes, String postid) {
    DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Likes").child(postid);
    reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            if (dataSnapshot.getChildrenCount() == 1 || dataSnapshot.getChildrenCount() == 0) {
                likes.setText(dataSnapshot.getChildrenCount() + " Like");
            } else {
                likes.setText(dataSnapshot.getChildrenCount() + " Likes");
            }
        }

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

        }
    });
}

private void ownerinfo(final TextView postby,
                       final CircleImageView posterimage,
                       String userid) {
    DatabaseReference reference = FirebaseDatabase.getInstance()
            .getReference("User").child(userid);
    reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            UserAdapter userAdapter = dataSnapshot.getValue(UserAdapter.class);
            Glide.with(mContext.getApplicationContext()).load(userAdapter.getProfilepic()).into(posterimage);
            //  Glide.with(mContext.getApplicationContext()) .using(new FirebaseImageLoader()) .load(storageReference) .signature(new StringSignature(uri.toString())) .diskCacheStrategy(DiskCacheStrategy.ALL) .placeholder(placeHolder) .into(imageView);
            postby.setText(userAdapter.getName());
        }


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

        }
    });


}

private void settinginfo(final ImageView setting, final String userid, final String poserid, final String postid, final String pettype, final int position) {

    setting.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (poserid.equals(userid)) {
                PopupMenu popupMenu = new PopupMenu(mContext, setting);
                popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                    public boolean onMenuItemClick(MenuItem item) {

                        switch (item.getItemId()) {
                            case R.id.editPost:
                                // item two clicked
                                return true;
                            case R.id.deletePost:
                                AlertDialog alertDialog = new AlertDialog.Builder(mContext)
                                        //set icon

                                        //set title
                                        .setTitle("Confirmation of deletion")
                                        //set message
                                        .setMessage("Delete this post?")
                                        //set positive button
                                        .setPositiveButton("Delete", new DialogInterface.OnClickListener() {
                                            @Override
                                            public void onClick(DialogInterface dialogInterface, int i) {
                                                progressdialog = new ProgressDialog(mContext);
                                                progressdialog.setMessage("Deleting...");
                                                progressdialog.show();
                                                FirebaseDatabase.getInstance().getReference().child("Likes").child(postid).removeValue();
                                                FirebaseDatabase.getInstance().getReference().child("Comments").child(postid).removeValue();
                                                String storageUrl = pettype+"/"+postid;
                                                StorageReference storageReference = FirebaseStorage.getInstance().getReference().child(storageUrl);
                                                FirebaseDatabase.getInstance().getReference(pettype).child(postid).removeValue();
                                                storageReference.delete().addOnSuccessListener(new OnSuccessListener<Void>() {
                                                    @Override
                                                    public void onSuccess(Void aVoid) {
                                                        progressdialog.dismiss();
                                                        Toast.makeText(mContext, "Post has has been deleted",Toast.LENGTH_LONG).show();




                                                    }
                                                });





                                            }
                                        })
                                        //set negative button
                                        .setNegativeButton("Dont delete", new DialogInterface.OnClickListener() {
                                            @Override
                                            public void onClick(DialogInterface dialogInterface, int i) {
                                                //set what should happen when negative button is clicked

                                            }
                                        })
                                        .show();
                                return true;
                        }

                        return false;
                    }
                });
                popupMenu.inflate(R.menu.setting_photo);
                popupMenu.show();

            }
            else
            {
                PopupMenu popupMenu = new PopupMenu(mContext, setting);
                popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                    public boolean onMenuItemClick(MenuItem item) {

                        switch (item.getItemId()) {
                            case R.id.reportPost:
                                // item two clicked
                                return true;
                        }

                        return false;
                    }
                });
                popupMenu.inflate(R.menu.report_photo);
                popupMenu.show();
            }
        }
    });

}
}

使用该适配器后它崩溃并出现错误

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.jasper.happy_paws.Model.getUserid()' on a null object reference
        at com.example.jasper.happy_paws.PostAdapter.onBindViewHolder(PostAdapter.java:71)
        at com.example.jasper.happy_paws.PostAdapter.onBindViewHolder(PostAdapter.java:40)

Answer 1

如果您想防止您的应用程序崩溃，这是一个快速的解决方案。这不是最好的解决方案，但这确实会阻止应用程序崩溃。

尝试/捕捉

在将数据设置到 View 中时，请确保在代码中使用 try/catch 语句来捕获空指针

正如您所说，根据您的日志，当您尝试使用方法 mode.getuserUid()(类似的方法)从模型中获取 uid 时，会出现一个空指针。

所以现在你将这部分绑定(bind)在 try/catch 中并捕获空指针(如果有的话)

try{
   //your code comes here like in your case you are grabbing so much data from model object
}catch(NullPointerException e){
   //here you can show the default data you want if there is no value deefined
}