安卓无法转换java类型的值。util。HashMap到字符串，但代码中没有HashMap？

Question

我试图将添加到Firebase数据库的数据显示到安卓上。数据可以上传到数据库，但当我试图通过手机或模拟器显示数据时，会出现以下错误：

com.google.firebase.database.DatabaseException: Failed to convert value of type java.util.HashMap to String

在下列地点：

com.firebase.ui.database.FirebaseRecyclerAdapter.parseSnapshot(FirebaseRecyclerAdapter.java:147)

这是第146行和第147行的代码：

protected T parseSnapshot(DataSnapshot snapshot) {
    return snapshot.getValue(mModelClass);
}

此错误导致应用程序崩溃而无法运行。我相信这个错误是由于在我删除。应用程序将运行的子元素，但显然不会显示数据

mDatabase = FirebaseDatabase.getInstance().getReference().child("Blog");

我不确定为什么会抛出这个错误，因为我在数据库中仅有的数据类型是字符串，而且子“Blog”在我的数据库中拼写正确

另一条重要信息： 当我在firebase中删除“Blog”子项时，应用程序将运行。然而，一旦我向firebase提交数据，就会出现错误，我的应用程序就会崩溃

任何帮助都将不胜感激

此类显示以下数据：

public class MainActivity extends AppCompatActivity {

    private RecyclerView mPostList;
    private DatabaseReference mDatabase;

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

        mDatabase = FirebaseDatabase.getInstance().getReference().child("Blog");

        mPostList = (RecyclerView) findViewById(R.id.post_list);
        mPostList.setHasFixedSize(true);
        mPostList.setLayoutManager(new LinearLayoutManager(this));
    }

    @Override
    protected void onStart() {
        super.onStart();

        FirebaseRecyclerAdapter<Blog, BlogViewHolder> firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<Blog, BlogViewHolder>(
                Blog.class,
                R.layout.post_row,
                BlogViewHolder.class,
                mDatabase
                ) {
            @Override
            protected void populateViewHolder(BlogViewHolder viewHolder, Blog model, int position) {

                viewHolder.setTitle(model.getTitle());
                viewHolder.setDesc(model.getDesc());
                viewHolder.setImage(getApplicationContext(), model.getImage());
            }
        };

        mPostList.setAdapter(firebaseRecyclerAdapter);
    }

    public static class BlogViewHolder extends RecyclerView.ViewHolder {

        View mView;

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

            mView = itemView;
        }

        public void setTitle(String title) {
            TextView post_title = (TextView)mView.findViewById(R.id.post_title);
            post_title.setText(title);
        }

        public void setDesc(String desc) {
            TextView post_desc = (TextView)mView.findViewById(R.id.post_desc);
            post_desc.setText(desc);
        }

        public void setImage(Context ctx, String image) {
            ImageView post_image = (ImageView) mView.findViewById(R.id.post_image);
            Picasso.with(ctx).load(image).into(post_image);
        }
    }

    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main_menu, menu);
        return super.onCreateOptionsMenu(menu);
    }


    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        if (item.getItemId()== R.id.action_add){
            startActivity(new Intent(MainActivity.this, PostActivity.class));
        }

        return super.onOptionsItemSelected(item);
    }
}

此类将数据发布到firebase：

package infectionapp.com.infectionui;

public class PostActivity extends AppCompatActivity {

    private ImageButton mSelectImage;
    private Uri  mImageUri = null;
    private EditText mPostTitle;
    private EditText mPostDesc;
    private Button mSubmitBtn;

    private StorageReference mStorage;
    private DatabaseReference mDatabase;

   // private ProgressBar mProgress;
    private static final int GALLERY_REQUEST = 1;

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

        //Directs to root firebase storage
        mSelectImage = (ImageButton) findViewById(R.id.imageSelect);

        mStorage = FirebaseStorage.getInstance().getReference();
        mDatabase = FirebaseDatabase.getInstance().getReference().child("Blog");

        mPostTitle = (EditText) findViewById(R.id.titleField);
        mPostDesc = (EditText)findViewById(R.id.descField);
        mSubmitBtn = (Button) findViewById(R.id.submitBtn);

    //    mProgress = new ProgressBar(this);

        mSubmitBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startPosting();

            }
        });

        mSelectImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                Intent galleryIntent = new Intent(Intent.ACTION_GET_CONTENT);
                galleryIntent.setType("image/*");
                startActivityForResult(galleryIntent, GALLERY_REQUEST);
            }
        });
    }

    private void startPosting() {

       final String title_val = mPostTitle.getText().toString().trim();
       final String desc_val = mPostDesc.getText().toString().trim();

        if (!TextUtils.isEmpty(title_val) && !TextUtils.isEmpty(desc_val) && mImageUri != null){
                StorageReference filepath = mStorage.child("Post_Images").child(mImageUri.getLastPathSegment());

                filepath.putFile(mImageUri).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
                    @Override
                    public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {

                    Uri downloadUrl = taskSnapshot.getDownloadUrl();

                        //Creates unique ID for post
                        DatabaseReference newPost = mDatabase.push();
                        newPost.child("title").setValue(title_val);
                        newPost.child("desc").setValue(desc_val);
                        newPost.child("image").setValue(downloadUrl).toString();

                        startActivity(new Intent(PostActivity.this, MainActivity.class));
                    }
                });
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if(requestCode == GALLERY_REQUEST && resultCode == RESULT_OK){
            mImageUri = data.getData();
            mSelectImage.setImageURI(mImageUri);

        }
    }
}

Database structure:

Child nodes within children:

Code screenshot

Error of updated code

Answer 1

为了以最简单的方式获取数据，我建议您使用以下代码：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference blogRef = rootRef.child("Blog");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String desc = ds.child("desc").getValue(String.class);
            String title = ds.child("title").getValue(String.class);
            String image = ds.child("image").child("path").getValue(String.class);
            Log.d("TAG", desc + " / " + title + " / " + image);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
blogRef.addListenerForSingleValueEvent(eventListener);

您的输出将是：

tst / test / /v0/b/infectionui...

如你所见，我使用了字符串类。这也是你需要在^{中使用的

如果您想从图像中获取另一个值，只需与另一个子项更改.child("path")，比如.child("schemeSpecificPart")