从Firebase数据库获取数据时如何显示加载消息？

Question

我正在使用Firebase将数据显示到textview中。我使用asynctask在后台加载数据，而在加载时，我想在数据加载到textview中之前显示一条加载消息。

但是我的加载数据弹出窗口没有显示。（即doinBackground方法完成后，它可以立即工作），并且用户仅在Firebase数据加载之后才能看到空的文本视图。

如何防止这种情况并显示进程对话框，直到我的textview加载Firebase数据？

here is my code
<pre>
<code>
public class LastPage extends AppCompatActivity {
    TextView title, author, article;
    DatabaseReference mDatabase;

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


        title = (TextView) findViewById(R.id.last_page_title);
        author = (TextView) findViewById(R.id.last_page_author);
        article = (TextView) findViewById(R.id.last_page_article);

        mDatabase = FirebaseDatabase.getInstance().getReference();

        new LoadFirebaseData().execute();


    }

    private class LoadFirebaseData extends AsyncTask<Void, Void, Integer>
    {
        private ProgressDialog Dialog = new ProgressDialog(LastPage.this);

        @Override
        protected void onPreExecute()
        {
            try {
                Dialog.setMessage("Doing something...");
                Dialog.show();
            }catch (Exception e)
            {
                e.printStackTrace();
            }

        }

        @Override
        protected void onPostExecute(Integer result)
        {

            if(result==0)
            {
                //do some thing
            }
            // after completed finished the progressbar
            Dialog.dismiss();
        }

        @Override
        protected Integer doInBackground(Void... params) {

            mDatabase.child("version_1_5").child("title").addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    String temp = dataSnapshot.getValue(String.class);
                    title.setText(temp);
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });

            mDatabase.child("version_1_5").child("author").addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    String temp = dataSnapshot.getValue(String.class);
                    author.setText(temp);
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });

            mDatabase.child("version_1_5").child("article").addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    String temp = dataSnapshot.getValue(String.class);
                    article.setText(temp);
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });

            return 0;
        }


    }
}


</code>
</pre>

JSON树结构：

Root
    Version_1_5
        Title:TitleValue
        Author:AuthorValue
        Article:ArticleValue

Answer 1

您应该使用 addListenerForSingleValueEvent 从节点获取数据一次，而不是针对每个节点

private ProgressDialog Dialog = new ProgressDialog(LastPage.this);
Dialog.setMessage("Doing something...");
Dialog.show();
mDatabase.child("version_1_5").addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot Snapshot : dataSnapshot.getChildren()) {
            if(Snapshot.getKey().toString().equalsIgnoreCase("Title")){
                String temp = dataSnapshot.getValue(String.class);
                title.setText(temp);
            }
            else if(Snapshot.getKey().toString().equalsIgnoreCase("Author")){
                String temp = dataSnapshot.getValue(String.class);
                author.setText(temp);
            }
            else if(Snapshot.getKey().toString().equalsIgnoreCase("Article")){
                 String temp = dataSnapshot.getValue(String.class);
                article.setText(temp);
            }
        }
        Dialog.hide();
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});