android - 访问 firebase 回收器适配器中的子节点

Question

我有我的firebaseRecyclerAdapter，它的populateViewHolder如下

Query queryRef = chatRef.orderByKey();
queryRef.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot snapshot, String previousChild) {
        System.out.println(snapshot.getKey());

        for (DataSnapshot snapshot1 : snapshot.getChildren()) {
            final String firstname = snapshot.getKey();
            chatViewHolder.setName(firstname);

            chatViewHolder.mView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    //Log.w(TAG, "You clicked on "+position);
                    //String firstname = tList.getFirstname();
                    //String lastname = tList.getLastname();
                    //firstname = firstname.substring(0, 1).toUpperCase() + firstname.substring(1); //convert first string to uppercase
                    //lastname = lastname.substring(0, 1).toUpperCase() + lastname.substring(1);// same thing happening here
                    //String name = (firstname + " " + lastname); // concatenate firstname and lastname variable.

                    Intent intent = new Intent(getActivity(), MainChat.class); //change to onclick
                    intent.putExtra("fullname", firstname);
                    //you can name the keys whatever you like
                    //intent.putExtra("image", userList.getImgUrl().toString()); //note that all these values have to be primitive (i.e boolean, int, double, String, etc.)
                    startActivity(intent);

                }
            });
        }

这是用回收器适配器备份的，我的数据库看起来像

users
   uid
      conversations
                   sLname + sFname
                           -KyF........:
                                  message: hi
                                  timestamp: ServerValue.timestamp
                            -KyFr......:
                                  message:hello
                                  timestamp: ServerValue.timestamp

firebaseRecyclerAdapter的实现

RecyclerView recycler = (RecyclerView) rootView.findViewById(R.id.recyclerview4);
recycler.setHasFixedSize(true);
recycler.setLayoutManager(new LinearLayoutManager(getActivity()));


FirebaseRecyclerAdapter mAdapter = new FirebaseRecyclerAdapter<ChatList, ChatHolder>(ChatList.class, R.layout.chatlistrow, ChatHolder.class, chatRef) {
    @Override
    public void populateViewHolder(final ChatHolder chatViewHolder, final ChatList chatList, final int position) {

        //try catch block to catch events of no posts, it will most likely return a null error, so I'm catching it, else
        //find its exception and catch itef

        contactList = new ArrayList<String>();

         //start here and getkey for everyone

        contactList.add(chatRef.getKey());

        //String firstname = chatRef.getKey();
        //chatViewHolder.setName(firstname);

        Query queryRef = chatRef.orderByKey();
        queryRef.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot snapshot, String previousChild) {
                System.out.println(snapshot.getKey());

                for (DataSnapshot snapshot1 : snapshot.getChildren()) {
                    final String firstname = snapshot.getKey();
                    chatViewHolder.setName(firstname);

                    chatViewHolder.mView.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            //Log.w(TAG, "You clicked on "+position);

                            Intent intent = new Intent(getActivity(), MainChat.class); //change to onclick
                            intent.putExtra("fullname", firstname);
                            //you can name the keys whatever you like
                            //intent.putExtra("image", userList.getImgUrl().toString()); //note that all these values have to be primitive (i.e boolean, int, double, String, etc.)
                            startActivity(intent);
                        }
                    });
                }
                //testing
            }

            @Override
            public void onChildChanged(DataSnapshot snapshot, String previousChild) {
            }

            @Override
            public void onChildMoved(DataSnapshot snapshot, String previousChild) {
            }

            @Override
            public void onChildRemoved(DataSnapshot snapshot) {
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
            }
            // ....
        });
    }
};
recycler.setAdapter(mAdapter);

我的export.json是

 "admin" : {
    "ZpMBDchTkPVh7El3EsIKEdmV28n1" : {
      "bio" : "",
      "conversations" : {
        "Chinwendu Chiebidolu" : {
          "-KYCaWdm7IJrF-yau0ES" : {
            "message" : "hello",
            "rfirstname" : "Chinwendu",
            "rimgUrl" : "",
            "rlastname" : "Chiebidolu",
            "rname" : "Chinwendu Chiebidolu",
            "timestamp" : 1480918181229,
            "userId" : "lgsmNM2LXuVq8NBoDwDCaoe5B613"
          }
        },
        "Damilola Aromiwe" : {
          "-KYBzfTc5xHCPGM06QIE" : {
            "message" : "hi",
            "rfirstname" : "Damilola",
            "rimgUrl" : "2124",
            "rlastname" : "Aromiwe",
            "rname" : "Damilola Aromiwe",
            "timestamp" : 1480907995851,
            "userId" : "ujNyb5erkSN7oS3aGZlXyc9Q0YJ2"
          },
          "-KYCYYkifzI-61dBKsTT" : {
            "message" : "hello",
            "rfirstname" : "Damilola",
            "rimgUrl" : "2124",
            "rlastname" : "Aromiwe",
            "rname" : "Damilola Aromiwe",
            "timestamp" : 1480917404523,
            "userId" : "ujNyb5erkSN7oS3aGZlXyc9Q0YJ2"
          },
          "-KYCZ19NM2yKinU5eSLt" : {
            "message" : "hello mr dammy, are you there? ",
            "rfirstname" : "Damilola",
            "rimgUrl" : "2124",
            "rlastname" : "Aromiwe",
            "rname" : "Damilola Aromiwe",
            "timestamp" : 1480917527734,
            "userId" : "ujNyb5erkSN7oS3aGZlXyc9Q0YJ2"
          }
        }
      },
      "email" : "toyosi@gmail.com",
      "firstname" : "Toyosi",
      "imgUrl" : "2124",
      "lastname" : "Yusuf",
      "name" : "toyosi",
      "parent" : true,
      "phone" : "",
      "teacher" : false,
      "userId" : "ZpMBDchTkPVh7El3EsIKEdmV28n1"
    }
  },
  "teachers" : {
    "inFa52OMArdKyUTMYrkRqWs50uD2" : {
      "bio" : "",
      "email" : "david@gmail.com",
      "firstname" : "David",
      "imgUrl" : "",
      "lastname" : "Akinyemi",
      "name" : "",
      "parent" : false,
      "phone" : "",
      "teacher" : true,
      "userId" : "inFa52OMArdKyUTMYrkRqWs50uD2"
    },
    "xITyS4TrbWXPBhHYAgz0ZsdyYFa2" : {
      "bio" : "",
      "email" : "ejura@gmail.com",
      "firstname" : "Ejura",
      "imgUrl" : "",
      "lastname" : "Ayeni",
      "name" : "",
      "parent" : false,
      "phone" : "",
      "teacher" : true,
      "userId" : "xITyS4TrbWXPBhHYAgz0ZsdyYFa2"
    }
  },
  "users" : {
    "HJ55v7xUGmXQN2o1AQFDG9JtzCy1" : {
      "bio" : "",
      "email" : "aurora@gmail.com",
      "firstname" : "",
      "imgUrl" : "",
      "lastname" : "",
      "name" : "",
      "parent" : true,
      "phone" : "",
      "teacher" : false,
      "userId" : "HJ55v7xUGmXQN2o1AQFDG9JtzCy1"
    },
    "KrVp7D6gLoZoH6WcHT5tmyqb3o53" : {
      "bio" : "",
      "email" : "akinyemidvd@gmail.com",
      "firstname" : "",
      "imgUrl" : "",
      "lastname" : "",
      "name" : "",
      "parent" : true,
      "phone" : "",
      "teacher" : false,
      "userId" : "KrVp7D6gLoZoH6WcHT5tmyqb3o53"
    },
    "lgsmNM2LXuVq8NBoDwDCaoe5B613" : {
      "bio" : "",
      "conversations" : {
        "Toyosi Yusuf" : {
          "-KYCaWdHGbWxsk8h7EWy" : {
            "message" : "hello",
            "sfirstname" : "Toyosi",
            "simageurl" : "2124",
            "slastname" : "Yusuf",
            "timestamp" : 1480918179544
          }
        }
      },
      "email" : "chinwe@gmail.com",
      "firstname" : "Chinwendu",
      "imgUrl" : "",
      "lastname" : "Chiebidolu",
      "name" : "",
      "parent" : true,
      "phone" : "",
      "teacher" : false,
      "userId" : "lgsmNM2LXuVq8NBoDwDCaoe5B613"
    },
    "ujNyb5erkSN7oS3aGZlXyc9Q0YJ2" : {
      "bio" : "",
      "conversations" : {
        "Toyosi Yusuf" : {
          "-KYBzfT_p8N2oW7oqSke" : {
            "message" : "hi",
            "sfirstname" : "Toyosi",
            "simageurl" : "2124",
            "slastname" : "Yusuf",
            "timestamp" : 1480907995531
          },
          "-KYCYYkfORU70Y1_PGug" : {
            "message" : "hello",
            "sfirstname" : "Toyosi",
            "simageurl" : "2124",
            "slastname" : "Yusuf",
            "timestamp" : 1480917401926
          },
          "-KYCZ19KyX8X5G25CEz5" : {
            "message" : "hello mr dammy, are you there? ",
            "sfirstname" : "Toyosi",
            "simageurl" : "2124",
            "slastname" : "Yusuf",
            "timestamp" : 1480917527335
          }
        }
      },
      "email" : "dammyaro@gmail.com",
      "firstname" : "Damilola",
      "imgUrl" : "2124",
      "lastname" : "Aromiwe",
      "name" : "",
      "parent" : true,
      "phone" : "",
      "teacher" : false,
      "userId" : "ujNyb5erkSN7oS3aGZlXyc9Q0YJ2"
    }
  }
}

chatList.class() 指向这里

package com.mordred.theschoolapp;

/**
 * Created by mordred on 11/29/16.
 */
public class ChatList {

    public String userId;
    public String rname;
    public String rlastname;
    public String rimageurl;

    public ChatList() {
        // Default constructor required for calls to DataSnapshot.getValue(User.class)
    }

    public String getFirstname() {
        return rname;
    }

    public void setFirstname(String firstname) {
        this.rname = firstname;
    }

    public String getLastname() {
        return rlastname;
    }

    public void setLastname(String lastname) {
        this.rlastname = lastname;
    }

    public String getImgUrl() {
        return rimageurl;
    }

    public void setImgUrl(String imgUrl) {
        this.rimageurl = imgUrl;
    }

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }
}

这里的问题是我试图在回收器适配器中递归地检索这些消息。但是在上面使用以前的代码，我只是不断重复第一条消息。谁能告诉我发生了什么事，我该如何解决？如果您需要任何其他信息，请直接询问。谢谢

Answer 1

看来您不了解 Firebase UI 数据库 的工作原理。完整的文档是 here ，您应该阅读该自述文件以了解其工作原理。

populateViewHolder 方法的工作原理几乎与 onChildAdded/onChildChanged 相同，它返回引用节点下的每个子节点。

所以它应该是这样的

chatRef = FirebaseDatabase.getInstance().getReference("users").child(uid).child("conversations");

...

@Override
public void populateViewHolder(final ChatHolder chatViewHolder, final ChatList chatList, final int position) {
    contactList = new ArrayList<String>();
    // this is what you want
    String fullName = mAdapter.getRef(position).getKey();
    contactList.add(fullName);

    ...
}

顺便说一句，您的 ChatList 模型类缺少属性，或者属性不反射(reflect)数据库中的键，因此某些方法可能返回 null 值。 Read and Write Data on Android