android - DataSnapshot 缺少一个没有参数的构造函数

Question

我正在我的应用程序中实现 Firebase Recyclerview UI。我已经实现了一个 recyclerview 适配器，它显示了以下异常。以下是我的适配器代码:

FirebaseRecyclerAdapter<DataSnapshot, MyHolder> recyclerAdapter = new FirebaseRecyclerAdapter<DataSnapshot, MyHolder>(
                DataSnapshot.class,
                R.layout.row_slots,
                MyHolder.class,
                databaseReference.child("slots").child(uid).child(dayOfWeek).child("time")
        ) {
            @Override
            protected void populateViewHolder(MyHolder viewHolder, DataSnapshot model, int position) {

                System.out.println("Key : "+model.getKey());

            }

        };

它显示以下异常:

如何使用 FirebaseRecyclerAdapter 获取快照值？

Answer 1

问题是 DataSnapShot 缺少一个无参数 构造函数，因此您不能像这样直接使用它。

Use some other model class instead.

像这样:

创建您自己的名为 FriendlyMessage 的模型:

public class FriendlyMessage {

private String text;
private String name;

// Created constructor with no Arguments 
public FriendlyMessage() {
}

public FriendlyMessage(String text, String name) {
    this.text = text;
    this.name = name;       
}

public String getText() {
    return text;
}

public void setText(String text) {
    this.text = text;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}
}

Most important thing we have created constructor with no Arguments which was missing in DataSnapShot

注意:上面的模型类只是一个例子，因为您是 firebase 的新手。您可以拥有自己的模型类和您自己的参数类型。

像这样在您的 Firebase Recyclerview 中使用它:

FirebaseRecyclerAdapter mFirebaseAdapter = new FirebaseRecyclerAdapter<FriendlyMessage, MyHolder>(
                    FriendlyMessage.class,
                    R.layout.row_slots,
                    MyHolder.class,
                    databaseReference.child("slots").child(uid).child(dayOfWeek).child("time")) {

        @Override
        protected void populateViewHolder(MyHolder viewHolder, FriendlyMessage friendlyMessage, int position)
        {

        }
    };

编辑:

It also matter how you are pushing the data on Database. Do it directly with your model class.

例如上面的模型 FriendlyMessage 像这样推送它:

FriendlyMessage friendlyMessage = new FriendlyMessage("message", "Username");
databaseReference.child(MESSAGES_CHILD).push().setValue(friendlyMessage);

这里您的 child() 将与我的实现有些不同，这只是一个示例。

用于收听特定的 DataSnapShot :

databaseReference.child("users").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                //The PUSH ID OP WANTED

                System.out.println("Push Id ---"+postSnapshot.getKey()); 
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    })

Explaining the above listener. It will give you the DataSnapShot Object for your every user who is falling inside your child "users". You can access Push id by getKey() method.