ChildEventListener必须实现onChildChanged [英] ChildEventListener must implement onChildChanged

问题描述

这让我发疯.我使用的是"onChildAdded"，如果我将其切换为"onChildChanged"，它会要求我切换回"onChildAdded".我不知道为什么要这么做.

This is driving me insane. I'm using "onChildAdded" and if I switch it to "onChildChanged" then it asks me to switch back to "onChildAdded". I have no idea why it's doing this.

这是我的代码:

Query queryRecycler = mDatabase.limitToLast(5);
        queryRecycler.addChildEventListener(new ChildEventListener() {

            public void onChildAdded(DataSnapshot dataSnapshot, String previousKey) {
                messageList.add(dataSnapshot.getValue(Message.class));
                mMessageAdapter.notifyDataSetChanged();
            }

        });

以及完整的错误:

类从ChildEventListener派生的匿名类"必须是 声明抽象或实现抽象方法 'ChildEventListener'中的'onChildChanged(DataSnapshot，String)'

Class 'Anonymous class derived from ChildEventListener' must either be declared abstract or implement abstract method 'onChildChanged(DataSnapshot, String)' in 'ChildEventListener'

推荐答案

如果要实现 ChildEventListener ，则应覆盖onChildAdded，onChildChanged，onChildRemoved，onChildMoved.即使您不想要它. (来自 firebase 的代码示例)

If you want to implement ChildEventListener, you should override onChildAdded,onChildChanged, onChildRemoved, onChildMoved. even you do not want it. (Code example from firebase)

ChildEventListener childEventListener = new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String previousChildName) {
        Log.d(TAG, "onChildAdded:" + dataSnapshot.getKey());

        // A new comment has been added, add it to the displayed list
        Comment comment = dataSnapshot.getValue(Comment.class);

        // ...
    }

    @Override
    public void onChildChanged(DataSnapshot dataSnapshot, String previousChildName) {
        Log.d(TAG, "onChildChanged:" + dataSnapshot.getKey());

        // A comment has changed, use the key to determine if we are displaying this
        // comment and if so displayed the changed comment.
        Comment newComment = dataSnapshot.getValue(Comment.class);
        String commentKey = dataSnapshot.getKey();

        // ...
    }

    @Override
    public void onChildRemoved(DataSnapshot dataSnapshot) {
        Log.d(TAG, "onChildRemoved:" + dataSnapshot.getKey());

        // A comment has changed, use the key to determine if we are displaying this
        // comment and if so remove it.
        String commentKey = dataSnapshot.getKey();

        // ...
    }

    @Override
    public void onChildMoved(DataSnapshot dataSnapshot, String previousChildName) {
        Log.d(TAG, "onChildMoved:" + dataSnapshot.getKey());

        // A comment has changed position, use the key to determine if we are
        // displaying this comment and if so move it.
        Comment movedComment = dataSnapshot.getValue(Comment.class);
        String commentKey = dataSnapshot.getKey();

        // ...
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Log.w(TAG, "postComments:onCancelled", databaseError.toException());
        Toast.makeText(mContext, "Failed to load comments.",
                Toast.LENGTH_SHORT).show();
    }
};
ref.addChildEventListener(childEventListener);

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