Firebase DB:检查节点是否没有子节点? [英] Firebase DB: Check if node has no children?

问题描述

如何确定Firebase数据库节点是否没有子节点?似乎获取数据的唯一方法是使用侦听器，并且仅当添加或删除某些内容时它们才会触发.换句话说，如果没有孩子，什么也不会开火.

How do I find out if a Firebase DB node has no children? Seems the only way to get data is with listeners, and they only fire when something is added or removed. In other words, if there are no children, nothing will fire.

推荐答案

您可以使用addValueEventListener，在onDataChange中，您将有某种方法可以检查没有孩子.
addValueEventListener之所以能够工作，是因为对该 docs 进行编码>

You can use addValueEventListener, and in onDataChange you will have some way to check no children.
The addValueEventListener will work because arcoding this docs

在附加侦听器时触发此方法一次，然后再次触发 每当数据(包括子项)发生变化

This method is triggered once when the listener is attached and again every time the data, including children, changes

ref.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot snapshot) {
        // As cricket_007 we also can use hasChildren or getChildrenCount
        if(!snapshot.hasChildren()){
            // db has no children
        }

        // OR this way
        if(snapshot.getChildrenCount() == 0){
            // db has no children
        }

        // OR this way
        for (DataSnapshot postSnapshot : snapshot.getChildren()) {
            // db has no children
        }
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {
    }
});

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