android - 从 firebase 实时数据库复制数据

Question

有一种方法可以从 firebase 实时数据库向我的列表添加数据:

private fun getTargetsFromDb() {
        val uid = firebaseUser!!.uid
        val targetsRef = databaseReference?.child("targets")?.child("users")?.child(uid)?.child("targets")
        val valueEventListener = object : ValueEventListener {
            override fun onDataChange(dataSnapshot: DataSnapshot) {
                for (targetSnapshot in dataSnapshot.children) {
                    val target = targetSnapshot.getValue(Target::class.java)
                    target?.let { targetList.add(it) }
                }
                recyclerView?.adapter = adapter
            }

            override fun onCancelled(databaseError: DatabaseError) {
                Log.d("some", "Error trying to get targets for ${databaseError.message}")
            }
        }
        targetsRef?.addListenerForSingleValueEvent(valueEventListener)
    }

但有时当我从一个 fragment 跳到另一个 fragment 时，我有一个重复的数据列表。

问:我需要在某个地方删除 targetList 的数据吗？

Answer 1

这可以帮助您清除旧数据并将新数据存储在列表中。

private fun getTargetsFromDb() {
        val uid = firebaseUser!!.uid
        val targetsRef = databaseReference?.child("targets")?.child("users")?.child(uid)?.child("targets")
        val valueEventListener = object : ValueEventListener {
            override fun onDataChange(dataSnapshot: DataSnapshot) {
                targetList.clear()
                for (targetSnapshot in dataSnapshot.children) {
                    val target = targetSnapshot.getValue(Target::class.java)
                    target?.let { targetList.add(it) }
                }
                recyclerView?.adapter = adapter
            }

            override fun onCancelled(databaseError: DatabaseError) {
                Log.d("some", "Error trying to get targets for ${databaseError.message}")
            }
        }
        targetsRef?.addListenerForSingleValueEvent(valueEventListener)
    }

上面的代码将检查响应是否成功，然后它将清除列表并存储值，或者它不会清除列表并只给你异常。