[英]Getting Data from Firebase realtime database, Android Studio, Java
I am looking for a way to get data from the firebase real-time database in a format like an array[] or a String. 我正在寻找一种从Firebase实时数据库中以array []或String之类的格式获取数据的方法。
My database looks like this: Link to image of database 我的数据库如下所示: 链接到数据库的图像
Or: Database | -->Users | -->UID1 -->UID2
或:
Database | -->Users | -->UID1 -->UID2
Database | -->Users | -->UID1 -->UID2
This is at the root of the database I want to get a list of all of the UIDs in the "Users" child. 这是数据库的根目录,我想获取“用户”子级中所有UID的列表。 This is the code I have so far and am a bit stuck on:
这是我到目前为止的代码,有点儿卡住了:
DatabaseReference databaseReference = firebaseDatabase.getReference("Users");
databaseReference.addValueEventListener(
new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
String UIDs = dataSnapshot.getValue(String.class);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
I am a bit of a rookie as it comes to java, android studio, and firebase. 在Java,Android Studio和Firebase方面,我还是个菜鸟。 I am trying to get the data in a format I know how to use like a String or an Array[] of Strings.
我正在尝试以一种我知道如何使用的格式来获取数据,例如字符串或字符串Array []。 I looked around if other people had maybe asked the same question, but I could get the answers to those questions to work/didn't understand them.
我环顾四周,也许其他人也问过同样的问题,但是我可以得到这些问题的答案,使他们工作/不理解。 Thanks in advance for your time!
在此先感谢您的时间!
You can try this: 您可以尝试以下方法:
DatabaseReference ref=
FirebaseDatabase.getInstance().getReference("Users");
ref.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
int i = 0;
for(DataSnapshot d : dataSnapshot.getChildren()) {
name[i] = d.getKey();
i++;
}
}
}//onDataChange
@Override
public void onCancelled(DatabaseError error) {
}//onCancelled
});
name[] is an array of strings! name []是一个字符串数组!
For your above question I will give both ways: ArrayList or String with delimiters 对于上述问题,我将同时给出两种方式:ArrayList或带定界符的字符串
ArrayList<String> uids = new ArrayList<String>();
FirebaseDatabase.getInstance().getReference("Users").addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
for(DataSnapshot snapshot : dataSnapshot.getChildren()) {
uids.add(snapshot.getKey());
}
}
}
@Override
public void onCancelled(DatabaseError error) {
}
});
For String 对于字符串
String uids = ""; 字符串uids =“”;
FirebaseDatabase.getInstance().getReference("Users").addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
for(DataSnapshot snapshot : dataSnapshot.getChildren()) {
uids += snapshot.getKey() + ",";
}
}
}
@Override
public void onCancelled(DatabaseError error) {
}
});
This gives an output such as: uid1,uid2,uid3,.....uidn, 这给出了如下输出:uid1,uid2,uid3,..... uidn,
To get the a list of uids, please use the following code: 要获取uid列表,请使用以下代码:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference usersRef = rootRef.child("Users");
ValueEventListener valueEventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
List<String> list = new ArrayList<>();
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String uid = ds.getKey();
list.add(uid);
}
//Do what you need to do with your list
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
}
};
usersRef.addListenerForSingleValueEvent(valueEventListener);
I recommend you to use the list only inside the callback otherwise it will be empty. 我建议您仅在回调内部使用列表,否则它将为空。 If you want to use it outside the
onDataChange()
method, I recommend you see the last part of my anwser from this post in which I have explained how it can be done using a custom callback. 如果你想使用它的外
onDataChange()
方法,我建议你看我anwser从这个最后的部分后 ,其中我已经解释了如何可以使用自定义的回调来完成。 You can also take a look at this video for a better understanding. 您也可以观看此视频 ,以更好地理解。
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