[英]How to retrieve a specific data from a node in Firebase Realtime Database using Android Studio?
[英]How to retrieve data for a specific child in firebase database - android studio/ java?
我想检索特定孩子的数据,我该如何编写代码? 我尝试了很多,但没有奏效:"([ 就像在我的数据库中一样,如何为特定孩子(如 lubna)获取任务并获取所有孩子的任务?
初始化类变量:
private DatabaseReference mDatabase;
mDatabase = FirebaseDatabase.getInstance().getReference();
private DatabaseReference lubnaRef = mDatabase.child("tasks/Lubna");
然后出于测试目的,我假设您在活动的onCreate
方法中调用它,假设您没有数据模型,您将添加以下内容:
lubnaRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
//These are all of your children.
Map<String, Object> lubna = (Map<String, Object>) dataSnapshot.getValue();
for (String childKey: lubna.keySet()) {
//childKey is your "-LQka.. and so on"
//Your current object holds all the variables in your picture.
Map<String, Object> currentLubnaObject = (Map<String, Object>) lubna.get(childKey);
//You can access each variable like so: String variableName = (String) currentLubnaObject.get("INSERT_VARIABLE_HERE"); //data, description, taskid, time, title
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
要解决此问题,请使用以下代码行:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference lubnaRef = rootRef.child("tasks").child("Lubna");
ValueEventListener valueEventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String title = ds.child("title").getValue(String.class);
Log.d(TAG, title);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Log.d(TAG, databaseError.getMessage());
}
};
lubnaRef.addListenerForSingleValueEvent(valueEventListener);
与获取title
方式相同,您还可以获取其他值。 logcat 中的输出将是:
Homework
//and so on
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