[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?
我想檢索特定孩子的數據,我該如何編寫代碼? 我嘗試了很多,但沒有奏效:"([ 就像在我的數據庫中一樣,如何為特定孩子(如 lubna)獲取任務並獲取所有孩子的任務?
初始化類變量:
private DatabaseReference mDatabase;
mDatabase = FirebaseDatabase.getInstance().getReference();
private DatabaseReference lubnaRef = mDatabase.child("tasks/Lubna");
然后出於測試目的,我假設您在活動的onCreate
方法中調用它,假設您沒有數據模型,您將添加以下內容:
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) {
}
});
要解決此問題,請使用以下代碼行:
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);
與獲取title
方式相同,您還可以獲取其他值。 logcat 中的輸出將是:
Homework
//and so on
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