在嘗試使用 orderByChild() 和 startAt() 對數據進行排序和過濾的代碼時，將 Value 設為 null我在下面附上了數據結構和結果的圖像，我以數據快照的形式獲得了這些圖像。代碼如下Query queryMeal = FirebaseDatabase.getInstance().getReference("meals"); queryMeal.orderByChild("meal_name").startAt("ggh").addListenerForSingleValueEvent(new ValueEventListener() { @Override public void onDataChange(@NonNull DataSnapshot dataSnapshot) { Log.e("Query DataSnapShot",""+dataSnapshot.toString()); } @Override public void onCancelled(@NonNull DatabaseError databaseError) { } });
2 回答
開滿天機
TA貢獻1786條經驗 獲得超13個贊
要解決此問題，請更改以下代碼行：
Query queryMeal = FirebaseDatabase.getInstance().getReference("meals");
ueryMeal.orderByChild("meal_name").startAt("ggh").addListenerForSingleValueEvent();
到
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
Query queryMeal = FirebaseDatabase.getInstance().getReference().child("meals").child(uid);
ueryMeal.orderByChild("meal_name").startAt("ggh").endAt("ggh" + "\uf8ff").addListenerForSingleValueEvent();
編輯：
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference mealsRef = rootRef.child("meals");
ValueEventListener valueEventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot uidSnapshot : dataSnapshot.getChildren()) {
String uid = uidSnapshot.getKey();
DatabaseReference uidRef = rootRef.child("meals").child(uid).startAt("ggh").endAt("ggh" + "\uf8ff");
ValueEventListener eventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String mealName = ds.child("meal_name").getValue(String.class);
Log.d(TAG, mealName);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Log.d(TAG, databaseError.getMessage());
}
};
uidRef.addListenerForSingleValueEvent(eventListener);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Log.d(TAG, databaseError.getMessage());
}
};
mealsRef.addListenerForSingleValueEvent(valueEventListener);
楊魅力
TA貢獻1811條經驗 獲得超6個贊
在你的 onDataChange 方法中做這樣的事情
if(dataSnapshot != null){
Log.e("Query DataSnapShot",""+dataSnapshot.getValue().toString());
}
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