來自getValue（）的Firebase對象爲空

Question

dataSnapshot.getValue()返回null即使我非常確定我指的是正確的路徑，並且在我的JSON樹中存在該鍵的值。它是這樣發送的：dbreference.setValue(true);。

Answer 1

也許你沒有正確獲取數據。下面是我用它來得到火力點數據，可以幫助你的示例代碼：

private DatabaseReference mDatabase; 

    mDatabase = FirebaseDatabase.getInstance().getReference(); 
    mDatabase.child("user_details").child("user_id").addListenerForSingleValueEvent(new ValueEventListener() { 
    @Override 
    public void onDataChange(DataSnapshot dataSnapshot) { 
     String name = null, surname = null, email = null, phone = null, bd = null, gender = null; 
     for (DataSnapshot child : dataSnapshot.getChildren()) { 
      if (child.getKey().equals("firstName")) { 
       name = child.getValue().toString(); 
      } 
      if (child.getKey().equals("lastName")) { 
       surname = child.getValue().toString(); 
      } 
      if (child.getKey().equals("birthday")) { 
       bd = child.getValue().toString(); 
      } 
      if (child.getKey().equals("email")) { 
       email = child.getValue().toString(); 
      } 
      if (child.getKey().equals("gender")) { 
       gender = child.getValue().toString(); 
      } 
      if (child.getKey().equals("phone")) { 
       phone = child.getValue().toString(); 
      } 
     } 
    } 

    @Override 
    public void onCancelled(DatabaseError databaseError) { 
    } 
});