我對(duì) Java 比較陌生，使用比較器的整個(gè)排序讓我有點(diǎn)困惑。是否可以在不使用比較器的情況下按降序?qū)ο旅娲a的當(dāng)前輸出進(jìn)行排序？或者有沒有更簡(jiǎn)單的方法讓我理解如何對(duì)所述值進(jìn)行排序。myRef.addChildEventListener(new ChildEventListener() { @Override public void onChildAdded(@NonNull DataSnapshot dataSnapshot , String s) { Map<String, Object> userInfo = (Map<String, Object>)dataSnapshot.getValue(); String username = (String) userInfo.get("username"); Map<String, Long> steps = (Map<String, Long>) userInfo.get("steps"); long existingSteps = 0; for (Map.Entry<String, Long> step : steps.entrySet()) { existingSteps += Long.valueOf(step.getValue()); } arrayList.add(new String( username + " - " + "steps: " + existingSteps)); arrayAdapter = new ArrayAdapter<>(Leaderboard.this , android.R.layout.simple_list_item_1 , arrayList); listView.setAdapter(arrayAdapter);}此代碼的當(dāng)前輸出是：John Doe I - Steps: 79John Doe II - Steps: 111John Doe III - Steps: 0John Doe IV - Steps: 88John Doe V - Steps: 12John Doe VI - Steps: 0是否可以讓此代碼運(yùn)行以下輸出：John Doe II - Steps: 111John Doe IV - Steps: 88John Doe I - Steps: 79John Doe V - Steps: 12John Doe III - Steps: 0John Doe VI - Steps: 0數(shù)據(jù)庫(kù)結(jié)構(gòu)
1 回答
動(dòng)漫人物
TA貢獻(xiàn)1815條經(jīng)驗(yàn) 獲得超10個(gè)贊
我能想到的最簡(jiǎn)單的解決方案是在每個(gè)用戶對(duì)象下添加總步數(shù)作為新屬性。在這種情況下，您還需要做一件事，即根據(jù)您每天獲得的步數(shù)增加該屬性。您的新架構(gòu)應(yīng)如下所示：
Firebase-root
|
--- user
|
--- userId
|
--- steps
| |
| --- //daily steps
|
--- target: 100
|
--- username: "John Doe I"
|
--- totalNumberOfSteps: 111
要根據(jù)totalNumberOfSteps屬性按（升序）順序排列用戶，請(qǐng)使用以下代碼行：
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference userRef = rootRef.child("user");
Query query = userRef.orderByChild("totalNumberOfSteps");
ValueEventListener valueEventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String username = ds.child("username").getValue(String.class);
long totalNumberOfSteps = ds.child("totalNumberOfSteps").getValue(Long.class);
Log.d(TAG, username + " - Steps: " + totalNumberOfSteps);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
}
};
query.addListenerForSingleValueEvent(valueEventListener);
然后按降序排列，請(qǐng)從以下帖子中查看我的回答：
如何按升序或降序排列firebase數(shù)據(jù)庫(kù)數(shù)據(jù)？
最后，logcat 中的結(jié)果將是：
John Doe II - Steps: 111
John Doe IV - Steps: 88
John Doe I - Steps: 79
John Doe V - Steps: 12
John Doe III - Steps: 0
John Doe VI - Steps: 0
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