Android的Firebase檢索數據回到gridView

我是新來的編程，我剛開始做我的第一個Android項目。我一直被困在這個問題上幾個小時，仍然不知道爲什麼它不起作用。以下是數據結構。Android的Firebase檢索數據回到gridView

我想補充的期刊爲各自的用戶，那我實現了addJournal（）函數工作。但是當我從數據庫中取回這些日誌到gridView時它崩潰了。

下面是如何添加日誌下面的數據庫：

 firebaseAuth = FirebaseAuth.getInstance(); 
     firebaseUser = firebaseAuth.getCurrentUser(); 
     journalReference=FirebaseDatabase.getInstance().getReference(); 

     String journalName = etJournalName.getText().toString().trim(); 
     String companyName = etCompanyName.getText().toString().trim(); 
     String journalColor = "blankForNow"; 
     String userID = firebaseUser.getUid(); 
     String journalID = journalReference.push().getKey(); 

     //validation 
     if (TextUtils.isEmpty(journalName)){ 
      etJournalName.setError("Journal name must not be empty"); 
     } else if (TextUtils.isEmpty(companyName)){ 
      etCompanyName.setError("Company name must not be empty"); 
     } else { 
      //storing data to the database... 
      Journal journal = new Journal(journalID, userID, journalName, companyName, journalColor); 
      journalReference.child("users") 
        .child(userID) 
        .child("journals") 
        .child(journalID).setValue(journal); 
     }

這裏就是我如何檢索數據如下：

DatabaseReference journalRef = 
    FirebaseDatabase.getInstance().getReference(); 
    journalRef.child("users") 
    .child(userID) 
    .child("journals").addChildEventListener(new ChildEventListener() { 
     @Override 
     public void onChildAdded(DataSnapshot dataSnapshot, String s) { 
      journalArrayList.clear(); 
      for (DataSnapshot journalDS : dataSnapshot.getChildren()) { 
       Journal journal = journalDS.getValue(Journal.class); 
       journalArrayList.add(journal); 
      } 
      gridViewAdapter = new GridViewAdapter(MainActivity.this, journalArrayList); 
      gridView.setAdapter(gridViewAdapter); 
     } 

     @Override 
     public void onChildChanged(DataSnapshot dataSnapshot, Strin

有人能幫助我嗎？在此先感謝

來源

2017-09-01 Jamen

你可以在這裏發佈錯誤日誌嗎？ – akhilesh0707

請發佈您的錯誤日誌。提前致謝！ – barotia

只是找出我可以找到日誌的位置... – Jamen

使用addListenerForSingleValueEvent insted的addChildEventListener

希望這可以幫助你

DatabaseReference journalRef =FirebaseDatabase.getInstance().getReference(); 
journalRef.child("users").child(userID).child("journals").addListenerForSingleValueEvent(new ValueEventListener() { 
    @Override 
    public void onDataChange(DataSnapshot dataSnapshot) { 
     journalArrayList.clear(); 
     for (DataSnapshot journalDS : dataSnapshot.getChildren()) { 
      Journal journal = journalDS.getValue(Journal.class); 
      journalArrayList.add(journal); 
     } 
     gridViewAdapter = new GridViewAdapter(MainActivity.this, journalArrayList); 
     gridView.setAdapter(gridViewAdapter); 
    } 

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

編輯

ValueEventListener得到的單束團，所有的數據，其中爲ChildEventListener GET數據逐個記錄爲特定節點。我建議您嘗試一下。爲每個ValueEventListener和ChildEventListener片段檢查行爲

編輯1

你得到NullPointerException異常，只是因爲你沒有初始化journalArrayList列表

初始化列表

journalArrayList=new ArrayList<>()

編輯2您可以使用map獲得價值解決方案

for (DataSnapshot journalDS : dataSnapshot.getChildren()) { 
    Map<String, String> map = (Map<String, String>) journalDS.getValue(); 
    String journalName = map.get("journalName"); 
    String companyName = map.get("companyName"); 
    String journalColor = map.get("journalColor"); 
    String userID = map.get("userID"); 
    String journalID = map.get("journalID"); 
    Journal journal = new Journal(journalID, userID, journalName, companyName, journalColor); 
    journalArrayList.add(journal); 
}

來源

2017-09-01 10:19:59 akhilesh0707

致命異常：主進程：com.cabbage.sdpjournal，PID：5840 java.lang.NullPointerException：嘗試在空對象引用在com.cabbage.sdpjournal.MainActivity $ 1.onDataChange（MainActivity.java:75） – Jamen

@Jamen上調用虛擬方法'void java.util.ArrayList.clear（）'只是因爲你得到了空指針錯誤你不是initiliaze你的journalArrayList.clear（）; – akhilesh0707

@ akhilesh0707我解決了它像你說的改變addChildEvent addValueEvent ...謝謝 – Jamen

嘗試下面的代碼，使用Get和set方法。

public class Journal { 
    private String journalID; 
    private String userID; 
    private String journalName; 
    private String companyName; 
    private String journalColor; 

    public Journal() { 
    } 

    public Journal(String journalID, String userID, String journalName, String companyName, String journalColor) { 
     this.journalID = journalID; 
     this.userID = userID; 
     this.journalName = journalName; 
     this.companyName = companyName; 
     this.journalColor = journalColor; 
    } 

    public String getJournalID() { 
     return journalID; 
    } 

    public void setJournalID(String journalID) { 
     this.journalID = journalID; 
    } 

    public String getUserID() { 
     return userID; 
    } 

    public void setUserID(String userID) { 
     this.userID = userID; 
    } 

    public String getJournalName() { 
     return journalName; 
    } 

    public void setJournalName(String journalName) { 
     this.journalName = journalName; 
    } 

    public String getCompanyName() { 
     return companyName; 
    } 

    public void setCompanyName(String companyName) { 
     this.companyName = companyName; 
    } 

    public String getJournalColor() { 
     return journalColor; 
    } 

    public void setJournalColor(String journalColor) { 
     this.journalColor = journalColor; 
    } 
}

來源

2017-09-01 11:16:14 Jamen

d /期刊：==> DataSnapshot {鍵= -KsvqM79AsS1bPUgtngB，值= {用戶ID = qAzq0h3E8oaUn09SkG0hWhFfTDT2，journalName = Journals001，journalID = -KsvqM79AsS1bPUgtngB，公司名稱= com001，journalColor = blankForNow}} 09-01 21：20：20.364 30374-30374/com.cabbage.sdpjournal D/Journal：==> DataSnapshot {key = -KsvzWaNFsYX488MLSIK，value = {userID = qAzq0h3E8oaUn09SkG0hWhFfTDT2，journalName = Journal007，journalID = -KsvzWaNFsYX488MLSIK，companyName = com007，journalColor = blankForNow}} 09-01 21：20：20.364 30374-30374/com.cabbage.sdpjournal D/Journal：==> DataSnapshot {key = -KsvzdIrgwFG3DaLXyt1，value = {userID = qAzq0h3E8oaUn09SkG0hWhFfTDT2，journalName = Journal008，journalID = -ks vzdIrgwFG3DaLXyt1，companyName = com008，journalColor = blankForNow}} 09-01 21：20：20.365 30374-30374/com.cabbage。sdpjournal D/Journal：==> DataSnapshot {key = -KswCFyIifHf-smTXxu，value = {userID = qAzq0h3E8oaUn09SkG0hWhFfTDT2，journalName = Journals008，journalID = -KswCFyIifHf - smTXxu，companyName = com008，journalColor = blankForNow}} 09-01 21：20：20.365 30374-30374/com.cabbage.sdpjournal D/Journal：==> DataSnapshot {key = -KswV-O82jgtGOaRr6BK，value = {userID = qAzq0h3E8oaUn09SkG0hWhFfTDT2，journalName = journal009，journalID = -KswV-O82jgtGOaRr6BK，companyName = com009，journalColor = blankForNow}}

來源

2017-09-01 11:22:35 Jamen

Android的Firebase檢索數據回到gridView

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