[英]Can't pass null for argument 'pathString' in child()? This the error I'm getting when retrieving data from firebase
[英]How can i fix this error retrieving data from firebase
這是我存儲在數據庫中的數據的圖像。
'E/AndroidRuntime: 致命異常: main
Process: com.example.pahalunitedfoundation, PID: 31028
com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.pahalunitedfoundation.mainModel
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(CustomClassMapper.java:436)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:232)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:80)
at com.google.firebase.database.DataSnapshot.getValue(DataSnapshot.java:203)
at com.firebase.ui.database.ClassSnapshotParser.parseSnapshot(ClassSnapshotParser.java:29)
at com.firebase.ui.database.ClassSnapshotParser.parseSnapshot(ClassSnapshotParser.java:15)
at com.firebase.ui.common.BaseCachingSnapshotParser.parseSnapshot(BaseCachingSnapshotParser.java:36)
at com.firebase.ui.common.BaseObservableSnapshotArray.get(BaseObservableSnapshotArray.java:52)
at com.firebase.ui.database.FirebaseRecyclerAdapter.getItem(FirebaseRecyclerAdapter.java:108)
at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:148)
at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7254)
at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7337)
at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6194)
at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6460)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6300)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6296)
at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2330)
at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1631)
at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1591)
at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:668)
at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4309)
at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:4012)
at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4578)
at android.view.View.layout(View.java:23059)
at android.view.ViewGroup.layout(ViewGroup.java:6479)
at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1873)
at android.view.View.layout(View.java:23059)
at android.view.ViewGroup.layout(ViewGroup.java:6479)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at android.view.View.layout(View.java:23059)
at android.view.ViewGroup.layout(ViewGroup.java:6479)
at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:536)
at android.view.View.layout(View.java:23059)
at android.view.ViewGroup.layout(ViewGroup.java:6479)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at android.view.View.layout(View.java:23059)
at android.view.ViewGroup.layout(ViewGroup.java:6479)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
at android.view.View.layout(View.java:23059)
at android.view.ViewGroup.layout(ViewGroup.java:6479)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at com.android.internal.policy.DecorView.onLayout(DecorView.java:804)
at android.view.View.layout(View.java:23059)
at android.view.ViewGroup.layout(ViewGroup.java:6479)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3622)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:3082)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:2075)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8512)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1076)
at android.view.Choreographer.doCallbacks(Choreographer.java:897)
at android.view.Choreographer.doFrame(Choreographer.java:826)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1061)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:236)
at android.app.ActivityThread.main(ActivityThread.java:8056)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:656)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:967)
下面是寫在我的主要 main.java 文件中的代碼,我已經刪除了這個問題中的導入,因為它顯示錯誤
package com.example.pahalunitedfoundation;
public class Events extends AppCompatActivity {
eventAdapter eventAdapter;
RecyclerView recyclerView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_events);
recyclerView = findViewById(R.id.rv);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
FirebaseRecyclerOptions<mainModel> options =
new FirebaseRecyclerOptions.Builder<mainModel>()
.setQuery(FirebaseDatabase.getInstance().getReference().child("data"), mainModel.class)
.build();
eventAdapter = new eventAdapter(options);
recyclerView.setAdapter(eventAdapter);
}
@Override
protected void onStart() {
super.onStart();
eventAdapter.startListening();
}
@Override
protected void onStop() {
super.onStop();
eventAdapter.startListening();
}
}
下面是我的適配器 class 的代碼(減去進口)
package com.example.pahalunitedfoundation;
public class eventAdapter extends FirebaseRecyclerAdapter <mainModel,eventAdapter.myViewHolder> {
/**
* Initialize a {@link RecyclerView.Adapter} that listens to a Firebase query. See
* {@link FirebaseRecyclerOptions} for configuration options.
*
* @param options
*/
public eventAdapter(@NonNull FirebaseRecyclerOptions<mainModel> options) {
super(options);
}
@Override
protected void onBindViewHolder(@NonNull myViewHolder holder, int position, @NonNull mainModel model) {
holder.ename.setText(model.getEname());
holder.date.setText(model.getDate());
holder.description.setText(model.getDescription());
Glide.with(holder.img.getContext())
.load(model.getSurl())
.placeholder(R.drawable.common_google_signin_btn_icon_dark)
.circleCrop()
.error(R.drawable.common_google_signin_btn_icon_dark)
.into(holder.img);
}
@NonNull
@Override
public myViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.event_item,parent,false);
return new myViewHolder(view);
}
class myViewHolder extends RecyclerView.ViewHolder{
// enter code here
CircleImageView img;
TextView ename,date,description;
public myViewHolder(@NonNull View itemView) {
super(itemView);
img = (CircleImageView)itemView.findViewById(R.id.img1);
ename = itemView.findViewById(R.id.enametext);
date = itemView.findViewById(R.id.Date);
description = itemView.findViewById(R.id.description);
}
}
}
幾個問題:監聽器可能應該在 onStop 期間停止
@Override
protected void onStop() {
super.onStop();
eventAdapter.stopListening(); // was startListening
}
此外,堆棧跟蹤似乎直接與缺少mainModel
class 的任何實際適配器代碼有關。 如果您可以包含此 class 可能會有所幫助。 現在,recyclerview 已設置,只需嘗試通過傳遞data
中的任何內容來實例化mainModel
,我認為它是一個字符串。
FirebaseRecyclerOptions<mainModel> options =
new FirebaseRecyclerOptions.Builder<mainModel>()
.setQuery(FirebaseDatabase.getInstance().getReference().child("data"), mainModel.class)
.build();
如果mainModel
的構造函數不采用String
,則需要制作適配器或mainModel
需要更新以采用String
錯誤顯示firebase數據庫的data
節點中有字符串數據。 所以這行代碼無法將該字符串轉換為mainModel
類型。
FirebaseRecyclerOptions<mainModel> options =
new FirebaseRecyclerOptions.Builder<mainModel>()
.setQuery(FirebaseDatabase.getInstance().getReference().child("data"), mainModel.class)
.build();
因此,請注意 firebase 控制台上的數據庫,如果您有任何內部data
節點,請刪除字符串。
最佳實踐,
總是給你的 class 一個大寫的名字。
例如,
這樣取名,
public class MainModel
取而代之的是,
public class mainModel
當您傳遞以下參考時:
FirebaseDatabase.getInstance().getReference().child("data")
連同“mainModel” class 到 FirebaseRecyclerOptions.Builder 的“setQuety()”方法,這意味着您要使用 Firebase-UI 庫來顯示存在於其中的所有“mainModel”對象:
root -> data
這實際上是不可能的,因為在該引用下它只存在一個字符串類型的子項,因此出現以下錯誤:
com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.pahalunitedfoundation.mainModel
要解決這個問題,您需要在“數據”節點下添加一個額外的級別。 這可以使用 DatabaseReference 的push()方法簡單地完成。 因此,當您在上述參考中添加 object 時,請按如下方式添加:
DatabaseReference db = FirebaseDatabase.getInstance().getReference();
DatabaseReference dataRef = db.child("data");
dataRef.push().setValue(mainModelObject);
這樣,您的數據庫架構應如下所示:
Firebase-root
|
--- data
|
--- $pushedId
|
--- date: "dd/mm/yyyy"
|
--- description: "this is a des"
|
--- name: "Pahal..."
|
--- surl: "https://..."
獲取數據的代碼可能保持不變。
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