本文介绍了Firestore回收器适配器中的Getitem方法返回null的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
这是我得到的错误:
FATAL EXCEPTION: main
Process: neoncore.com.onepiece, PID: 19429
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object java.lang.reflect.Constructor.newInstance(java.lang.Object[])' on a null object reference
at com.google.android.gms.internal.zzevb$zza.zza(Unknown Source)
at com.google.android.gms.internal.zzevb.zza(Unknown Source)
at com.google.android.gms.internal.zzevb.zza(Unknown Source)
at com.google.firebase.firestore.DocumentSnapshot.toObject(Unknown Source)
at com.firebase.ui.firestore.ClassSnapshotParser.parseSnapshot(ClassSnapshotParser.java:23)
at com.firebase.ui.firestore.ClassSnapshotParser.parseSnapshot(ClassSnapshotParser.java:12)
at com.firebase.ui.common.BaseCachingSnapshotParser.parseSnapshot(BaseCachingSnapshotParser.java:35)
at com.firebase.ui.common.BaseObservableSnapshotArray.get(BaseObservableSnapshotArray.java:52)
at com.firebase.ui.firestore.FirestoreRecyclerAdapter.getItem(FirestoreRecyclerAdapter.java:83)
at neoncore.com.onepiece.activities.ChatDetail$3.getItem(ChatDetail.java:168)
at neoncore.com.onepiece.activities.ChatDetail$3.getItemViewType(ChatDetail.java:174)
at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:5657)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5589)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5585)
at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2231)
at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1558)
at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1518)
at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:585)
at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3719)
at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3436)
at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:3988)
at android.view.View.layout(View.java:16694)
at android.view.ViewGroup.layout(ViewGroup.java:5481)
at android.support.constraint.ConstraintLayout.onLayout(ConstraintLayout.java:1514)
at android.view.View.layout(View.java:16694)
at android.view.ViewGroup.layout(ViewGroup.java:5481)
at android.support.design.widget.CoordinatorLayout.layoutChild(CoordinatorLayout.java:1171)
at android.support.design.widget.CoordinatorLayout.onLayoutChild(CoordinatorLayout.java:856)
at android.support.design.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:875)
at android.view.View.layout(View.java:16694)
at android.view.ViewGroup.layout(ViewGroup.java:5481)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
at android.view.View.layout(View.java:16694)
at android.view.ViewGroup.layout(ViewGroup.java:5481)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1743)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1586)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1495)
at android.view.View.layout(View.java:16694)
at android.view.ViewGroup.layout(ViewGroup.java:5481)
当我在调试模式下运行应用程序时，我可以看到getItemcount方法的大小增加了，这意味着我正在获取数据，但随后会产生上述错误.上面的错误指向getItem方法，该方法为null，这是我的Firestore Recycler适配器:
When i ran the application in debug mode, i could see the getItemcount method size is increased, which means i am getting the data but it then produces the error above. The error above points to the getItem method which is null, This is my firestore recycler adapter:
public void populateMessageView(Query query){
FirestoreRecyclerOptions<Message> firestoreRecyclerOptions = new FirestoreRecyclerOptions.Builder<Message>()
.setQuery(query,Message.class)
.build();
recyclerAdapter = new FirestoreRecyclerAdapter<Message,RecyclerView.ViewHolder>(firestoreRecyclerOptions) {
@Override
protected void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position, @NonNull Message model) {
switch (holder.getItemViewType()) {
case VIEW_TYPE_MESSAGE_SENT:
((MeMessageHolder) holder).bind(model);
break;
case VIEW_TYPE_MESSAGE_RECEIVED:
((OtherMessageHolder) holder).bind(model);
}
}
@Override
public int getItemCount() {
return super.getItemCount();
}
@NonNull
@Override
public Message getItem(int position) {
return super.getItem(position);
}
@Override
public int getItemViewType(int position) {
Message message = getItem(position);
if(author.getId() == message.getAuthor().getId()){
return VIEW_TYPE_MESSAGE_SENT;
}
else return VIEW_TYPE_MESSAGE_RECEIVED;
//return super.getItemViewType(position);
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view;
if (viewType == VIEW_TYPE_MESSAGE_SENT) {
view = LayoutInflater.from(parent.getContext())
.inflate(R.layout.list_item_chat_me, parent, false);
return new MeMessageHolder(view);
} else if (viewType == VIEW_TYPE_MESSAGE_RECEIVED) {
view = LayoutInflater.from(parent.getContext())
.inflate(R.layout.list_item_chat_other, parent, false);
return new OtherMessageHolder(view);
}
return null;
}
@Override
public void onError(@NonNull FirebaseFirestoreException e) {
super.onError(e);
Log.d(TAG, e.getLocalizedMessage());
}
};
messagesList.setAdapter(recyclerAdapter);
recyclerAdapter.notifyDataSetChanged();
}
private class MeMessageHolder extends RecyclerView.ViewHolder{
private TextView messageBody, messageTime;
SimpleDateFormat simpleDateFormat ;
public MeMessageHolder(View itemView) {
super(itemView);
messageBody = findViewById(R.id.text_message_body_other);
messageTime = findViewById(R.id.text_message_time);
simpleDateFormat = new SimpleDateFormat("HH:mm", Locale.getDefault());
}
void bind (Message message){
messageBody.setText(message.getText());
messageTime.setText(simpleDateFormat.format(message.getTimestamp()));
}
}
private class OtherMessageHolder extends RecyclerView.ViewHolder{
private TextView messageBody,messageTime,messageName;
private ImageView otherMessageImage;
SimpleDateFormat simpleDateFormat;
public OtherMessageHolder(View itemView) {
super(itemView);
messageBody = findViewById(R.id.text_message_body_other);
messageTime = findViewById(R.id.text_message_time_other);
messageName = findViewById(R.id.text_message_name);
otherMessageImage = findViewById(R.id.image_message_profile);
simpleDateFormat = new SimpleDateFormat("HH:mm",Locale.getDefault());
}
void bind (Message message){
messageName.setText(message.getAuthor().getName());
messageBody.setText(message.getText());
messageTime.setText(simpleDateFormat.format(message.getTimestamp()));
}
}
我为此适配器使用了两个视口.
I am using two viewholders for this adapter.
推荐答案
我发现了导致此错误的两个问题...1.我的消息类没有默认的构造函数.2.我的观察者使用的是findviewbyid而不是itemview.findviewbyid ...基本上...错误是我的错误导致的..很高兴我发现了..
I figured out a couple of problems that was causing this error...1.my message class did not have a default constructor.2.my viewholders were using findviewbyid instead of itemview.findviewbyid...Basically...the error was as a result of my mistake..glad i figured it out..
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