![](/img/trans.png)
[英]Attempt to read from field 'android.view.View androidx.recyclerview.widget.RecyclerView$b0.a' on a null object reference
[英]Attempt to read from field 'android.view.View androidx.recyclerview.widget.RecyclerView$ViewHolder.itemView' on a null object reference
我正在制作一个从 sql 获取数据并将其放入回收视图的应用程序 我首先在列表视图中尝试了它,但我发现在回收视图中更容易 它基本上就像一个聊天系统应用程序,当我将我的数据添加到回收视图在 logcat 中给了我这个错误。
java.lang.NullPointerException: Attempt to read from field
'android.view.View
androidx.recyclerview.widget.RecyclerView$ViewHolder.itemView' on a
null object reference
at androidx.recyclerview.widget.RecyclerView$Adapter.createViewHolder(RecyclerView.java:7079)
at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6235)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6118)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6114)
at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2303)
at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1627)
at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1587)
at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:665)
at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4134)
at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3851)
at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
at android.view.View.layout(View.java:18010)
at android.view.ViewGroup.layout(ViewGroup.java:5817)
at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1080)
at android.view.View.layout(View.java:18010)
at android.view.ViewGroup.layout(ViewGroup.java:5817)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:344)
at android.widget.FrameLayout.onLayout(FrameLayout.java:281)
at android.view.View.layout(View.java:18010)
at android.view.ViewGroup.layout(ViewGroup.java:5817)
at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:444)
at android.view.View.layout(View.java:18010)
at android.view.ViewGroup.layout(ViewGroup.java:5817)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:344)
at android.widget.FrameLayout.onLayout(FrameLayout.java:281)
at android.view.View.layout(View.java:18010)
at android.view.ViewGroup.layout(ViewGroup.java:5817)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1742)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1585)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1494)
请帮忙,因为它没有给我任何关于错误来自何处或类似问题的线索。
这是我的适配器 class:
public class MyAppAdapter extends
RecyclerView.Adapter<MyAppAdapter.ViewHolder>//has a class viewholder which holds
{
private ArrayList<ClassListChat> mOriginalValues; // Original Values
private ArrayList<ClassListChat> mDisplayedValues;
public class ViewHolder extends RecyclerView.ViewHolder {
TextView messageText;
TextView messageUser;
TextView messageTime;
public ViewHolder(@NonNull View itemView) {
super(itemView);
}
}
public List <ClassListChat> parkingList;
public Context context;
ArrayList<ClassListChat> arraylist;
private MyAppAdapter(List<ClassListChat> apps, Context context) {
this.parkingList = apps;
this.context = context;
arraylist = new ArrayList<ClassListChat>();
arraylist.addAll(parkingList);
}
@Override
public MyAppAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,int viewType) {
View rowView = LayoutInflater.from(parent.getContext()).inflate(R.layout.listcontentstorechat,parent,false);
ViewHolder viewHolder = new ViewHolder(rowView);
if (rowView == null) {
LayoutInflater inflater = getLayoutInflater();
rowView = inflater.inflate(R.layout.listcontentstorechat, parent, false);
viewHolder.messageText = (BubbleTextView) rowView.findViewById(R.id.message_text);
viewHolder.messageUser = (TextView) rowView.findViewById(R.id.message_user);
viewHolder.messageTime = (TextView) rowView.findViewById(R.id.message_time);
rowView.setTag(viewHolder);
} else {
viewHolder = (ViewHolder) rowView.getTag();
}
// here setting up names and images
return viewHolder;
}
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
holder.messageText.setText(parkingList.get(position).getMessageText());
holder.messageUser.setText(parkingList.get(position).getMessageUser());
holder.messageTime.setText(DateFormat.format("dd-MM-yyyy (HH:mm:ss)", parkingList.get(position).getMessageTime()));
}
@Override
public int getItemCount() {
return itemArrayList.size();
}
}
I would really appreciate your hard work in helping me!!
编辑:现在它只给我一个空白的 bubbleTextView(我在我的应用程序中实现了它)但它不显示文本,也不显示时间,也不显示用户的任何想法?
这是我的 listcontentstorechat.xml:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_alignParentTop="true"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:id="@+id/message_user"
android:textStyle="normal|bold"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:layout_alignParentBottom="@+id/message_user"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:id="@+id/message_time"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<com.github.library.bubbleview.BubbleTextView
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_marginTop="5dp"
android:layout_below="@id/message_user"
android:textAppearance="@style/TextAppearance.AppCompat.Body1"
android:textColor="#FFF"
android:textSize="18sp"
android:id="@+id/message_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="10dp"
app:arrowWidth="8dp"
app:angle="8dp"
app:arrowHeight="10dp"
app:arrowPosition="14dp"
app:arrowLocation="left"
app:bubbleColor="#333639"
app:arrowCenter="true"
/>
</RelativeLayout>
这是我的 ClassListChat.java
public class ClassListChat {
public String messageText;
public String messageUser;
public long messageTime;
public ClassListChat(String messageText, String messageUser) {
this.messageText = messageText;
this.messageUser = messageUser;
messageTime = new Date().getTime();
}
public ClassListChat() {
}
public String getMessageText() {
return messageText;
}
public void setMessageText(String messageText) {
this.messageText = messageText;
}
public String getMessageUser() {
return messageUser;
}
public void setMessageUser(String messageUser) {
this.messageUser = messageUser;
}
public long getMessageTime() {
return messageTime;
}
public void setMessageTime(long messageTime) {
this.messageTime = messageTime;
}
EDIT2:经过一些改进后,它现在在 logcat 中返回一条错误消息:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.example.medicnes.ChatActivity$MyAppAdapter.onBindViewHolder(ChatActivity.java:275)
at com.example.medicnes.ChatActivity$MyAppAdapter.onBindViewHolder(ChatActivity.java:225)
at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7065)
at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7107)
at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6012)
at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6279)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6118)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6114)
onCreateViewHolder()
中的ViewHolder
始终不是 null,因为您在此方法中创建的View
不能是 null。
onCreateViewHolder()
的构建方式与用于创建ListView
适配器的getView()
不同
所以,请将您的onCreateViewHolder
更改为
@Override
public MyAppAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,int viewType) {
View rowView = LayoutInflater.from(parent.getContext()).inflate(R.layout.listcontentstorechat,parent,false);
ViewHolder viewHolder = new ViewHolder(rowView);
return viewHolder;
}
编辑:现在(实际上之前)它不会将文本添加到回收视图中有什么帮助吗? 我更新了我的问题
您从getItemCount()
返回错误的列表大小,因为您的适配器使用arraylist
作为其数据列表,因此您需要返回它的大小
所以把getItemCount()
改成
@Override
public int getItemCount() {
if (arraylist != null)
return arraylist.size();
else
return 0;
}
编辑 2:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.example.medicnes.ChatActivity$MyAppAdapter.onBindViewHolder(ChatActivity.java:275)
at com.example.medicnes.ChatActivity$MyAppAdapter.onBindViewHolder(ChatActivity.java:225)
at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7065)
at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7107)
at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6012)
at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6279)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6118)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6114)
您没有使用.findViewById()
初始化行项目布局中的视图,因此将ViewHolder
构造函数更改为
public ViewHolder(@NonNull View itemView) {
super(itemView);
messageText = itemView.findViewById(R.id.message_text);
messageUser = itemView.findViewById(R.id.message_user);
messageTime = itemView.findViewById(R.id.message_time);
}
您的适配器返回 null viewholders。
View rowView = LayoutInflater.from(parent.getContext()).inflate(R.layout.listcontentstorechat,parent,false);
rowView
在这里总是非空的,所以这个条件:
if (rowView == null) {
永远不会被击中,而是代码转到 else 分支
} else { viewHolder = (ViewHolder) rowView.getTag(); }
用viewHolder
替换 viewHolder 然后你返回它。
这部分代码看起来像是尝试将旧的 ListView 适配器改编为 RecyclerView 适配器。 对于 RecyclerView,您自己不需要setTag()
/ getTag()
。
只需创建并初始化您的视图持有者并从方法中返回它。
我遇到了同样的问题,当我尝试在Fragment
上使用recyclerView
从 firebase firestore 检索数据并将其放入recyclerView
时,我无法访问recyclerView
。 只需在 findViewById(R.id.recyclerViewid) 前面添加getView()
)
我之前的代码:
//Declared at the top of the class
RecylcerView recyclerView ;
//In the onViewCreate section
recyclerView = findViewById(R.id.recyclerview)//<--id of the recyclerView
我的代码之后:
//Declared at the top of the class
RecylcerView recyclerView ;
//In the onViewCreate section
recyclerView = (getView).findViewById(R.id.recyclerview)//<--id of the recyclerView
这可能是因为您没有通过 setcontentview 中的绑定返回视图
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.