当我单击删除按钮时，它将删除该孩子。删除子项后，其显示错误。有什么解决方案？我尝试了各种选择，但相同的问题一次又一次地显示。谁能帮我解决这个问题？
public class PostAdapter extends RecyclerView.Adapter<PostAdapter.ViewHolder> {
public Context mContext;
private List <Post>mPost;
private FirebaseUser firebaseUser;
ProgressBar progressBar;
public PostAdapter(Context mContext, List<Post> mPost) {
this.mContext = mContext;
this.mPost = mPost;
}
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view= LayoutInflater.from(mContext).inflate(R.layout.post_item,parent,false);
return new PostAdapter.ViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull final ViewHolder holder, final int position) {
firebaseUser= FirebaseAuth.getInstance().getCurrentUser();
final Post post=mPost.get(position);
try {
Glide.with(mContext.getApplicationContext()).load(post.getPostimage()).into(holder.post_image);
}catch (Exception e)
{
}
//holder.time.setText(post.getTime());
Get_Time_ago getTimeAgo=new Get_Time_ago();
long lastTime=Long.parseLong(String.valueOf(post.timestamp));
String last_seen_time=getTimeAgo.getTimeAgo(lastTime,mContext);
holder. time.setText(last_seen_time);
/*SimpleDateFormat sfd = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
String time=sfd.format(new Date(lastseenonline));
mLast_seenview.setText(time);*/
if(post.getDescription().equals("")){
holder.description.setVisibility(View.GONE);
}else {
holder.description.setVisibility(View.VISIBLE);
holder.description.setText(post.getDescription());
}
publisherInfo(holder.image_profile,holder.username,holder.blood,holder.publisher,post.getPublisher());
if(post.getPublisher().equals(firebaseUser.getUid())){
holder.delete.setVisibility(View.VISIBLE);
}else {
holder.delete.setVisibility(View.GONE);
}
holder.delete.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);
alertDialog.setTitle("Confirm Delete?");
alertDialog.setMessage("Do you want to delete your post?");
alertDialog.setPositiveButton("YES", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
FirebaseDatabase.getInstance().getReference("posts").child(post.getPostid()).removeValue();
notify();
}
});
alertDialog.setNegativeButton("NO", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
alertDialog.show();
}
});
}
@Override
public int getItemCount() {
return mPost.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
public ImageView image_profile,post_image,like,dislike,comment,save,delete;
public TextView username,blood,likes,dislikes,comments, description,publisher,time;
public ViewHolder(@NonNull View itemView) {
super(itemView);
image_profile=itemView.findViewById(R.id.image_profile);
post_image=itemView.findViewById(R.id.post_image);
like=itemView.findViewById(R.id.like);
comment=itemView.findViewById(R.id.comment);
save=itemView.findViewById(R.id.save);
delete=itemView.findViewById(R.id.delete);
username=itemView.findViewById(R.id.username);
blood=itemView.findViewById(R.id.blood);
time=itemView.findViewById(R.id.time);
likes=itemView.findViewById(R.id.likes);
dislikes=itemView.findViewById(R.id.dislikes);
dislike=itemView.findViewById(R.id.dislike);
comments=itemView.findViewById(R.id.comments);
description=itemView.findViewById(R.id.description);
publisher=itemView.findViewById(R.id.publisher);
progressBar = (ProgressBar) itemView.findViewById(R.id.progressBar);
}
}
private void publisherInfo (final ImageView image_profile, final TextView username,final TextView blood, final TextView publisher, final String userId ){
DatabaseReference reference= FirebaseDatabase.getInstance().getReference("Users").child(userId);
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
try {
User user=dataSnapshot.getValue(User.class);
Glide.with(mContext.getApplicationContext()).load(user.getImageurl()).into(image_profile);
username.setText(user.getUsername());
blood.setText(user.getBlood());
publisher.setText(user.getUsername());
}catch (Exception e){
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
}
错误
java.lang.NullPointerException: Attempt to read from field 'long com.example.mfree.Model.Post.timestamp' on a null object reference
at com.example.mfree.Adapter.PostAdapter.onBindViewHolder(PostAdapter.java:116)
at com.example.mfree.Adapter.PostAdapter.onBindViewHolder(PostAdapter.java:51)
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)
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.onMeasure(RecyclerView.java:3540)
at android.view.View.measure(View.java:23169)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.view.View.measure(View.java:23169)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:143)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1535)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:825)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:704)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1535)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:825)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:704)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at com.android.internal.policy.DecorView.onMeasure(DecorView.java:716)
at android.view.View.measure(View.java:23169)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2718)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1572)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1855)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1460)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7183)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
at android.view.Choreographer.doCallbacks(Choreographer.java:761)
2020-05-29 06:45:07.599 9312-9312/com.example.mfree E/AndroidRuntime: at android.view.Choreographer.doFrame(Choreographer.java:696)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
在setPositiveButton onClick：
代替此：
......
......
alertDialog.setPositiveButton("YES", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
FirebaseDatabase.getInstance().getReference("posts").child(post.getPostid()).removeValue();
notify();
............
尝试一下：
......
......
alertDialog.setPositiveButton("YES", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
FirebaseDatabase.getInstance().getReference("posts").child(post.getPostid()).removeValue();
mPost.remove(position);
notifyDataSetChanged();
............