android - 尝试在空对象引用上调用接口方法“____”
问题描述
所以实际上我试图从我的适配器启动一个方法到我的一个片段我也将一个变量从适配器传递到那个片段，方法是我创建了一个作业接口但不幸的是，不确定有一个空指针异常问题出在哪里，请查看我的代码并让我知道错误在哪里
适配器
public class UserAdapter extends RecyclerView.Adapter<UserAdapter.ViewHolder> {
private Context mContext;
private List<User> mUsers;
private boolean isChat;
private boolean isBlock;
private boolean isAdd;
private boolean isGroup;
private boolean checked;
private final boolean unreadbool = true;
private GroupMethods listener;
String currentgroup;
String theLastMessage;
String UnreadMessage;
public UserAdapter(Context mContext, List<User> mUsers, boolean isChat, boolean isAdd, boolean isBlock, boolean isGroup) {
this.mUsers = mUsers;
this.mContext = mContext;
this.isChat = isChat;
this.isAdd = isAdd;
this.isBlock = isBlock;
this.isGroup = isGroup;
}
public UserAdapter(GroupMethods listener){
this.listener = listener;
}
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
ViewGroup viewGroup = (ViewGroup) LayoutInflater.from(mContext).inflate(R.layout.user_item, parent, false);
return new UserAdapter.ViewHolder(viewGroup);
}
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
final User user = mUsers.get(position);
holder.UsernameText.setText(user.getUsername());
holder.dt.setText(user.getDt());
if (user.getImageUrl().equals("default")) {
holder.profile.setImageResource(R.drawable.user);
} else {
Glide.with(mContext).load(user.getImageUrl()).into(holder.profile);
}
if (unreadbool) {
UnreadMessage(user.getId(), holder.unread);
}
if(isGroup){
holder.addpart.setVisibility(View.VISIBLE);
final String addpart = user.getId();
holder.addpart.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
if(isChecked){
addPart_group(addpart); //This is initiating the interface and error comes here
}else {
//Do Nothing
}
}
});
}
if(!isGroup){
holder.addpart.setVisibility(View.GONE);
}
private void addPart_group(String id) {
listener.AddParticipant(id); //And here's its passing and initiating
}
@Override
public int getItemCount() {
return mUsers.size();
}
public static class ViewHolder extends RecyclerView.ViewHolder {
public TextView UsernameText = itemView.findViewById(R.id.username);
public TextView dt = itemView.findViewById(R.id.dt);
public ImageView profile;
private final CheckBox addpart;
private final ImageView img_on;
private final ImageView img_off;
private final ImageView unread;
private final TextView last_msg;
private final ImageView UnBlock_btn;
public ViewHolder(View view) {
super(view);
profile = itemView.findViewById(R.id.profile_image);
img_on = itemView.findViewById(R.id.img_on);
img_off = itemView.findViewById(R.id.img_off);
last_msg = itemView.findViewById(R.id.last_msg);
unread = itemView.findViewById(R.id.unread);
UnBlock_btn = itemView.findViewById(R.id.cancel_button);
addpart = itemView.findViewById(R.id.addpart);
}
}
日志猫
java.lang.NullPointerException: Attempt to invoke interface method 'void
com.margsapp.messenger.groupclass.GroupMethods.AddParticipant(java.lang.String)' on a null object reference
at com.margsapp.messenger.Adapter.UserAdapter.addPart_group(UserAdapter.java:234)
at com.margsapp.messenger.Adapter.UserAdapter.access$200(UserAdapter.java:37)
at com.margsapp.messenger.Adapter.UserAdapter$2.onCheckedChanged(UserAdapter.java:152)
at android.widget.CompoundButton.setChecked(CompoundButton.java:180)
at android.widget.CompoundButton.toggle(CompoundButton.java:135)
at android.widget.CompoundButton.performClick(CompoundButton.java:140)
at android.view.View.performClickInternal(View.java:7102)
at android.view.View.access$3500(View.java:801)
at android.view.View$PerformClick.run(View.java:27336)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
有关更多详细信息，这里是该方法所在的片段
public class AddParticipantsFragment extends Fragment implements GroupMethods {
private RecyclerView recyclerView;
private List<User> mUsers;
DatabaseReference databaseReference;
FirebaseUser firebaseUser;
private List<Chatlist>usersList;
private UserAdapter userAdapter;
public String groupId;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_add_participants, container, false);
recyclerView = view.findViewById(R.id.recycler_view);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
usersList = new ArrayList<>();
UserAdapter userAdapter = new UserAdapter(this);//Initializing here
firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
databaseReference = FirebaseDatabase.getInstance().getReference("Chatlist").child(firebaseUser.getUid());
databaseReference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
usersList.clear();
for(DataSnapshot snapshot1 : snapshot.getChildren()){
Chatlist chatlist = snapshot1.getValue(Chatlist.class);
usersList.add(chatlist);
}
chatList();
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
}
});
AddParticipants activity = (AddParticipants) getActivity();
assert activity != null;
groupId = activity.getMyData();
return view;
}
private void chatList() {
mUsers = new ArrayList<>();
databaseReference = FirebaseDatabase.getInstance().getReference("Users");
databaseReference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
mUsers.clear();
for (DataSnapshot snapshot1 : snapshot.getChildren()){
User user = snapshot1.getValue(User.class);
for (Chatlist chatlist : usersList){
assert user != null;
if(user.getId().equals(chatlist.getId())){
if(chatlist.getFriends().equals("Messaged")){
mUsers.add(user);
}if (chatlist.getFriends().equals("Requested")){
//DoNothing
}
if(chatlist.getFriends().equals("Blocked")){
//Dont do anything
}
}
}
}
userAdapter = new UserAdapter(getContext(), mUsers, false, false, false, true);
recyclerView.setAdapter(userAdapter);
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
}
});
}
@Override
public void AddParticipant(String id) {
DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("Grouplist").child(groupId);
HashMap<String, String> hashMap1 = new HashMap<>();
hashMap1.put("id", id);
hashMap1.put("admin","false");
databaseReference.setValue(hashMap1);
}
}
这是界面
public interface GroupMethods {
public void AddParticipant(String id);
}
解决方案
你是如何创建这个适配器的？适配器有两种不同的构造方法，一种包含许多参数，另一种只包含侦听器。
如果您需要对该适配器的所有使用访问它并删除第二个构造函数，则应将侦听器作为另一个参数包含在第一个构造函数中，否则使用任何一个构造函数都会使适配器处于不完整状态。
如果不是所有适配器的使用都需要包含监听器，那么创建一个单独的方法而不是一个单独的构造函数来将监听器分配给适配器类。
public setAdapter(GroupMethods listener){
this.listener = listener;
}
此外，您的 RecyclerView 没有从 RecyclerView.Adapter 扩展，因为它可能应该，检查RecyclerView 文档中可用的示例
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