I have two activities and two layouts. When I display the list in the first activity, everything works and gives me the number of the item in the list when clicked, but when I try to repeat the same thing in the second activity, it gives me that the RecyclerViewClickListener listener is null.
Adapter:
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
private ArrayList<String> array;
private RecyclerViewClickListener listener;
public MyAdapter( ArrayList<String> arrays, RecyclerViewClickListener listener)
{
this.listener = listener;
this.array = arrays;
}
@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_view,parent,false);
return new MyViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
holder.textView.setText(array.get(position));
}
@Override
public int getItemCount() {
return array.size();
}
public class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener{
public TextView textView;
public MyViewHolder(@NonNull View itemView) {
super(itemView);
textView = itemView.findViewById(R.id.text_card);
itemView.setOnClickListener(this);
System.out.println(itemView);
}
@Override
public void onClick(View v) {
System.out.println(listener);
System.out.println(v);
System.out.println(getAdapterPosition());
listener.onClick(v, getAdapterPosition());
}
}
public interface RecyclerViewClickListener{
void onClick(View v, int position);
}
}
first activity:
ArrayList<String> list_of_name= new ArrayList<>();
private RecyclerView recyclerView;
private MyAdapter.RecyclerViewClickListener listener;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.acticity1);
recyclerView = findViewById(R.id.recyclerView);
list();
}
public void list() {
MyAdapter myAdapter = new MyAdapter(list_of_name, listener);
recyclerView.setAdapter(myAdapter);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
listener = (v, position) -> {
itemPosition = list_of_name.get(position);
Syste.out.println(itemPosition );
};
}
Second activity:
private RecyclerView recyclerView;
private MyAdapter.RecyclerViewClickListener listener;
ArrayList<String> list2= new ArrayList<>();
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.acticity2);
recyclerView = findViewById(R.id.recyclerView1);
File internalStorageDir = getFilesDir();
File alice = new File(internalStorageDir, "file/");
for (File file : alice.listFiles()) {
list2.add(0, file.getName());
}
view();
}
public void view()
{
MyAdapter adapter = new MyAdapter(list2, listener);
recyclerView.setAdapter(adapter);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
listener = (v, position) -> {
itemPosition = list2.get(position);
Syste.out.println(itemPosition );
};
}
Error:
I/System.out: null
android.widget.LinearLayout{ecdf5a1 VFE...C.. ...P.... 0,0-1080,167}
0
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 28268
java.lang.NullPointerException: Attempt to invoke interface method 'void com.example.myapplication.recycler.MyAdapter$RecyclerViewClickListener.onClick(android.view.View, int)' on a null object reference
at com.example.myapplication.recycler.MyAdapter$MyViewHolder.onClick(MyAdapter.java:59)
at android.view.View.performClick(View.java:7185)
at android.view.View.performClickInternal(View.java:7162)
at android.view.View.access$3500(View.java:819)
at android.view.View$PerformClick.run(View.java:27684)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:224)
at android.app.ActivityThread.main(ActivityThread.java:7562)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
E/MQSEventManagerDelegate: failed to get MQSService.
I can’t understand why in the first case it processes the click normally, and in the second it says that the RecyclerViewClickListener is null
CodePudding user response:
public void list() {
MyAdapter myAdapter = new MyAdapter(list_of_name, listener);
recyclerView.setAdapter(myAdapter);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
listener = (v, position) -> {
itemPosition = list_of_name.get(position);
System.out.println(itemPosition );
};
}
This is where the issue is coming. You are passing the listener
first and then initialising it later. This is causing it to be null. Why don't you try this?:
public void list() {
listener = (v, position) -> {
itemPosition = list_of_name.get(position);
System.out.println(itemPosition );
};
MyAdapter myAdapter = new MyAdapter(list_of_name, listener);
recyclerView.setAdapter(myAdapter);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this);
}