I could't find IDs of fragment

Question

XML files

Here is the activity_main.xml file. that contains two fragments fragment_list.xml and fragment_deatails.xml

<androidx.fragment.app.FragmentContainerView
    android:id="@+id/fragmentContainerView"
    android:name="com.udemy.fragmentsapp.ListFrag"
    android:layout_width="0dp"
    android:layout_height="match_parent"
    android:layout_weight="1"
    tools:layout="@layout/fragment_list" />

<androidx.fragment.app.FragmentContainerView
    android:id="@+id/fram2"
    android:name="com.udemy.fragmentsapp.DetailFrag"
    android:layout_width="0dp"
    android:layout_height="match_parent"
    android:layout_weight="2"
    tools:layout="@layout/fragment_detail" />

---

Here is the fragment_list.xml file. that contain ListView

<ListView
    android:id="@+id/lvList"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

---

Here is the fragment_details.xml file. that contains one TextView

<TextView
    android:id="@+id/tvDescription"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/textview"
    android:layout_marginTop="20dp"
    android:layout_marginRight="20dp"
    android:layout_marginLeft="20dp"
    android:textSize="18dp"
    android:textStyle="bold"
    android:textColor="@color/black"/>

---

Java Files

Here is the ListFrag.java file.

ItemSelected activity;
public interface ItemSelected
{
    void onItemSelected(int index);
}
public ListFrag() {
    // Required empty public constructor
}

@Override
public void onAttach(@NonNull Context context) {
    super.onAttach(context);
    activity = (ItemSelected) context;
}

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    ArrayList<String> data = new ArrayList<>();
    for (int i = 1; i < 6; i++) {
        data.add(i + ". This is item " + i);
    }
    setListAdapter(new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1,data));
}

@Override
public void onListItemClick(@NonNull ListView l, @NonNull View v, int position, long id) {
    super.onListItemClick(l, v, position, id);
    activity.onItemSelected(position);
}

---

Here is the DeatailFrag.java file.

public DetailFrag(){
    super(R.layout.fragment_detail);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_detail, container, false);
}

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

}

@Override
public void onAttach(@NonNull Context context) {
    super.onAttach(context);

}

---

Here is the MainActivity.java file. when I want to access the ID "tvDescription" then it's showing ERROR: @layout/activity_main does not contain a declaration with id tvDescription.

Please help me. How can I access the ID? Tell me which one is the way to find IDs.

TextView tvDescription;
ArrayList<String> description;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    tvDescription = findViewById(R.id.tvDescription);

    for (int i = 1; i < 6; i++) {
        description.add("Description for item " + i);
    }
}
@Override
public void onItemSelected(int index) {
    tvDescription.setText(description.get(index));

}

---

Please run this code in your IDE.

Answer 1

The problem is that your activity and fragment are different classes. And although it is obvious that they represent a single view tree, in fact, in each component class, you should refer to the elements of only its layout.

Thus you need to use

TextView tvDescription = findViewById(R.id.tvDescription);

Directly in the DeatailFrag.onViewCreated after super.onViewCreated

And then, somehow pass the received value back to the activity, if necessary

Happy learning