I am attempting to learn Android Studios using the free Udemy course "Learn Android Application Development." I am on lesson 44 "Fragments Part 1." I am unable to get through the lesson because of an error. I have spent two days and ~8 hours trying to figure it out. Please help me!
The goal of the lesson is to create an app that has a list on one side of the screen and the details on the other. When the user clicks one of the list items, the details are displayed on a textview on the other side of the screen.
The instructor guides us through creating two fragments (ListFrag and DetailFrag) and adding them to the main activity side-by-side. He goes through setting up the list fragment (ListFrag) and passing the clicked list item's index to the main activity. All of that works.
DetailFrag contains a TextView (tvDescription). The instructor sets up the textview and changes the value from the main activity using the index from ListFrag. When running the app, it crashes when you click a list item.
There is one error - '@layout/activity_main' does not contain a declaration with id 'tvDescription'. The issue is in MainActivity.java, tvDescriptions = findViewById(R.id.tvDescription);.
Please help. Thanks in advance for your replies.
XML Files:
activity_main.xml
?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
tools:context=".MainActivity">
<androidx.fragment.app.FragmentContainerView
android:id="@+id/listFrag"
android:name="com.example.fragmentvideorev2.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/detailFrag"
android:name="com.example.fragmentvideorev2.DetailFrag"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="2"
tools:layout="@layout/fragment_detail" />
</LinearLayout>
fragment_list.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".ListFrag">
<ListView
android:id="@+id/lvList"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
fragment_detail.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:background="@color/teal_700"
tools:context=".DetailFrag">
<TextView
android:id="@+id/tvDescription"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:layout_marginRight="20dp"
android:text="TextView"
android:textColor="#FFFFFF"
android:textSize="18sp" />
</LinearLayout>
Java Files:
MainActivity.java
package com.example.fragmentvideorev2;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import android.os.Bundle;
import android.widget.TextView;
import java.lang.reflect.Array;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity implements ListFrag.ItemSelected {
TextView tvDescriptions;
ArrayList<String> descriptions;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tvDescriptions = findViewById(R.id.tvDescription);
ArrayList<String> descriptions = new ArrayList<String>();
descriptions.add("Description for item 1");
descriptions.add("Description for item 2");
descriptions.add("Description for item 3");
}
@Override
public void onItemSelected(int index) {
tvDescriptions.setText(descriptions.get(index));
}
}
ListFrag.java
package com.example.fragmentvideorev2;
import android.content.Context;
import android.os.Bundle;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.ListFragment;
import androidx.lifecycle.LifecycleObserver;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import java.util.ArrayList;
public class ListFrag extends ListFragment {
ItemSelected activity;
public interface ItemSelected
{
void onItemSelected(int index);
}
public ListFrag() {
// Required empty public constructor
}
//called when frag associated with activity, context is activity
@Override
public void onAttach(@NonNull Context context) {
super.onAttach(context);
activity = (ItemSelected) context;
}
//called when oncreate is finished
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
ArrayList<String> data = new ArrayList<String>();
data.add("1. This is one");
data.add("2. This is two");
data.add("3. This is three");
setListAdapter(new ArrayAdapter<String>(getActivity(), android.R.layout.simple_expandable_list_item_1, data));
}
//value list get clicked, know posiiton
@Override
public void onListItemClick(@NonNull ListView l, @NonNull View v, int position, long id) {
activity.onItemSelected(position);
}
}
DetailFrag.java - unchanged after creation
package com.example.fragmentvideorev2;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.fragment.app.Fragment;
import org.w3c.dom.Text;
public class DetailFrag extends Fragment {
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
public DetailFrag() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment DetailFrag.
*/
// TODO: Rename and change types and number of parameters
public static DetailFrag newInstance(String param1, String param2) {
DetailFrag fragment = new DetailFrag();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@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);
}
}
