Добавление ListView в Fragment
Есть несколько вкладок Fragment при использовании BottomNavigationView.
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
tools:context=".ui.intents.IntentsFragment">
<TextView
android:id="@+id/text_visualtable"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:textAlignment="center"
android:textSize="20sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ListView
android:id="@+id/countriesList"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
При добавлении ListView в xml фрагмента и начальной инициализации в onCreate, приложение закрывается с ошибкой "Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference"
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;
import com.google.android.material.bottomnavigation.BottomNavigationView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
ArrayList<State> states = new ArrayList();
ListView countriesList;
StateAdapter stateAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
BottomNavigationView navView = findViewById(R.id.nav_view);
// Passing each menu ID as a set of Ids because each
// menu should be considered as top level destinations.
AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(
R.id.navigation_home, R.id.navigation_intents, R.id.navigation_addintent, R.id.navigation_notes, R.id.navigation_settings)
.build();
NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
NavigationUI.setupWithNavController(navView, navController);
// начальная инициализация списка
setInitialData();
// получаем элемент ListView
countriesList = (ListView) findViewById(R.id.countriesList);
// создаем адаптер
stateAdapter = new StateAdapter(this, R.layout.list_item, states);
// устанавливаем адаптер
countriesList.setAdapter(stateAdapter);
// слушатель выбора в списке
AdapterView.OnItemClickListener itemListener = new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
// получаем выбранный пункт
State selectedState = (State) parent.getItemAtPosition(position);
Toast.makeText(getApplicationContext(), "Был выбран пункт " + selectedState.getName(),
Toast.LENGTH_SHORT).show();
}
};
countriesList.setOnItemClickListener(itemListener);
}
private void setInitialData() {
states.add(new State("Бразилия", "Бразилиа", R.drawable.ic_home_black_24dp));
states.add(new State("Аргентина", "Буэнос-Айрес", R.drawable.ic_home_black_24dp));
states.add(new State("Колумбия", "Богота", R.drawable.ic_dashboard_black_24dp));
states.add(new State("Уругвай", "Монтевидео", R.drawable.ic_notifications_black_24dp));
states.add(new State("Чили", "Сантьяго", R.drawable.ic_notifications_black_24dp));
}
/* @Override
public void onBackPressed() {
super.onBackPressed();
overridePendingTransition(R.anim.opacity_in, R.anim.opacity_out);
}*/
}
Если добавлять ListView в activity_main.xml, а не в fragment_intents.xml приложение запускается и работает, но естественно ListView отображается при любой выбранной вкладке Fragment. Как добавить ListView в Fragment, чтобы данной ошибки не возникало?
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
tools:context=".ui.intents.IntentsFragment">
<TextView
android:id="@+id/text_visualtable"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:textAlignment="center"
android:textSize="20sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ListView
android:id="@+id/countriesList"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
package com.example.projectintent.ui.intents;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;
import com.example.projectintent.R;
public class IntentsFragment extends Fragment {
private IntentsViewModel intentsViewModel;
public View onCreateView(@NonNull LayoutInflater inflater,
ViewGroup container, Bundle savedInstanceState) {
intentsViewModel =
new ViewModelProvider(this).get(IntentsViewModel.class);
View root = inflater.inflate(R.layout.fragment_intents, container, false);
final TextView textView = root.findViewById(R.id.text_visualtable);
intentsViewModel.getText().observe(getViewLifecycleOwner(), new Observer<String>() {
@Override
public void onChanged(@Nullable String s) {
textView.setText(s);
}
});
return root;
}
}