What is making my app crash without an error - crash

Question

I am writing an app. that you can search info about celebs and save it to a SQlite database. I followed tutorials in showing the information but when I run the app it crashes without an error... please assist
When I request the data I only want the names display in a Listview, then when the user clicks on the name of the Celeb, it will open a page with all the saved data..I have no idea where to even start looking for the problem..I can open the app, save the data but when I open the activity to show the ListView it crashes without an error...
my xml for displaying the listview
<?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="wrap_content"
android:background="#drawable/mway"
android:orientation="vertical"
tools:context=".MainActivity">
<TextView
android:id="#+id/header"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="16dp"
android:background="#color/colorPrimaryDark"
android:text="#string/app_name"
android:textAlignment="center"
android:textColor="#color/colorPrimary"
android:textSize="32sp"
android:textStyle="bold"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ListView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="#+id/list_view"
android:background="#drawable/mway">
</ListView>
</LinearLayout>
Here is my java file for displaying the listview
import android.database.Cursor;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;
public class viewceleb extends AppCompatActivity {
DatabaseHelper db;
ArrayList<String> listItems;
ArrayAdapter adapter;
ListView userList;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_viewceleb);
userList = findViewById(R.id.list_view);
listItems = new ArrayList<>();
viewData();
userList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int i, long id) {
String text = userList.getItemAtPosition(i).toString();
Toast.makeText(viewceleb.this, "Now something can happen", Toast.LENGTH_LONG).show();
}
});
}
private void viewData() {
Cursor cursor = db.viewData();
if (cursor.getCount()== 0){
Toast.makeText(this,"No Data To Show", Toast.LENGTH_LONG).show();
}else {
while(cursor.moveToNext()){
listItems.add(cursor.getString(1));//index 1 is name, 0 is ID
}
adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, listItems);
userList.setAdapter(adapter);
}
}
}

Answer 1

You are only declaring db, it needs to be instantiated.
That is you have DatabaseHelper db; and you additionall need db = new DatabaseHelper(?); where ? are the parameters required by the DatabaseHelper constructor. Typically just the Context so perhaps db = new DatabaseHelper(this);. This would be coded in the activity's onCreate method BEFORE calling the viewData method.
e.g.
public class viewceleb extends AppCompatActivity {
DatabaseHelper db;
ArrayList<String> listItems;
ArrayAdapter adapter;
ListView userList;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_viewceleb);
dn = new DatabaseHelper(this); //<<<<<<<<<< ADDED note just the context has been assumed, the parameters depend upon the constructor as per what is coded in the DatabaseHelper class.
userList = findViewById(R.id.list_view);
listItems = new ArrayList<>();
viewData();
userList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int i, long id) {
String text = userList.getItemAtPosition(i).toString();
Toast.makeText(viewceleb.this, "Now something can happen", Toast.LENGTH_LONG).show();
}
});
}
private void viewData() {
Cursor cursor = db.viewData();
if (cursor.getCount()== 0){
Toast.makeText(this,"No Data To Show", Toast.LENGTH_LONG).show();
}else {
while(cursor.moveToNext()){
listItems.add(cursor.getString(1));//index 1 is name, 0 is ID
}
adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, listItems);
userList.setAdapter(adapter);
}
}
}