How to query the database of another activity in one activity in Android?

Question

//First
case R.id.selectId:

        mmanager=(NotificationManager)this.getSystemService(NOTIFICATION_SERVICE);
        Intent intent=new Intent(this, AllSchool.class);
        PendingIntent pending=PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_CANCEL_CURRENT);
        Notification notification=new Notification.Builder(this)
                .setAutoCancel(true)
                .setTicker("下拉查看")
                .setSmallIcon(R.drawable.ic_launcher)
                .setContentTitle("学校")
                .setContentText("详细信息")
                .setContentIntent(pending)
                .build();
        mmanager.notify(1,notification);
        break;

//Second
protected void onCreate(Bundle savedInstanceState) {

    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.manager);
                    
    listViewId=(ListView)findViewById(R.id.listViewId);
    adapter=new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,contactList);
    listViewId.setAdapter(adapter);
    readManager();
    
}

public void readManager()
{
    SQLiteDatabase db2=msh.getWritableDatabase();
    Cursor cursor=db2.query("school", null, null, null, null, null, null);
    
    if(cursor.moveToFirst())
    {
        int id=cursor.getInt(cursor.getColumnIndex("id"));
        int phone=cursor.getInt(cursor.getColumnIndex("phone"));
        String name=cursor.getString(cursor.getColumnIndex("name"));
        String address=cursor.getString(cursor.getColumnIndex("address"));
        //Log.d("MainActivity","id is"+id);
        //Log.d("MainActivity","phone is"+phone);
        //Log.d("MainActivity","name is"+name);
        //Log.d("MainActivity","address is"+address);
        
        contactList.add(id+"\n"+phone+"\n"+name+"\n"+address);
        
        
    }

Error message Null pointer exception

Answer 1

First make sure there is a table 'school' in your database, then make sure this table has a field 'id''phone''name''address', and then make sure there is data in the table. You can judge after getting the cursor in the code If it is null, log it to see if it is null.