Create string array from SQLite database column in Android Studio - arrays

Question

I have created an app with an SQLite database and a ListView that I want to populate using the database. To do this I have written an adapter class called HomeListAdapter. This class takes 4 string arrays as input and that is where my problem is. At first, I just used random string arrays to populate the ListView by typing them myself, for example:
String[] homelist_name_short = {
"Flower", "Bush", "Tree"};
String[] homelist_name_long = {
"Red rose", "Berry bush", "Oak"};
String[] homelist_date = {
"20-9-2017", "11-10-2017", "12-10-2017"};
String[] homelist_price = {
"€1.50", "€2.48", "€0.68"};
Now I want this to be put into the listview automatically and to do that I have written the code that can be seen below..
I have created a class called Home:
public class Home {
private String mShortHomeName;
private String mLongHomeName;
private String mHomeDate;
private String mHomePrice;
public Home(String ShortName, String LongName, String Date, String Price) {
this.mShortHomeName = ShortName;
this.mLongHomeName = LongName;
this.mHomeDate = Date;
this.mHomePrice = Price;
}
public String getShortName() {
return this.mShortHomeName;
}
public String getLongName() {
return this.mLongHomeName;
}
public String getDate() {
return this.mHomeDate;
}
public String getPrice() {
return this.mHomePrice;
}
}
Added the following to my DatabaseHelper:
public Cursor getAllHomesAsCursor() {
SQLiteDatabase db = this.getWritableDatabase();
String[] columns = {"rowid as _id","*"};
return db.query(TABLE_NAME,columns,null,null,null,null,null);
}
The following to the activity that contains my listview:
DatabaseHelper db = new DatabaseHelper(getActivity());
Cursor csr = db.getAllHomesAsCursor();
HLAdapter adapter = new HLAdapter(getActivity(), csr);
listView.setAdapter(adapter);
The HLAdapter looks as follows:
public class HLAdapter extends CursorAdapter {
public HLAdapter(Context context, Cursor cursor) {
super(context, cursor, 0);
}
#Override
public View newView(Context context, Cursor csr, ViewGroup parent) {
return LayoutInflater.from(context).inflate(
R.layout.homelist_listview_layout,
parent,
false
);
}
#Override
public void bindView(View view, Context context, Cursor csr) {
TextView sname = (TextView) view.findViewById(R.id.homelist_name_short);
TextView lname = (TextView) view.findViewById(R.id.homelist_name_long);
TextView date = (TextView) view.findViewById(R.id.homelist_date);
TextView price = (TextView) view.findViewById(R.id.homelist_price);
sname.setText(csr.getString(csr.getColumnIndex("name_short")));
lname.setText(csr.getString(csr.getColumnIndex("name_long")));
date.setText(csr.getString(csr.getColumnIndex("date")));
price.setText(csr.getString(csr.getColumnIndex("price")));
}
}
My DatabaseHelper class looks as follows:
public class DatabaseHelper extends SQLiteOpenHelper{
public static final String DATABASE_NAME = "Main.db";
public static final String TABLE_NAME = "current_table";
public static final String COL_1 = "name_short";
public static final String COL_2 = "name_long";
public static final String COL_3 = "date";
public static final String COL_4 = "price";
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, 1);
}
#Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table " + TABLE_NAME + " (name_short TEXT,name_long TEXT, due_date TEXT, price TEXT) ");
}
#Override
public void onUpgrade(SQLiteDatabase db, int i, int i1) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
public Cursor getAllHomesAsCursor() {
SQLiteDatabase db = this.getWritableDatabase();
String[] columns = {"rowid as _id","*"};
return db.query(TABLE_NAME,columns,null,null,null,null,null);
}
public boolean insertData(String name_short, String name_long, String due_date, String price) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(COL_1,name_short);
contentValues.put(COL_2,name_long);
contentValues.put(COL_3,due_date);
contentValues.put(COL_4,price);
long result = db.insert(TABLE_NAME,null,contentValues);
if(result == -1)
return false;
else
return true;
}
public void deleteAllData() {
SQLiteDatabase db = this.getWritableDatabase();
db.execSQL("DELETE FROM " + TABLE_NAME);
}
public Cursor getAllData() {
SQLiteDatabase db = this.getWritableDatabase();
Cursor res = db.rawQuery("SELECT * FROM " + TABLE_NAME ,null);
return res;
}
public Cursor getSpecifiedColumnData(String column) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor res = db.rawQuery("SELECT column FROM " + TABLE_NAME,null);
return res;
}
}
I would think that my code should be working fine, but when I run the app. It closes immediately. Can you tell me what the problem is?

Answer 1

I believe the issue is that you need 4 String arrays to be passed to the adapter, so doing it like above you'd need to have a unique equivalent of getAllData for each type.
However considering that a house has a short name, long name, date and price a better approach could to consider all of these properties as an object and thus create a class. You could then create a List not of String objects but as a List of House objects, you'd be able to get them all in one go etc.
So (P.S. for the sake of my sanity I've incorporated the SO4522191 into the following so I can keep some sort of track of the code) :-
1) Create your Home Object to hold all values/properties of a house:-
1-a) Create a file the same as your home name, it's going to be a java class file.
In this case I've called it SO45422191Home, the code could be along the lines of :-
public class SO45422191Home {
private String mShortHomeName;
private String mLongHomeName;
private String mHomeDate;
private String mHomePrice;
public SO45422191Home(String ShortName, String LongName, String Date, String Price) {
this.mShortHomeName = ShortName;
this.mLongHomeName = LongName;
this.mHomeDate = Date;
this.mHomePrice = Price;
}
public String getShortName() {
return this.mShortHomeName;
}
public String getLongName() {
return this.mLongHomeName;
}
public String getDate() {
return this.mHomeDate;
}
public String getPrice() {
return this.mHomePrice;
}
}
Explanation
Using the above we can create a SO45422191Home object, in code elsewhere e.g. in your activity, by using something
like SO45422191Home Myhome = new SO45422191Home("Flower","Red
Rose","20-9-2017","1.50");.
With the MyHome object you can extract the properties e.g.
MyHome.getPrice() would return a String with a value of 1.50.
Similar for the other properties.
You can create an array of objects e.g. SO45422191Home[] homes = new
SO45422191Home[3]; will create an array of 3 (empty) SO45422191Home
objects. We could set the first element of the array using homes[0] =
new SO45422191Home("Bush","Cherry","11-10-2017","2.48");
2) Create a means of getting an array of SO45422191Home objects from the database.
here's some code for this:-
public List<SO45422191Home> getAllHomes() {
List<SO45422191Home> rv = new ArrayList<>();
SQLiteDatabase db = this.getWritableDatabase();
Cursor csr = db.query(HOMETABLE,null,null,null,null,null,null);
while (csr.moveToNext()) {
SO45422191Home h = new SO45422191Home(
csr.getString(csr.getColumnIndex(SHORTHOMENAME)),
csr.getString(csr.getColumnIndex(LONGHOMENAME)),
csr.getString(csr.getColumnIndex(HOMEDATE)),
csr.getString(csr.getColumnIndex(HOMEPRICE))
);
rv.add(h);
}
csr.close();
return rv;
}
Explanation You used List and added elements to the list, List is similar but for SO45422191Home objects rather
than String objects.
The Database is opened, if not already open, using SQLiteDatabase db
= this.getWritableDatabase();.
All rows are extracted into a cursor.
The cursor is traversed each row at a time.
For each row a SO45422191Home object is created by getting the respective data from the cursor
(Note that csr.getColumnIndex(columnname) is used
rather than hard coding the column's index/offset, doing so can reduce
the chance for errors and also reduce overheads should changes be
applied.).
The the new object is added to the list.
Obviously column names would have to be adjusted, you may also want to add db.close() before the return.
3) Amend your adapter to take and use the the single list of objects rather than the 4 List.
here's an example adapter for use by a List (Note that R.layout.homeentry is the layout used for each entry in the ListView), the layout is below in the section re Cursor Adapter:-
public class AdapterHomeList2 extends ArrayAdapter {
List<SO45422191Home> homes;
LayoutInflater lInflater;
public AdapterHomeList2(Context context, List<SO45422191Home> homes) {
super(context,R.layout.homeentry, homes);
lInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
this.homes = homes;
}
#Override
public View getView(final int position, View convertView, final ViewGroup parent) {
View view = convertView;
if (view == null) {
view = lInflater.inflate(R.layout.homeentry, parent, false);
}
TextView sname = (TextView) view.findViewById(R.id.shortname);
TextView lname = (TextView) view.findViewById(R.id.longname);
TextView date = (TextView) view.findViewById(R.id.date);
TextView price = (TextView) view.findViewById(R.id.price);
sname.setText(homes.get(position).getShortName());
lname.setText(homes.get(position).getLongName());
date.setText(homes.get(position).getDate());
price.setText(homes.get(position).getPrice());
return view;
}
}
This is the code for an ArrayList :-
public class AdapterHomeList3 extends ArrayAdapter {
ArrayList<SO45422191Home> homes;
LayoutInflater lInflater;
public AdapterHomeList3(Context context, ArrayList<SO45422191Home> homes) {
super(context,R.layout.homeentry, homes);
lInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
this.homes = homes;
}
#Override
public View getView(final int position, View convertView, final ViewGroup parent) {
View view = convertView;
if (view == null) {
view = lInflater.inflate(R.layout.homeentry, parent, false);
}
TextView sname = (TextView) view.findViewById(R.id.shortname);
TextView lname = (TextView) view.findViewById(R.id.longname);
TextView date = (TextView) view.findViewById(R.id.date);
TextView price = (TextView) view.findViewById(R.id.price);
sname.setText(homes.get(position).getShortName());
lname.setText(homes.get(position).getLongName());
date.setText(homes.get(position).getDate());
price.setText(homes.get(position).getPrice());
return view;
}
}
Using a CursorAdapter
1) Add a new method to extract a cursor with all rows (NOTE! for cursor adapter a row named _id is required)
public Cursor getAllHomesAsCursor() {
SQLiteDatabase db = this.getWritableDatabase();
String[] columns = {"rowid as _id","*"};
return db.query(HOMETABLE,columns,null,null,null,null,null);
}
Note! instead of all columns i.e. coding null as the second parameter
to 'query' (which doesn't get the hidden rowid column (assuming
WITHOUT ROWID hasn't been used)), will will get the rowid (a unqiue
row identifier) and name this AS _id to suite the Cursor Adapter
hence "rowid as _id", the following * as the second element of
the columns array means all rows (specifying null as 2nd parameter
result in SELECT * .....).
Otherwise it's pretty simple. NOTE you must not close the database,
otherwise you can't access the cursor.
2) You will need a layout for each item in the list, as you would for a custom array adapter and it can be the same one i.e. there are no diferences according to which adapter is used. e.g. I created :-
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="#+id/shortname"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content" />
<TextView
android:id="#+id/longname"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content" />
<TextView
android:id="#+id/date"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content" />
<TextView
android:id="#+id/price"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content" />
</LinearLayout>
3) Create The Cursor Adpater as a class file, very similar to an Array Adapter.
public class AdapterHomeList extends CursorAdapter {
public AdapterHomeList(Context context, Cursor cursor) {
super(context, cursor,0);
}
#Override
public View newView(Context context, Cursor csr, ViewGroup parent) {
return LayoutInflater.from(context).inflate(
R.layout.homeentry, //<< layout for each list item
parent,
false
);
}
#Override
public void bindView(View view, Context context, Cursor csr) {
TextView sname = (TextView) view.findViewById(R.id.shortname);
TextView lname = (TextView) view.findViewById(R.id.longname);
TextView date = (TextView) view.findViewById(R.id.date);
TextView price = (TextView) view.findViewById(R.id.price);
sname.setText(csr.getString(csr.getColumnIndex(SO45422191.SHORTHOMENAME)));
lname.setText(csr.getString(csr.getColumnIndex(SO45422191.LONGHOMENAME)));
date.setText(csr.getString(csr.getColumnIndex(SO45422191.HOMEDATE)));
price.setText(csr.getString(csr.getColumnIndex(SO45422191.HOMEPRICE)));
}
}
Note! R.layout.homeentry being the layout for the list entries
and id's are from this.
4) From the respective activity, get the cursor, get an instance of the adapter and set the ListView to use the adapter.
e.g.:-
Cursor csr = dbhlp.getAllHomesAsCursor();
AdapterHomeList ahl = new AdapterHomeList(this,csr);
ListView hl = (ListView) this.findViewById(R.id.homelist);
hl.setAdapter(ahl);
result :-
Using cursor.getColumnIndex()
getColumnIndex
int getColumnIndex (String columnName)
Returns the zero-based index for the given column name, or -1 if the
column doesn't exist. If you expect the column to exist use
getColumnIndexOrThrow(String) instead, which will make the error more
clear.
SQLiteCursor
Using getColumnIndex as opposed to specifying the index removes the need to manually determine column offsets.
For example purposes, there is a table, named items with 3 columns, named as name, date and price :-
Using a query that uses the equivalent of SELECT * FROM items, the query will return a cursor with 3 columns, name, date and price
column name would have an offset of 0.
column date would have an offset of 1.
column price would have an offset of 2.
To extract the date from the cursor you could code cursor.getString(1);
However, if you were to have a query based upon SELECT date, price, name FROM items then the offsets would be:-
column name would have an offset of 2.
column date would have an offset of 0.
column price would have an offset of 1.
In this case you'd have to code cursor.getString(0); to extract the date.
It could be easy to inadvertently code the wrong offset, especially when using larger tables or when joining tables or when introducing generated columns.
Using cursor.getString(cursor.getColumnIndex("date")); could be used in both situations as it would return 1 in the first case and 0 in the second case.
Above, as an example, sname.setText(csr.getString(csr.getColumnIndex(SO45422191.SHORTHOMENAME))); has been coded.
Home.SHORTHOMENAME is a class varaible defined in the Database Helper (i.e. SO45422191 is the DatabaseHelper Class and SHORTHOMENAME is the class variable) that equates to the column name of the respective column as can be seen from the Database Helper code extract:-
public class SO45422191 extends SQLiteOpenHelper {
public static final String DBNAME = "SO45422191";
public static final String HOMETABLE = "homes";
public static final String SHORTHOMENAME = "shorthomename";
public static final String LONGHOMENAME = "longhomename";
public static final String HOMEDATE = "homedate";
public static final String HOMEPRICE = "homeprice";
// constructor
public SO45422191(Context context) {
super(context, DBNAME , null , 1);
}
#Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
sqLiteDatabase.execSQL("create table " + HOMETABLE +
"(" +
SHORTHOMENAME + " TEXT, " +
LONGHOMENAME + " TEXT, " +
HOMEDATE + " TEXT, " +
HOMEPRICE + ")");