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Creating a Java file to hold the database code
The first thing to do is create a Java file in your Android project that will house all the database-centric code. I am going to name my file
RemindersDbAdapter.java. The name RemindersDbAdapter was chosen because this is a simple implementation of the adapter software
engineering pattern.
The adapter pattern is simply a wrapper class that allows incompatible classes to communicate with each other. Think of the adapter pattern as the
wires and ports behind your television and DVD player. The cables plug into ports that are essentially adapters that allow devices to communicate that
normally couldn’t. They share a common interface. By creating an adapter to handle the database communication, you can communicate with this class
via the programming language of Java while this adapter class does the trans- lation and adapts certain Java requests into SQLite-specific commands.
Defining the key elements
Before you open and create your database, I need to define a few key fields. Type the code from Listing 12-1 into your RemindersDbAdapter class.
Listing 12-1: The Constants, Fields, and Constructors of the
RemindersDbAdapter
Class
private static final String DATABASE_NAME = “data”;
➝
1 private static final String DATABASE_TABLE = “reminders”;
➝
2 private static final int DATABASE_VERSION = 1;
➝
3 public static final String KEY_TITLE = “title”;
➝
5 public static final String KEY_BODY = “body”;
public static final String KEY_DATE_TIME = “reminder_date_time”; public static final String KEY_ROWID = “_id”;
➝
8 private DatabaseHelper mDbHelper;
➝
11 private SQLiteDatabase mDb;
➝
12 continued
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Listing 12-1 continued
private static final String DATABASE_CREATE =
➝
14 “create table “ + DATABASE_TABLE + “ “
+ KEY_ROWID + “ integer primary key autoincrement, “ + KEY_TITLE + “ text not null, “
+ KEY_BODY + “ text not null, “ + KEY_DATE_TIME + “ text not null;”;
private final Context mCtx;
➝
21 public RemindersDbAdapterContext ctx {
➝
23 this.mCtx = ctx;
}
Each line is explained in detail here:
➝
1 This is the physical name of the database that will exist in the
Android file system.
➝
2
This is the name of the database table that will hold the tasks. I cover the table and how to set it up in the SQL Table section
that follows.
➝
3 This is the version of the database. If you were to update the
schema of your database, you would increment this and pro- vide an implementation of the onUpgrade method of the
DatabaseHelper. I create the database helper in the “Creating the database table,” section later in this chapter.
➝
5 –
➝
8
These lines define the column names of the table that is described in the “Visualizing the SQL table” section that follows.
➝
11 This is the classwide DatabaseHelper instance variable. The
DatabaseHelper is an implementation of the SQLiteOpen- Helper class in Android. The SQLiteOpenHelper class helps
with the creation and version management of the SQLite database.
➝
12
This is the class-level instance of the SQLite database object that allows you to create, read, update, and delete records.
➝
14 This line defines the create script for the database. I’m concat-
enating the various values from the previous lines to create the various columns. Each component of the script is explained in
the “Visualizing the SQL table,” section that follows.
➝
21
This is the Context object that will be associated with the SQLite database object.
➝
23 The Context object is set via the constructor of the class.
The SQL database is now ready to be created with the DATABASE_CREATE script as defined previously.
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