CODEWITHSUNDEEP
javaandroidfunctionandroid-activitystatic
Magnus
Magnus

Reputation: 370

Calling function from another activity

I have an activity that contains all the functions for controlling my database, and I want all other activities to use to these functions when interacting with the database. Below is an example of my problem.

Clock script:

public class Clock extends Activity
{
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_clock);

        Data.createTable(); //<<<
    }
        //...
}

Data script:

public class Data extends Activity
{
    SQLiteDatabase mydb;
    private static String DBNAME = "SHIFTS.db";
    private static String TABLE = "MY_SHIFTS"; 

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_data);
    }   

    public void createTable() //<<<
    {
        try
        {
            mydb = openOrCreateDatabase(DBNAME, Context.MODE_PRIVATE,null);
            mydb.execSQL("CREATE TABLE IF  NOT EXISTS "+ TABLE +" (ID INTEGER PRIMARY KEY, STARTDATE TEXT, ENDDATE TEXT, LENGTH INTEGER, TYPE INTEGER);");
            mydb.close();
        }
        catch(Exception e)
        {
            Toast.makeText(getApplicationContext(), "Error in creating table", Toast.LENGTH_LONG).show();
        }
    }
    // ... lots more functions
}

Error message:

Cannot make a static reference to the non-static method createTable() from the type Data.

And when I trying to make method static, it just causes more problems.

Also if I try Data data = new Data(); data.createTable(); I get a NullPointerException.

What is the problem here?

Upvotes: 4

Views: 49145

Answers (4)

user3507760
user3507760

Reputation: 11

i was following this question and based on the answer by Android_Dev i made changes to my code as below

1st class

 class blah extends activity {
 //// onCreate , initialization etc here

     public void sss(context c)
   {

    Toast(c , "text" , toast.LENTGH_LONG) ;

   }

  }

2nd Class

public xxxx extends activity
{

Context c = getApplicationContext();
blah b = new blah(this) ;

 /// inside an onclicklistener attached to a button object, i put this
    b.sss(c) ; 

}

I have not included all other stuff usually found in classes extending Activity class since i just wanted to show what i did to call function from other class. This solution was perfect for me. May or may not be useful for others though

Upvotes: -1

Phant&#244;maxx
Phant&#244;maxx

Reputation: 38098

Add the static keyword to your shared methods

public static void createTable()

Then use:

Data.createTable();

somewhere in another Class / Fragment / Activity.

I do so and it works.

Well, my "Data" is a normal Class, not an Activity, but I also have an Activity with shared methods in the very same way.

This is my dbTableCreate method:

// Create the database table if it doesn't exist
protected final static void dbTableCreate(final Context ctx)
{
    SQLiteDatabase db = null;
    try
    {
        db = ctx.openOrCreateDatabase(DB_NAME, Context.MODE_PRIVATE, null);
        db.execSQL
        (
            "CREATE TABLE IF NOT EXISTS " + DB_TABLE +
            " (date DATETIME PRIMARY KEY NOT NULL DEFAULT (CURRENT_DATE), " +
            "score INTEGER DEFAULT (null));"
        );
    }
    catch (final SQLiteException se)
    {
        System.out.println
        (
            ctx.getClass().getSimpleName() + "\n" +
                "Could not create the database"
        );
        se.printStackTrace();
    }
    finally
    {
        db.close();
    }
}

And I call it like:

Context ctx = getApplicationContext();
CLS_DB.dbTableCreate(ctx);

The main difference between my class and yours is that mine is declared as

public final class CLS_DB
{
    /* ----------------------------- Constants ------------------------------ */

    private final static String DB_NAME = "pat.db";
    private final static String DB_TABLE = "tests";

    /* ------------------------------ Methods ------------------------------- */

And not as an Activity.
I'm not initializing the Class, and it has no constructor.
It's just a bin of shared (and not, for doing operations not seen anywhere else in my code) methods.

Upvotes: 13

Swapnil
Swapnil

Reputation: 2512

Best way with java standard is make Singleton class Database.Put all these shared methods in this class.All activities in your application will perform database operations using this Singleton class.

Upvotes: 0

user3151973
user3151973

Reputation: 86

I would have all DB related methods in a singleton http://en.wikipedia.org/wiki/Singleton_pattern. I would send the context to that singleton, or just static methods.

I don't thnk its a good idea to have an activity as a database manager.

Upvotes: 2

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