NOTE:

NOTE: Of late, I have been getting requests for very trivial problems that many of you are facing in your day-to-day work. This blog is not to solve your "project" problems - surely not a "Support" site.
I just love to share my knowledge in my spare time and would appreciate any questions or feedback on the articles and code I have shared. I also do appreciate thought-provoking questions that would lead me to write more articles and share.
But please do not put your day-to-day trivial problems here. Even if you do, you most probably would not get a response here.
Thanks

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Friday, 18 February 2011

ListView of Data from SQLiteDatabase - Android

This is a next level tutorial where I am mixing two concepts – The ListView concept that is explicitly explained in the ListView Tutorial and the SQLiteDB concept in into own tutorial.

Here I am intending to query a database using a SQLiteDatabase API. The results I obtain are in a Cursor object that I iterate and create an ArrayList that is passed to the ListView. Let us see the steps involved in this exercise:

In the onCreate(…) method I have 2 methods corresponding to the two steps described above:

openAndQueryDatabase();
       
      displayResultList();

Let us see what each of them does:

Here is the first step:

private void openAndQueryDatabase() {
            try {
                  DBHelper dbHelper = new DBHelper(this.getApplicationContext());
                  newDB = dbHelper.getWritableDatabase();
                  Cursor c = newDB.rawQuery("SELECT FirstName, Age FROM " +
                        tableName +
                        " where Age > 10 LIMIT 4", null);

            if (c != null ) {
                  if  (c.moveToFirst()) {
                        do {
                              String firstName = c.getString(c.getColumnIndex("FirstName"));
                              int age = c.getInt(c.getColumnIndex("Age"));
                              results.add("Name: " + firstName + ",Age: " + age);
                        }while (c.moveToNext());
                  }
            }                
            } catch (SQLiteException se ) {
            Log.e(getClass().getSimpleName(), "Could not create or Open the database");
        } finally {
            if (newDB != null)
                  newDB.execSQL("DELETE FROM " + tableName);
                  newDB.close();
        }

      }       

Now, DBHelper is a class I have written extending the SQLiteOpenHelper class. All that it does is create a database by name “sample”, create a table within it and insert values into the table. It does this if the database does not already exist.  The table name is “Resource” and the columns in the table are Lastname, Firstname, Country, Age.

The code for this example can be downloaded here and you can look into the DBHelper code as well (which I do not want to elaborate here)

So, from the DBHelper class we get an open database which we call the newDB. Using this handle, we query the table for values. To keep it simple, while retrieving values I have hard-coded the column names which need not be the case. So I run a rawQuery and get the results into a Cursor.

Next I iterate through the Cursorand populate the results into an ArrayList of Strings “result”.  In the finally block, I not only close the database but before that I delete all the entries inserted into the database by the DBHelper class just to clean up.

Next how do I display the results in a ListView. If you know ListView– how it works it is rather simple. Else you could look at the ListViewTutorial. Here is the method:

      private void displayResultList() {
            TextView tView = new TextView(this);
        tView.setText("This data is retrieved from the database and only 4 " +
                  "of the results are displayed");
        getListView().addHeaderView(tView);
       
        setListAdapter(new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, results));
        getListView().setTextFilterEnabled(true);
           
      }

The only additional bit I have done here is to add a HeaderView (which is using the concept of programming UI explained in another tutorial).

I have written this tutorial based on some of the requests in my blog. Hope this helps.

Tuesday, 1 February 2011

Android Developers Blog: Android 3.0 Platform Preview and Updated SDK Tools

Android Developers Blog: Android 3.0 Platform Preview and Updated SDK Tools

Being in the domain of developing applications for large enterprises, what looks to me as interesting features of Android 3.0:
1. Enhancements for the Enterprise such as encrypted storage and password expiration!
2. And a UI Framework to suit larger screen devices.

Currently any enterprise that develops mobile applications has to duplicate its efforts towards developing and testing on each of the platforms like Android, Windows, Blackberry, iPhone etc. (Though I know there are a host of "write-once, deply on multi-platforms' options like AppMobi, Monotouch, Corona from Anscamobile, they need to mature a lot more). I hope this will help in consolidating development effort towards: "write once, run anywhere" for mobile devices.

I am looking at the Android market picking up rapidly and becoming the de-facto JVM equivalent in the mobile space...

How easy could life get with writing an app for one mobile and bingo! it works on all possible mobile devices that exist!! or at least majority of them! :)