SQLite DB Example Android Developer Tutorial Part 12

There are 4 ways of storing data on the android platform:

• 1.    Preferences
• 2.    SQLite Database
• 3.    Files
• 4.    Network

A word about each of them here and then I will move on to an example that shows how to work with SQLite DB that comes along with the android platform.

Preferences–

Basically used for storing user preferences for a single application or across applications for a mobile. This is typically name-value pairs accessible to the context.

Databases –

Android supports creating of databases based on SQLite db. Each database is private to the applications that creates it

Files –

Files can be directly stored on the mobile or on to an extended storage medium. By default other applications cannot access it.

Network –

Data can be stored and retrieved from the network too depending on the availability.

If an application wants to store and retrieve data for its own use, without having to share the data across applications, it can access the SQLite DB directly. There is no need of a content provider. We have seen in an earlier post how to use content providers.

In this example, we will do the following:

1.    Create a database (typically a one time activity)

2.    Create a table (typically a one time activity)

3.    Insert values into the table

4.    Retrieve the values from the table

5.    Display the retrieved values as a List view

6.    Delete all the records from the table before closing the connection to the database

Step 1: Create a database:

   sampleDB =  this.openOrCreateDatabase(SAMPLE_DB_NAME, MODE_PRIVATE, null);

This opens a database defined in the constant SAMPLE_DB_NAME, if it already exists. Else it creates a database and opens it. The second parameter is operating mode : MODE_PRIVATE meaning it is accessible to only this context. The other modes are and MODE_WORLD_WRITABLE. MODE_WORLD_READABLE

Step 2: Create a Table:

sampleDB.execSQL("CREATE TABLE IF NOT EXISTS " +

                        SAMPLE_TABLE_NAME +

                        " (LastName VARCHAR, FirstName VARCHAR," +

                        " Country VARCHAR, Age INT(3));");

Step 3: Insert values into the table:

sampleDB.execSQL("INSERT INTO " +

                        SAMPLE_TABLE_NAME +

                        " Values (Makam,Sai Geetha,India,25);");

Step 4: Retrieve values

Cursor c = sampleDB.rawQuery("SELECT FirstName, Age FROM " +

                        SAMPLE_TABLE_NAME +

                        " where Age > 10 LIMIT 5", null);

           

      if (c != null ) {

            if  (c.moveToFirst()) {

                  do {

String firstName = c.getString(c.getColumnIndex("FirstName"));

                  int age = c.getInt(c.getColumnIndex("Age"));

                  results.add("" + firstName + ",Age: " + age);

                  }while (c.moveToNext());

            }

       }

Step 5: Display the values as a list

           

       this.setListAdapter(newArrayAdapter<String>(this, android.R.layout.simple_list_item_1,results));

The statement displays it as a list as the class extends a ListActivity.

Step 6: Delete the values from the table in the finally part of the try block

finally {

            if (sampleDB != null)

                  sampleDB.execSQL("DELETE FROM " + SAMPLE_TABLE_NAME);

                  sampleDB.close();

        }

It is as simple as this to work with the SQLite DB even in android. No different from a desktop application. However, there are various overloaded methods of query() provided by the SQLIteDatabase class which can be more optimally used instead of execSQL.

The complete code for this example is downloadable here.

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Android UI – Inflate from XML Dynamic UI Creation

We have seen that we can declare User Interface in Android through XML or we can even create the UI Programmatically. Now, we will see how we can mix the two and use it for building dynamic User Interfaces. One example of such a case would be when on a particular action of the user on one of the UI elements, you need more UI elements to appear on the same screen. How do we achieve this?

You can do it in two ways:

1.       The dynamic part of the UI can be created programmatically. However we saw in my earlier tutorial that it is not a very good way to mix UI and code.  So, we can

2.       Define the dynamic UI too as an XML and use XML inflation to include it into the existing UI.

We will see how to do the 2^ndway, which probably is a good practice too.

As always, again a very simple example. Assume I have a very simple linear layout. In that I want to include a button. I can do it as part of the mail XML itself. However, assume that this button is supposed to be reused in many activities and hence I have defined it as a separate XML. How do I include it into the main XML?

So, here is the main.xml

<?xml version="1.0"encoding="utf-8"?>

<LinearLayout >="http://schemas.android.com/apk/res/android"

    android:orientation="vertical"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:id="@+id/layout1"

    >

</LinearLayout>

Here is the buttons.xml that is also created in the res/layout folder:

<?xml version="1.0"encoding="utf-8"?>

<Button >="http://schemas.android.com/apk/res/android"

        android:id="@+id/button_small_left"

 style="?android:attr/buttonStyleSmall"

        android:text="Press to close"

    android:layout_width="wrap_content"

    android:layout_height="wrap_content"/>

And here is the Activity’s onCreate(…) method of the InflateView class:

    public voidonCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        final LayoutInflater  inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        Button b = (Button)inflater.inflate(R.layout.buttons,

                null);

       

        lLayout = (LinearLayout)findViewById(R.id.layout1);

        lLayout.addView(b);

First 3 lines must be familiar. In the 4^thline, I am getting a handle to the LayoutInflater through the getSystemService(…) method.  This inflater has a method inflate to which I pass the buttons.xml by passing the parameter R.layout.buttons. Then, I try to append this button to the Linear Layout that already exists and is set as the view in line 2 setContentView(R.layout.main). How to append? I get a handle to the LinearLayoutlLayout and add the new button to it in the last line!

That simple to inflate an XML and append it to an existing view!

However, I have gone ahead and added another bit to this program as shown below:

        b.setOnClickListener(new OnClickListener() {

           

            public void onClick(View v) {

                  //restrict to adding only 1 textview child element

                  if (lLayout.getChildAt(2) == null)

                  {

                  TextView tv = (TextView)inflater.inflate(R.layout.text, null);

                  lLayout.addView(tv);

                  }

            }

        });

On the click of this dynamically added button, I am showing how we can add more to the UI dynamically through inflation. Assume, on the click of the button, you want to show some new text. This TextView is defined in another XML called text.xml which is also in the res/layout folder.

So, I am inflating from this XML and appending it to the LinearLayout view. So, a lot can be achieved for dynamic UI through inflation.

You can download the complete sample code here.

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