Fragments

Fragments are very useful in modularizing the code and UI. Fragment's use increases reusability in the project.

In this tutorial:

1.  How to use fragments with activity.

2.  Getting click events in the activity from fragments.

3.  Passing data from activity to fragments and fragments to fragments.

4.  Replacing fragments from activity and from fragment to fragment.

Note:

Here we will create one activity MainActivity and 3 fragments MainFragment, InputFragment, DetailFragment.

We will take some input from user in one fragments and will show the entered values in another fragments.

Let's start:

1.  Create a android project.

2.  Create a MainActivity.

MainActivity.java

public class MainActivity extends FragmentActivity implements ActivityListener{

    /** Called when the activity is first created.

     *  ActivityListener is the interface which is used

     *  to get callback from fragment.

     */

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        //Fragments are added programmatically here...

        MainFragment fragment = new MainFragment();

        FragmentManager fragmentManager = getSupportFragmentManager();

        FragmentTransaction transaction = fragmentManager.beginTransaction();

        transaction.add(R.id.frameLayout, fragment);

        transaction.commit();

    }

    public void getData(Bundle bundle) {

        if ( bundle != null ) {

            FragmentManager fragmentManager = getSupportFragmentManager();

            DetailFragment detailFragment = new DetailFragment();

            detailFragment.setArguments(bundle);

            FragmentTransaction transaction = fragmentManager.beginTransaction();

            transaction.replace(R.id.frameLayout, detailFragment);

            transaction.commit();

        }

    }

}

main.xml

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

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:orientation="vertical"

    android:id="@+id/frameLayout" >

</FrameLayout>

Note: To add fragments inside xml:

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

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:orientation="vertical"

    android:id="@+id/frameLayout" >

<fragment 

  android:name="com.fragmentdemo.fragment.MainFragment"
  android:id="@+id/fragment"
  android:layout_weight="1"
  android:layout_width="0dp"
  android:layout_height="fill_parent" />

</FrameLayout>

3.  Create MainFragment.

MainFragment.java

public class MainFragment extends Fragment{

    private Button mInput;

   /**

     * Define Click listener for the button.

     */

    private OnClickListener inputClickListener = new OnClickListener() {

        public void onClick(View v) {

            FragmentManager fragmentManager = getFragmentManager();

            InputFragment inputFragment = new InputFragment();

            FragmentTransaction transaction = fragmentManager.beginTransaction();

            transaction.replace(R.id.frameLayout, inputFragment);

            transaction.addToBackStack(null);

            transaction.commit();

        }

    };

    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container,

            Bundle savedInstanceState) {

        View contentView = inflater.inflate(R.layout.main_frag, null);

        contentView.setDrawingCacheEnabled(false);

        mInput = (Button)contentView.findViewById(R.id.btnInput);

        return contentView;

    }

    @Override

    public void onStart() {

        super.onStart();

        mInput.setOnClickListener(inputClickListener);

    }

}

main_frag.xml

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

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

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:gravity="center"

    android:orientation="vertical" >

    <Button

        android:id="@+id/btnInput"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:text="Add User Details"

        android:textSize="20dp" />

</LinearLayout>

4.  Create InputFragment.

InputFragment.java

public class InputFragment extends Fragment{

    private ActivityListener mListener;

    private Button mSubmit;

    private EditText mName, mOccupation, mDesignation;

    private OnClickListener submitClickListener = new OnClickListener() {

        public void onClick(View v) {

            if (mName.getText().toString().trim().length() == 0|| mOccupation.getText().toString().trim().length() == 0 || mDesignation.getText().toString().trim().length() == 0 ) {

            Toast.makeText( getActivity(), "Field can not be left empty.", Toast.LENGTH_SHORT).show();

            }

            else {

                Bundle bundle = new Bundle();

                bundle.putString("name", mName.getText().toString());

                bundle.putString("occupation", mOccupation.getText().toString());

                bundle.putString("designation", mDesignation.getText().toString());

        //Method1: Pass data to activity and then to fragment.

                if ( mListener != null )

                    mListener.getData(bundle);

        //Method2: pass data to fragment directly.

        FragmentManager fragmentManager = getFragmentManager();

        DetailFragment detailFragment = new DetailFragment();

        detailFragment.setArguments(bundle);

        FragmentTransaction transaction = fragmentManager.beginTransaction();

                transaction.replace(R.id.frameLayout, detailFragment);

        transaction.remove(InputFragment.this);

        transaction.commit();

            }

        }

    };

    //Check for interface if activity has implemented it or not.

    @Override

    public void onAttach(Activity activity) {

        // TODO Auto-generated method stub

        super.onAttach(activity);

        try {

            mListener = (ActivityListener)activity;

        }catch (ClassCastException e) {

            Toast.makeText( activity, "Activity must implement this interface.", Toast.LENGTH_SHORT).show();

        }

    }

    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container,

            Bundle savedInstanceState) {

        View contentView = inflater.inflate(R.layout.input_frag, null);

        contentView.setDrawingCacheEnabled(false);

        mSubmit = (Button)contentView.findViewById(R.id.btnSubmit);

        mName = (EditText)contentView.findViewById(R.id.editName);

        mOccupation = (EditText)contentView.findViewById(R.id.editOccupation);

        mDesignation = (EditText)contentView.findViewById(R.id.editDesignation);

        Bundle bundle = getArguments();

        if ( bundle != null ) {

            mName.setText(bundle.getString("name"));

            mOccupation.setText(bundle.getString("occupation"));

            mDesignation.setText(bundle.getString("designation"));

        }

        return contentView;

    }

    @Override

    public void onStart() {

         super.onStart();

        mSubmit.setOnClickListener(submitClickListener);

    }

    //Define Interface for callback to activity.

    public interface ActivityListener {

        public void getData (Bundle bundle);

    }

}

input_frag.xml

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

<LinearLayout

    xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:orientation="vertical"

    android:padding="20dp" >

    <TextView

        android:id="@+id/name"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Name"

        android:textSize="20dp" />

    <EditText

        android:id="@+id/editName"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:hint="Enter your name"

        android:textSize="20dp"

        android:padding="10dp"

        android:layout_marginTop="20dp" />

    <TextView

        android:id="@+id/occupation"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Occupation"

        android:textSize="20dp"

        android:layout_marginTop="20dp" />

    <EditText

        android:id="@+id/editOccupation"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:hint="Enter your Occupation"

        android:textSize="20dp"

        android:padding="10dp"

        android:layout_marginTop="20dp" />

    <TextView

        android:id="@+id/designation"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Designation"

        android:textSize="20dp"

        android:layout_marginTop="20dp" />

    <EditText

        android:id="@+id/editDesignation"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:hint="Enter your Designation"

        android:textSize="20dp"

        android:padding="10dp"

        android:layout_marginTop="20dp" />

    <Button

        android:id="@+id/btnSubmit"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:text="Submit"

        android:textSize="20dp"

        android:layout_marginTop="20dp" />

</LinearLayout>

5.  Create DetailFragment.

DetailFragment.java

public class DetailFragment extends Fragment{

    private TextView mInfo;

    private Button mEditDetail, mClose;

    private Bundle mBundleData;

    private OnClickListener editClickListener = new OnClickListener() {

        public void onClick(View v) {

            InputFragment inputFragment = new InputFragment();

            inputFragment.setArguments(mBundleData);

            getFragmentManager().beginTransaction().

            replace(R.id.frameLayout, inputFragment).addToBackStack(null).commit();

        }

    };

    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container,

            Bundle savedInstanceState) {

        View contentView = inflater.inflate(R.layout.detail_frag, null);

        contentView.setDrawingCacheEnabled(false);

        mInfo = (TextView)contentView.findViewById(R.id.detail);

        mEditDetail = (Button)contentView.findViewById(R.id.btnEdit);

        mBundleData = getArguments();

        if ( mBundleData != null ) {

            mInfo.setText("Name:  " + mBundleData.getString("name") + "\n"

                    + "Occupation:  " + mBundleData.getString("occupation") + "\n"

                    + "Designation:  " + mBundleData.getString("designation") + "\n" );

        }

        return contentView;

    }

    @Override

    public void onStart() {

        super.onStart();

        mEditDetail.setOnClickListener(editClickListener);

    }

}

detail_frag.xml

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

<LinearLayout

    xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:orientation="vertical"

    android:gravity="center" >

    <TextView

        android:id="@+id/detail"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:textSize="20dp" />

    <Button

        android:id="@+id/btnEdit"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:text="Edit User Details"

        android:textSize="20dp" />

</LinearLayout>

Source:

http://developer.android.com/guide/topics/fundamentals/fragments.html

http://www.vogella.de/articles/Android/article.html#fragments

http://stackoverflow.com/

Download and Install App programmatically

Science Fantasy

You can download an apk file of any application and install it thru your app and all this you can do programmatically. Let's see how to do it:

1. First download the apk file programmatically and store it in external storage.

private void download(){
try {
    URL url = new URL("url from apk file is to be downloaded");
    HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
    urlConnection.setRequestMethod("GET");
    urlConnection.setDoOutput(true);
    urlConnection.connect();

    File sdcard = Environment.getExternalStorageDirectory();
    File file = new File(sdcard, "filename.ext");

    FileOutputStream fileOutput = new FileOutputStream(file);
    InputStream inputStream = urlConnection.getInputStream();

    byte[] buffer = new byte[1024];
    int bufferLength = 0;

    while ( (bufferLength = inputStream.read(buffer)) > 0 ) {
        fileOutput.write(buffer, 0, bufferLength);
    }
    fileOutput.close();

} catch (MalformedURLException e) {
        e.printStackTrace();
} catch (IOException e) {
        e.printStackTrace();
}
}

Permission: To write to external storage, you need to add this permission:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Note: The above download method can be used to download any file and store the file to external storage.

2. Now initiate installing process.

private void initiateInstallation(){
    Intent intent = new Intent(Intent.ACTION_VIEW);
    Uri uri = Uri.fromFile(new File("/sdcard/filename.apk"));
    intent.setDataAndType(uri, "application/vnd.android.package-archive");
    startActivity(intent);
}

Working with Call log

We often need to access call log details i.e. incoming number, outgoing number, missed call. We want to modify the call log i.e. make your own entry, deleting an existing entry. So let's see how can we do all this:

Uri UriCalls = Uri.parse("content://call_log/calls");

Cursor cursor = getApplicationContext().getContentResolver().query(UriCalls, null, null, null, null);

//Reading call log entries...

if(cursor.getCount() > 0){

    cursor.moveToFirst();

    while(!cursor.isAfterLast()){

        String number = cursor.getString(cursor.getColumnIndex(CallLog.Calls.NUMBER)); // for  number

        String name = cursor.getString(cursor.getColumnIndex(CallLog.Calls.CACHED_NAME));// for name

        String duration = cursor.getString(cursor.getColumnIndex(CallLog.Calls.DURATION));// for duration

        int type = Integer.parseInt(cursor.getString(cursor.getColumnIndex(CallLog.Calls.TYPE)));// for call type, Incoming or out going

        cursor.moveToNext();

    }

}

//Inserting values in call log...

ContentValues values = new ContentValues();

values.put(CallLog.Calls.NUMBER, number);

values.put(CallLog.Calls.CACHED_NAME, name);

values.put(CallLog.Calls.CACHED_NUMBER_LABEL, label);

values.put(CallLog.Calls.DATE, date);

values.put(CallLog.Calls.DURATION, duration);

values.put(CallLog.Calls.TYPE, myCallType);

getApplicationContext().getContentResolver().insert(CallLog.Calls.CONTENT_URI, values);

//Deleting entry in call log...

String queryString= "NUMBER='" + number + "'";

if (cursor.getCount() > 0){

        getApplicationContext().getContentResolver().delete(UriCalls, queryString, null);

}

Permission:

<uses-permission android:name="android.permission.WRITE_CONTACTS" />

<uses-permission android:name="android.permission.READ_CONTACTS" />

Note: Please refer this doc over call log for more clearity.

Block Home Key

I searched a lot to block Home key but no success and finally I got it and here it is for you guys.

@Override
public void onAttachedToWindow() {

this.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD);
super.onAttachedToWindow();

}

Note: You should never block the Home key. Please see this post before doing so.

Auto App start on Boot Completion

You can start your application when the device starts again thru BroadcastReceiver:

public class PhoneStateReceiver extends BroadcastReceiver{

   

    @Override

    public void onReceive(final Context context, Intent intent) {

       

        if(intent.getAction().equals(Intent.ACTION_BOOT_COMPLETED)){

            Intent launch = new Intent(context, ActivityToLaunch.class);

            launch.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

            context.startActivity(launch);

        }

    }

}

In your manifest add this:

<receiver android:name=".receiver.PhoneStateReceiver">

    <intent-filter>

        <action android:name="android.intent.action.BOOT_COMPLETED" />

    </intent-filter>

</receiver>   

Add permission:

<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />

Rating your code from A to F

Assuming that a piece of code is functional and that it complies with its requirements, that piece of code can be rated from A to F based in two parameters, the simplicity and the extensibility.

Simplicity

The simplicity is a characteristic that tells us how easy is to understand and read the code. In order to determine how simple a code is, the following can be taken into consideration.

• Good identifiers for Class names, variables, methods…
• Straight forward logic.
• Crisp and minimal abstractions.
• Low representational gap. The representational gap is how different is the domain logic of an application from its design, having a low representational gap means that the design has very few differences with the domain logic it represents.

The simplicity is classified in “Very simple”, “Simple” or “Not simple”
Very simple: Code that doesn’t require additional documentation to be understood, any developer can pick up the code and do changes without further explanation.
Simple: Code that requires some additional documentation to be understood, only developers with some background on the design and in the business domain knowledge will be able to do changes.
Not simple: Code that requires lots of additional documentation to be understood, only senior developers with a deep knowledge of the application will be able to do changes.

 

Extensibility

The extensibility is a characteristic that tells us how easy will be to add new functionality on top of the current code, don’t confuse extensibility with over engineering, which is a bad practice. In order to determine how extensible a code is, the following can be taken into consideration.

• Atomicity, use of DRY.
• Testability. Code that includes unit tests.
• Use of design patterns.
• Low coupling

The extensibility is classified in “Very extensible”, “Extensible” or “Not extensible”
Very extensible: To add new functionality on the top of the code is really easy, no refactoring would be necessary.
Extensible: To add new functionality on the top of the existing code is relatively easy, minor refactoring would be necessary.
Not extensible: To add new functionality on the top of the existing code is difficult, complex refactoring, even redesign would be necessary.

Code Rates

 

A- Excellent code.

A is the best rate for code, it can’t be more simple and it can’t be more extensible, the problem with A codes is that is almost impossible to achieve, usually there is a trade off between extensibility and readability, that’s why I always recommend to produce B codes.

 

B- Good code

B code is good code, B code will ensure that the maintenance of the application will be much easier. This code is the one I recommend to aim for.

 

C- Average code

C code is what some developers consider good enough, if we are under a tight deadline or high pressure we might have to aim for this rate of code. Maintenance of the application is harder than with B code but still is possible.

 

D- Dangerous code

With D code still is possible to maintain the application, but it takes a lot of time to perform any change and the risk to enter new bugs doing so is high, some teams don’t want to refactor D codes because they don’t want to change something that is working, that’s an error, D codes easily become E codes after a few changes and then it will become unmaintainable.

 

E- Bad code

E code is bad code, the application is unmaintainable, urgent changes are necessary, still there is time for reaction to change the code and improve it.

 

F- Start over again

Not only the application is unmaintainable, the code should be scrapped and created again from scratch

Android Intents

//show webapp:

Uri uri = Uri.parse("http://www.google.com");

Intent intent  = new Intent(Intent.ACTION_VIEW,uri);

startActivity(intent);

//show maps:

Uri uri = Uri.parse("geo:38.899533,-77.036476");

Intent intent = new Intent(Intent.Action_VIEW,uri);

startActivity(intent);

//show ways

Uri uri = Uri.parse("http://maps.google.com/maps?f=d&saddr=startLat%20startLng&daddr=endLat%20endLng&hl=en");

Intent intent = new Intent(Intent.ACTION_VIEW,URI);

startActivity(intent);

//call dial program

Uri uri = Uri.parse("tel:xxxxxx");

Intent intent = new Intent(Intent.ACTION_DIAL, uri); 

startActivity(intent); 

Uri uri = Uri.parse("tel.xxxxxx");

Intent intent =new Intent(Intent.ACTION_CALL,uri);

startActivity(intent);

//don't forget add this config:<uses-permission id="android.permission.CALL_PHONE" />

//send sms/mms

//call sender program

Intent intent = new Intent(Intent.ACTION_VIEW);  

intent.putExtra("sms_body", "The SMS text");  

intent.setType("vnd.android-dir/mms-sms");  

startActivity(intent); 

//send sms

Uri uri = Uri.parse("smsto:0800000123");  

Intent intent = new Intent(Intent.ACTION_SENDTO, uri);  

intent.putExtra("sms_body", "The SMS text");  

startActivity(intent); 

//send mms

Uri uri = Uri.parse("content://media/external/images/media/23");  

Intent intent = new Intent(Intent.ACTION_SEND);  

intent.putExtra("sms_body", "some text");  

intent.putExtra(Intent.EXTRA_STREAM, uri);  

intent.setType("image/png");  

startActivity(intent);

//send email

Uri uri = Uri.parse("mailto:xxx@abc.com");

Intent intent = new Intent(Intent.ACTION_SENDTO, uri);

startActivity(intent);

Intent intent = new Intent(Intent.ACTION_SEND);  

intent.putExtra(Intent.EXTRA_EMAIL, "me@abc.com");  

intent.putExtra(Intent.EXTRA_TEXT, "The email body text");  

intent.setType("text/plain");  

startActivity(Intent.createChooser(intent, "Choose Email Client")); 

Intent intent=new Intent(Intent.ACTION_SEND);    

String[] tos={"me@abc.com"};    

String[] ccs={"you@abc.com"};    

intent.putExtra(Intent.EXTRA_EMAIL, tos);    

intent.putExtra(Intent.EXTRA_CC, ccs);    

intent.putExtra(Intent.EXTRA_TEXT, "The email body text");    

intent.putExtra(Intent.EXTRA_SUBJECT, "The email subject text");    

intent.setType("message/rfc822");    

startActivity(Intent.createChooser(intent, "Choose Email Client"));  

//add extra

Intent intent = new Intent(Intent.ACTION_SEND);  

intent.putExtra(Intent.EXTRA_SUBJECT, "The email subject text");  

intent.putExtra(Intent.EXTRA_STREAM, "file:///sdcard/mysong.mp3");  

sendIntent.setType("audio/mp3");  

startActivity(Intent.createChooser(intent, "Choose Email Client"));

//play media

Intent intent = new Intent(Intent.ACTION_VIEW);

Uri uri = Uri.parse("file:///sdcard/song.mp3");

intent.setDataAndType(uri, "audio/mp3");

startActivity(intent);

Uri uri = Uri.withAppendedPath(MediaStore.Audio.Media.INTERNAL_CONTENT_URI, "1");  

Intent intent = new Intent(Intent.ACTION_VIEW, uri);  

startActivity(intent); 

//Uninstall

Uri uri = Uri.fromParts("package", strPackageName, null);  

Intent intent = new Intent(Intent.ACTION_DELETE, uri);  

startActivity(intent);

//uninstall apk

Uri uninstallUri = Uri.fromParts("package", "xxx", null);

Intent intent = new Intent(Intent.ACTION_DELETE, uninstallUri);

startActivity(intent);

//install apk

Uri installUri = Uri.fromParts("package", "xxx", null);

Intent intent = new Intent(Intent.ACTION_PACKAGE_ADDED, installUri);

startActivity(intent);

//play audio

Uri playUri = Uri.parse("file:///sdcard/download/everything.mp3");

Intent intent = new Intent(Intent.ACTION_VIEW, playUri);

startActivity(intent);

//send extra

Intent intent = new Intent(Intent.ACTION_SEND); 

intent.putExtra(Intent.EXTRA_SUBJECT, "The email subject text"); 

intent.putExtra(Intent.EXTRA_STREAM, "file:///sdcard/eoe.mp3"); 

sendIntent.setType("audio/mp3"); 

startActivity(Intent.createChooser(intent, "Choose Email Client"));

//search

Uri uri = Uri.parse("market://search?q=pname:pkg_name"); 

Intent intent = new Intent(Intent.ACTION_VIEW, uri); 

startActivity(intent); 

//where pkg_name is the full package path for an application 

//show program detail page

Uri uri = Uri.parse("market://details?id=app_id"); 

Intent intent = new Intent(Intent.ACTION_VIEW, uri); 

startActivity(intent); 

//where app_id is the application ID, find the ID 

//by clicking on your application on Market home 

//page, and notice the ID from the address bar

//search google

Intent intent = new Intent();

intent.setAction(Intent.ACTION_WEB_SEARCH);

intent.putExtra(SearchManager.QUERY,"searchString")

startActivity(intent);

SQLite

1. SQLite in Android

SQLite is an Open Source Database which is embedded into Android. SQLight supports standard relational database features like SQL syntax, transactions and prepared statements. In addition it requires only little memory at runtime (approx. 250 KByte).

Using SQLite in Android does not require any database setup or administration. You specify the SQL for working with the database and the database is automatically managed for you.

Working with databases in Android can be slow due to the necessary I/O. Therefore is it recommended to perform this task in an AsyncTask . Please see Android Background Processing Tutorial for details.

SQLite supports the data types TEXT (similar to String in Java), INTEGER (similar to long in Java) and REAL (similar to double in Java). All other types must be converted into on of these fields before saving them in the database. SQLight itself does not validate if the types written to the columns are actually of the defined type, you can write an integer into a string column.

If your application creates an database this database is saved in the directory "DATA/data/APP_NAME/databases/FILENAME". "DATA" is the path which Environment.getDataDirectory() returns, "APP_NAME" is your application name and "FILENAME" is the name you give the database during creation. Environment.getDataDirectory() usually return the SD card as location.

A SQlite database is private to the application which creates it. If you want to share data with other applications you can use a Content Provider.

2. SQLiteOpenHelper

To create and upgrade a database in your Android application you usually subclass "SQLiteOpenHelper". In this class you need to override the methods onCreate() to create the database and onUpgrade() to upgrade the database in case of changes in the database schema. Both methods receive an "SQLiteDatabase" object.

SQLiteOpenHelper provides the methods getReadableDatabase() and getWriteableDatabase() to get access to an "SQLiteDatabase" object which allows database access either in read or write mode.

For the primary key of the database you should always use the identifier "_id" as some of Android functions rely on this standard.

3. SQLiteDatabase and Cursor

"SQLiteDatabase" provides the methods insert(), update() and delete() and execSQL() method which allows to execute directly SQL. The object "ContentValues" allow to define key/values for insert and update. The key is the column and the value is the value for this column.

Queries can be created via the method rawQuery() which accepts SQL or query() which provides an interface for specifying dynamic data or SQLiteQueryBuilder. SQLiteBuilder is similar to the interface of an content provider therefore it is typically used in ContentProviders. A query returns always a "Cursor".

The method query has the parameters String dbName, int[] columnNames, String whereClause, String[] valuesForWhereClause, String[] groupBy, String[] having, String[] orderBy. If all data should be selected you can pass "null" as the where clause. The where clause is specified without "where", for example "_id=19 and summary=?". If several values are required via ? you pass them in the valuesForWhereClause array to the query. In general if something is not required you can pass "null", e.g. for the group by clause.

A Cursor represents the result of a query. To get the number of elements use the method getCount(). To move between individual data rows, you can use the methods moveToFirst() and moveToNext(). Via the method isAfterLast() you can check if there is still some data.

Launching other app from my app

Launch other application of the device from your application:

Intent intent = getPackageManager().getLaunchIntentForPackage(packageName);

      intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

      intent.addFlags(Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED);

      if (null != intent) {

      try {

             startActivity(intent);

      } catch(Exception e) {  }

    }

Note: You need to know the package name to use the above code. For package name:

http://lovingandroid.blogspot.com/2011/08/getting-package-name-of-installed-app.html

Getting Package Name of Installed app

Note: A lot of people need to fetch the package name, application name of the installed application on the device.Here is the code:

ArrayList<PackageInfo> res = new ArrayList<PackageInfo>();

PackageManager pm = ctx.getPackageManager();

List<PackageInfo> packs = pm.getInstalledPackages(0);

for(int i=0;i<packs.size();i++) {

    PackageInfo p = packs.get(i);

    String description = (String) p.applicationInfo.loadDescription(pm);

    String  label= p.applicationInfo.loadLabel(pm).toString();

    String packageName = p.packageName;

    String versionName = p.versionName;

    String versionCode = p.versionCode;

    String icon = p.applicationInfo.loadIcon(pm);

//Continue to extract other info about the app...

}

Note: Add this permission to the manifest file:

<uses-permission android:name="android.permission.GET_TASKS" />