Custom Content Provider Example
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1. Create: StudentsProvider.java
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import java.util.HashMap;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;

import android.database.Cursor;
import android.database.SQLException;

import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;

import android.net.Uri;
import android.text.TextUtils;

public class StudentsProvider extends ContentProvider {
    static final String PROVIDER_NAME = "com.example.MyApplication.StudentsProvider";
    static final String URL = "content://" + PROVIDER_NAME + "/students";
    static final Uri CONTENT_URI = Uri.parse(URL);

    static final String _ID = "_id";
    static final String NAME = "name";
    static final String GRADE = "grade";

    private static HashMap<String, String> STUDENTS_PROJECTION_MAP;

    static final int STUDENTS = 1;
    static final int STUDENT_ID = 2;

    static final UriMatcher uriMatcher;
    static{
        uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        uriMatcher.addURI(PROVIDER_NAME, "students", STUDENTS);
        uriMatcher.addURI(PROVIDER_NAME, "students/#", STUDENT_ID);
    }

    /**
     * Database specific constant declarations
     */

    private SQLiteDatabase db;
    static final String DATABASE_NAME = "College";
    static final String STUDENTS_TABLE_NAME = "students";
    static final int DATABASE_VERSION = 1;
    static final String CREATE_DB_TABLE =
            " CREATE TABLE " + STUDENTS_TABLE_NAME +
                    " (_id INTEGER PRIMARY KEY AUTOINCREMENT, " +
                    " name TEXT NOT NULL, " +
                    " grade TEXT NOT NULL);";

    /**
     * Helper class that actually creates and manages
     * the provider's underlying data repository.
     */

    private static class DatabaseHelper extends SQLiteOpenHelper {
        DatabaseHelper(Context context){
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(CREATE_DB_TABLE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            db.execSQL("DROP TABLE IF EXISTS " +  STUDENTS_TABLE_NAME);
            onCreate(db);
        }
    }

    @Override
    public boolean onCreate() {
        Context context = getContext();
        DatabaseHelper dbHelper = new DatabaseHelper(context);

        /**
         * Create a write able database which will trigger its
         * creation if it doesn't already exist.
         */

        db = dbHelper.getWritableDatabase();
        return (db == null)? false:true;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        /**
         * Add a new student record
         */
        long rowID = db.insert(	STUDENTS_TABLE_NAME, "", values);

        /**
         * If record is added successfully
         */
        if (rowID > 0) {
            Uri _uri = ContentUris.withAppendedId(CONTENT_URI, rowID);
            getContext().getContentResolver().notifyChange(_uri, null);
            return _uri;
        }

        throw new SQLException("Failed to add a record into " + uri);
    }

    @Override
    public Cursor query(Uri uri, String[] projection,
                        String selection,String[] selectionArgs, String sortOrder) {
        SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
        qb.setTables(STUDENTS_TABLE_NAME);

        switch (uriMatcher.match(uri)) {
            case STUDENTS:
                qb.setProjectionMap(STUDENTS_PROJECTION_MAP);
                break;

            case STUDENT_ID:
                qb.appendWhere( _ID + "=" + uri.getPathSegments().get(1));
                break;

            default:
        }

        if (sortOrder == null || sortOrder == ""){
            /**
             * By default sort on student names
             */
            sortOrder = NAME;
        }

        Cursor c = qb.query(db,	projection,	selection,
                selectionArgs,null, null, sortOrder);
        /**
         * register to watch a content URI for changes
         */
        c.setNotificationUri(getContext().getContentResolver(), uri);
        return c;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        int count = 0;
        switch (uriMatcher.match(uri)){
            case STUDENTS:
                count = db.delete(STUDENTS_TABLE_NAME, selection, selectionArgs);
                break;

            case STUDENT_ID:
                String id = uri.getPathSegments().get(1);
                count = db.delete( STUDENTS_TABLE_NAME, _ID +  " = " + id +
                                (!TextUtils.isEmpty(selection) ? " AND (" + selection + ')' : ""), selectionArgs);
                break;
            default:
                throw new IllegalArgumentException("Unknown URI " + uri);
        }

        getContext().getContentResolver().notifyChange(uri, null);
        return count;
    }

    @Override
    public int update(Uri uri, ContentValues values,
                      String selection, String[] selectionArgs) {
        int count = 0;
        switch (uriMatcher.match(uri)) {
            case STUDENTS:
                count = db.update(STUDENTS_TABLE_NAME, values, selection, selectionArgs);
                break;

            case STUDENT_ID:
                count = db.update(STUDENTS_TABLE_NAME, values,
                        _ID + " = " + uri.getPathSegments().get(1) +
                                (!TextUtils.isEmpty(selection) ? " AND (" +selection + ')' : ""), selectionArgs);
                break;
            default:
                throw new IllegalArgumentException("Unknown URI " + uri );
        }

        getContext().getContentResolver().notifyChange(uri, null);
        return count;
    }

    @Override
    public String getType(Uri uri) {
        switch (uriMatcher.match(uri)){
            /**
             * Get all student records
             */
            case STUDENTS:
                return "vnd.android.cursor.dir/vnd.example.students";
            /**
             * Get a particular student
             */
            case STUDENT_ID:
                return "vnd.android.cursor.item/vnd.example.students";
            default:
                throw new IllegalArgumentException("Unsupported URI: " + uri);
        }
    }
}


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2. Change: MainActivity.java
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import android.net.Uri;
import android.os.Bundle;
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {

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

    public void onClickAddName(View view) {
        // Add a new student record
        ContentValues values = new ContentValues();
        values.put(StudentsProvider.NAME,
                ((EditText) findViewById(R.id.name)).getText().toString());

        values.put(StudentsProvider.GRADE,
                ((EditText) findViewById(R.id.grade)).getText().toString());

        Uri uri = getContentResolver().insert(StudentsProvider.CONTENT_URI, values);
        Toast.makeText(getBaseContext(), uri.toString(), Toast.LENGTH_LONG).show();
    }

    public void onClickRetrieveStudents(View view) {
        // Retrieve student records
        String URL = "content://com.example.MyApplication.StudentsProvider";

        Uri students = Uri.parse(URL);
        Cursor c = getContentResolver().query(students, null, null, null, null);
        
        String myStudents=null;

        for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
            myStudents = myStudents + c.getString(c.getColumnIndex(StudentsProvider._ID)) + ", " + c.getString(c.getColumnIndex(StudentsProvider.NAME)) + ", " + c.getString(c.getColumnIndex(StudentsProvider.GRADE));
        }
        Toast.makeText(this, myStudents, Toast.LENGTH_SHORT).show();   
    }
}

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3. Change: activity_main.xml
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<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/name"
        android:hint="Name"
        android:textColorHint="@android:color/holo_blue_bright" />

    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/grade"
        android:hint="Grade"
        android:textColorHint="@android:color/holo_blue_bright" />

    <Button
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/button2"
        android:text="Add Name"
        android:onClick="onClickAddName"/>

    <Button
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Retrieve student"
        android:id="@+id/button"
        android:onClick="onClickRetrieveStudents"/>

</LinearLayout>

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4. Add to the manifest inside of <Application>
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<provider android:name="StudentsProvider" android:authorities="com.example.MyApplication.StudentsProvider"/>