Home > Uncategorized > Android, ListView and Databases

Android, ListView and Databases

Here I’ll show how to get data from the Sqlite database and show them into ListView. 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:
What you will learn –

ListView
ListView icon
ListAdapter
ListActivity
ListActivity and Layout
What is Adapter
ListViews and performance
Create ListActivity Show Data from Array without Database
ListActivity with own layout
Implementing your own ListAdapter
Implementing your own adapter
Rows interacting with the data model – CheckBox
Use of SimpleCursorAdapter – Database
What is SQLite
SQLite in Android – brief
rawQuery() Example
query() Example
What is Cursor?
ListViews, ListActivities and SimpleCursorAdapter –Details
ListView with Database


ListView

The display of Lists is a very common pattern in mobile applications. The user gets a list of items can scroll through them and select one item. This selection is used to trigger something else.
Android provides the view ListView which is capable of displaying a scrollable list of items.
A view that shows items in a vertically scrolling list. The items come from the ListAdapter associated with this view.
You can directly use the ListView in your layout as any other user interface component.

ListView Icon –
List view icons look a lot like dialog icons, but they use an inner shadow effect where the light source is above the object.

ListAdapter
Extended Adapter that is the bridge between a ListView and the data that backs the list. Frequently that data comes from a Cursor, but that is not required. The ListView can display any data provided that it is wrapped in a ListAdapter.

ListActivity
In case your Activity is primary showing a list you can extend the activity ListActivity which simplifies the handling of a ListView.

  • ListActivity extends Activity and provides simplified handling of lists.
  • ListActivity contains a ListAdapter which is responsible for managing the data.
  • This adapter must be set in the onCreate() method of your Activity via the setListAdapter() method.
  • If the user select in the list a list entry the onListItemClick() method will be called. This method allows to access the selected element.
  • Android provides already some default layouts which you can use in your Adapter, e.g.
  • android.R.layout.simple_list_item1.

    ListActivity and Layout

  • An ListActivity has per default a layout available which includes a default ListView.
  • Therefore you are not required to use the setContentView() to assign a layout to your Activity method.
  • The default layout only contains a ListView
  • In case you need more Views in your layout, you can use you own layout for ListActivity.
  • In this case your layout must have an ListView element with the android:id attribute set to @android:id/list.
  • What is Adapter ?

  • ListView gets the data to display via an adapter.
  • An adapter which must extend BaseAdapter and is responsible for providing the data model for the list and for converting the data into the fields of the list.
  • Android has two standard adapters, ArrayAdapter and CursorAdapter.
  • ArrayAdapter can handle data based on Arrays or Lists while CursorAdapter handle database related data.
  • You can develop your own Adapter by extending these classes or the BaseAdapter class.
  • The most important method of the Adapter is getView().
  • The getView() method is called for every line in the ListView to determine which data should be displayed in the line and how.
  • In an ListView not all rows are visible at the same time.
  • If the user scrolls the list then certain rows (and their associated views) will not be visible anymore.
  • Via the parameter convertView in the getView() method you can re-use an existing row and fill the Views of this row with new data.
  • If this convertView is not null it can be re-used, e.g. you can only update the content of the row and you don’t have to load the layout for the view which is a big performance saver as handling of XML files is an expensive operation.
  • ListViews and performance
    Mobile Memory and processor is very less compare to desktop, so performance keep in mind to develop an application.

  • Displaying a large dataset must be efficiently implemented on a mobile device.
  • herefore the ListView only creates views (widget) if needed and attach them to the view hierarchy.
  • The default Adapter implementation for a ListView will recycle views,
  • if a row is not displayed anymore it will be recycled and only its content will change.
  • If you implement your own adapter for a view you also should do this to avoid performance problems
  • Create ListActivity Show Data from Array without Database

  • We use the default ArrayAdapter class as Adapter for our ListView and a predefined layout from Android.
  • Create a new Android project com.sst.example.listactivity with the Activity called MyListActivity.
  • Change MyListActivity to the following. Note that the setContentView() method is not used.

  • package com.sst.example.listactivity;

    import android.app.ListActivity;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.ArrayAdapter;
    import android.widget.ListView;
    import android.widget.Toast;

    public class MyListActivity extends ListActivity {
    public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
    "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
    "Linux", "OS/2" };
    ArrayAdapter adapter = new ArrayAdapter(this,
    android.R.layout.simple_list_item_1, values);
    setListAdapter(adapter);
    }

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
    String item = (String) getListAdapter().getItem(position);
    Toast.makeText(this, item + " selected", Toast.LENGTH_LONG).show();
    }
    }

    ListActivity with own layout

  • u can also define your own layout for the rows and assign this layout to your adapter.
  • If you do this the layout will be the same for every entry,
  • Create the following layout file “rowlayout.xml” in the res/layout folder of your project “com.sst.example.listactivity”.

  • <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" >

    <ImageView
    android:id="@+id/icon"
    android:layout_width="22px"
    android:layout_height="22px"
    android:layout_marginLeft="4px"
    android:layout_marginRight="10px"
    android:layout_marginTop="4px"
    android:src="@drawable/ic_launcher" >
    </ImageView>

    <TextView
    android:id="@+id/label"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@+id/label"
    android:textSize="20px" >
    </TextView>

    </LinearLayout>

  • Change activity to the following.
  • This is almost the same coding as in the previous example
  • the only difference is that we are using our own layout in the ArrayAdapter and telling the adapter which UI element should contains the text.
  • This was not necessary in the previous example a standard layout was used

  • package com.sst.example.listactivity;

    import android.app.ListActivity;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.ArrayAdapter;
    import android.widget.ListView;
    import android.widget.Toast;

    public class MyListActivity extends ListActivity {
    public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
    "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
    "Linux", "OS/2" };
    // Use your own layout
    ArrayAdapter adapter = new ArrayAdapter(this,
    R.layout.rowlayout, R.id.label, values);
    setListAdapter(adapter);
    }

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
    String item = (String) getListAdapter().getItem(position);
    Toast.makeText(this, item + " selected", Toast.LENGTH_LONG).show();
    }
    }

    Implementing your own ListAdapter

  • If you want to use different layouts based on in row data you must implement your own adapter for the ListView. You would implement BaseAdapter or could extend an existing adapter like ArrayAdapter.
  • Here we will implementation at least override the getView() method.
  • This method is responsible for creating the individual rows of your ListView. The getView() method returns a View for each row.
  • This View is typically a Layout ( ViewGroup ) and contains several other Views, e.g. an ImageView and a TextView.
  • Within the getView() method you would typically inflate an XML based layout and then set the values of the individual Views in the layout based on the data for the row.
  • The individual elements in the layout can be found via the findViewById() method call.
  • To optimize performance you would buffer data and reuse existing rows if possible.
  • To read an layout from an XML resource in the getView() method you can use the system service LayoutInflator.
  • This service can get accessed via the Activity or via the context .getSystemService(Context.LAYOUT_INFLATER_SERVICE); method call.
  • Implementing your own adapter

  • we extend ArrayAdapter but we could also directly implement BaseAdapter

  • public class MySimpleArrayAdapter extends ArrayAdapter {
    private final Context context;
    private final String[] values;

    public MySimpleArrayAdapter(Context context, String[] values) {
    super(context, R.layout.rowlayout, values);
    this.context = context;
    this.values = values;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
    LayoutInflater inflater = (LayoutInflater) context
    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View rowView = inflater.inflate(R.layout.rowlayout, parent, false);
    TextView textView = (TextView) rowView.findViewById(R.id.label);
    ImageView imageView = (ImageView) rowView.findViewById(R.id.icon);
    textView.setText(values[position]);
    // Change the icon for Windows and iPhone
    String s = values[position];
    if (s.startsWith("Windows7") || s.startsWith("iPhone")
    || s.startsWith("Solaris")) {
    imageView.setImageResource(R.drawable.no);
    } else {
    imageView.setImageResource(R.drawable.ok);
    }

    return rowView;
    }
    }

  • place two image ie. “no.png” and “ok.png”. in the “res/drawable-mdpi” folder.
  • To use this adapter, change the class “MyList” to the following.

  • public class MyListActivity extends ListActivity {
    public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
    "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
    "Linux", "OS/2" };
    MySimpleArrayAdapter adapter = new MySimpleArrayAdapter(this, values);
    setListAdapter(adapter);
    }

    }


    Adding a longclick listener to the list items
    import android.app.ListActivity;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.AdapterView;
    import android.widget.AdapterView.OnItemLongClickListener;
    import android.widget.ArrayAdapter;
    import android.widget.ListView;
    import android.widget.Toast;

    public class MyList extends ListActivity {

    /** Called when the activity is first created. */

    public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    // Create an array of Strings, that will be put to our ListActivity
    String[] names = new String[] { "Linux", "Windows7", "Eclipse", "Suse",
    "Ubuntu", "Solaris", "Android", "iPhone" };
    ArrayAdapter adapter = new MyPerformanceArrayAdapter(this, names);
    setListAdapter(adapter);
    ListView list = getListView();
    list.setOnItemLongClickListener(new OnItemLongClickListener() {

    @Override
    public boolean onItemLongClick(AdapterView parent, View view,
    int position, long id) {
    Toast.makeText(MyList.this,
    "Item in position " + position + " clicked",
    Toast.LENGTH_LONG).show();
    // Return true to consume the click event. In this case the
    // onListItemClick listener is not called anymore.
    return true;
    }
    });
    }

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
    super.onListItemClick(l, v, position, id);
    // Get the item that was clicked
    Object o = this.getListAdapter().getItem(position);
    String keyword = o.toString();
    Toast.makeText(this, "You selected: " + keyword, Toast.LENGTH_SHORT)
    .show();

    }

    }

    Rows interacting with the data model - CheckBox
    Your row layout can also contain views which interact with the underlying data model.
    For example you can have a "Checkbox" view in your row and if the checkbox is selected you change the data which is displayed in the row.

  • Create a new row layout "rowbuttonlayout.xml"

  • <?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >

    <TextView
    android:id="@+id/label"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@+id/label"
    android:textSize="30px" >
    </TextView>

    <CheckBox
    android:id="@+id/check"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentRight="true"
    android:layout_marginLeft="4px"
    android:layout_marginRight="10px" >
    </CheckBox>

    </RelativeLayout >

  • create for this example the class "Model" which hold the name and the information if this element is currently selected.

  • public class Model {

    private String name;
    private boolean selected;

    public Model(String name) {
    this.name = name;
    selected = false;
    }

    public String getName() {
    return name;
    }

    public void setName(String name) {
    this.name = name;
    }

    public boolean isSelected() {
    return selected;
    }

    public void setSelected(boolean selected) {
    this.selected = selected;
    }

    }

  • Create the following Adapter.
  • This adapter will add a listener on the Checkbox.
  • If the checkbox is selected the underlying data of the model is also changed.
  • Search Checkbox gets its model element assigned via the setTag() method.

  • import android.app.Activity;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ArrayAdapter;
    import android.widget.CheckBox;
    import android.widget.CompoundButton;
    import android.widget.TextView;

    public class InteractiveArrayAdapter extends ArrayAdapter {

    private final List list;
    private final Activity context;

    public InteractiveArrayAdapter(Activity context, List list) {
    super(context, R.layout.rowbuttonlayout, list);
    this.context = context;
    this.list = list;
    }

    static class ViewHolder {
    protected TextView text;
    protected CheckBox checkbox;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
    View view = null;
    if (convertView == null) {
    LayoutInflater inflator = context.getLayoutInflater();
    view = inflator.inflate(R.layout.rowbuttonlayout, null);
    final ViewHolder viewHolder = new ViewHolder();
    viewHolder.text = (TextView) view.findViewById(R.id.label);
    viewHolder.checkbox = (CheckBox) view.findViewById(R.id.check);
    viewHolder.checkbox
    .setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {

    @Override
    public void onCheckedChanged(CompoundButton buttonView,
    boolean isChecked) {
    Model element = (Model) viewHolder.checkbox
    .getTag();
    element.setSelected(buttonView.isChecked());

    }
    });
    view.setTag(viewHolder);
    viewHolder.checkbox.setTag(list.get(position));
    } else {
    view = convertView;
    ((ViewHolder) view.getTag()).checkbox.setTag(list.get(position));
    }
    ViewHolder holder = (ViewHolder) view.getTag();
    holder.text.setText(list.get(position).getName());
    holder.checkbox.setChecked(list.get(position).isSelected());
    return view;
    }
    }

    SimpleCursorAdapter - Database

  • In case you work with a content provider or directly with the database you can use the SimpleCursorAdapter to define the data for your ListView.
  • Create a new Android project "com.sst.example.listactivity.cursor" with the activity "MyListActivity". Create the following activity.

  • import android.app.ListActivity;
    import android.database.Cursor;
    import android.net.Uri;
    import android.os.Bundle;
    import android.provider.ContactsContract;
    import android.widget.ListAdapter;
    import android.widget.SimpleCursorAdapter;

    public class MyListActivity extends ListActivity {

    /** Called when the activity is first created. */

    @Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Cursor mCursor = getContacts();
    startManagingCursor(mCursor);
    // Now create a new list adapter bound to the cursor.
    // SimpleListAdapter is designed for binding to a Cursor.
    ListAdapter adapter = new SimpleCursorAdapter(this, // Context.
    android.R.layout.two_line_list_item, // Specify the row template
    // to use (here, two
    // columns bound to the
    // two retrieved cursor
    // rows).
    mCursor, // Pass in the cursor to bind to.
    // Array of cursor columns to bind to.
    new String[] { ContactsContract.Contacts._ID,
    ContactsContract.Contacts.DISPLAY_NAME },
    // Parallel array of which template objects to bind to those
    // columns.
    new int[] { android.R.id.text1, android.R.id.text2 });

    // Bind to our new adapter.
    setListAdapter(adapter);
    }

    private Cursor getContacts() {
    // Run query
    Uri uri = ContactsContract.Contacts.CONTENT_URI;
    String[] projection = new String[] { ContactsContract.Contacts._ID,
    ContactsContract.Contacts.DISPLAY_NAME };
    String selection = ContactsContract.Contacts.IN_VISIBLE_GROUP + " = '"
    + ("1") + "'";
    String[] selectionArgs = null;
    String sortOrder = ContactsContract.Contacts.DISPLAY_NAME
    + " COLLATE LOCALIZED ASC";

    return managedQuery(uri, projection, selection, selectionArgs,
    sortOrder);
    }

    }

  • Make sure you give your application the permission to read the contacts. - Manifest file
  • Uses Permissions "android.permission.READ_CONTACTS" in AndroidManifest.xml
  • What is SQLite

  • SQLite is an Open Source Database which is embedded into Android.
  • SQLite supports standard relational database features like SQL syntax, transactions and prepared statements.
  • In addition it requires only little memory at runtime (approx. 250 KByte).
  • 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 one of these fields before saving them in the database.
  • SQLite itself does not validate if the types written to the columns are actually of the defined type, e.g. you can write an integer into a string column and vice versa.
  • SQLite in Android - Brief

  • SQLite is available on every Android device.
  • Using an SQLite database in Android does not require any database setup or administration.
  • You only have to define the SQL statements for creating and updating the database.
  • Afterwards the database is automatically managed for you by the Android platform.
  • Access to an SQLite database involves accessing the filesystem.
  • This can be slow.
  • Therefore it is recommended to perform database operations asynchronously, for example via the AsyncTask class. .
  • If your application creates a database, this database is saved in the directory DATA/data/APP_NAME/databases/DB_NAME.
  • rawQuery() Example

    Cursor cursor = getReadableDatabase().
    rawQuery("select * from todo where _id = ?", new String[] { id });

    query() Example

    return database.query(DATABASE_TABLE,
    new String[] { KEY_ROWID, KEY_CATEGORY, KEY_SUMMARY, KEY_DESCRIPTION },
    null, null, null, null, null);

    What is Cursor?

  • A query returns a Cursor object .
  • A Cursor represents the result of a query and basically points to one row of the query result.
  • This way Android can buffer the query results efficiently;
  • as it does not have to load all data into memory.
  • as it does not have to load all data into memory.

    To get the number of elements of the resulting query use the getCount() method.

  • To move between individual data rows, you can use the moveToFirst() and moveToNext() methods.
  • The isAfterLast() method allows to check if the end of the query result has been reached.
  • Cursor provides typed get*() methods, e.g. getLong(columnIndex), getString(columnIndex) to access the column data for the current position of the result.
  • The "columnIndex" is the number of the column you are accessing.
  • Cursor also provides the getColumnIndexOrThrow(String) method which allows to get the column index for a column name of the table.
  • ListViews, ListActivities and SimpleCursorAdapter -Details

  • ListViews are Views which allow to display a list of elements.
  • ListActivities are specialized Activities which make the usage of ListViews easier.
  • To work with databases and ListViews you can use the SimpleCursorAdapter.
  • The SimpleCursorAdapter allows to set a layout for each row of the ListViews.
  • You also define an array which contains the column names and another array which contains the IDs of Views which should be filled with the data.
  • The SimpleCursorAdapter class will map the columns to the Views based on the Cursor passed to it.
  • To obtain the Cursor you should use the Loader class.
  • ListView with Database

  • Create project with name com.sst.example.sqlite.list with the "TestDatabaseActivity" Activity.

  • import android.content.Context;
    import android.database.sqlite.SQLiteDatabase;
    import android.database.sqlite.SQLiteOpenHelper;
    import android.util.Log;

    public class MySQLiteHelper extends SQLiteOpenHelper {

    public static final String TABLE_COMMENTS = "comments";
    public static final String COLUMN_ID = "_id";
    public static final String COLUMN_COMMENT = "comment";

    private static final String DATABASE_NAME = "commments.db";
    private static final int DATABASE_VERSION = 1;

    // Database creation sql statement
    private static final String DATABASE_CREATE = "create table "
    + TABLE_COMMENTS + "( " + COLUMN_ID
    + " integer primary key autoincrement, " + COLUMN_COMMENT
    + " text not null);";

    public MySQLiteHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase database) {
    database.execSQL(DATABASE_CREATE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    Log.w(MySQLiteHelper.class.getName(),
    "Upgrading database from version " + oldVersion + " to "
    + newVersion + ", which will destroy all old data");
    db.execSQL("DROP TABLE IF EXISTS" + TABLE_COMMENTS);
    onCreate(db);
    }

    }

  • Create the Comment class. This class is our model and contains the data we will save in the database and show in the user interface.

  • public class Comment {
    private long id;
    private String comment;

    public long getId() {
    return id;
    }

    public void setId(long id) {
    this.id = id;
    }

    public String getComment() {
    return comment;
    }

    public void setComment(String comment) {
    this.comment = comment;
    }

    // Will be used by the ArrayAdapter in the ListView
    @Override
    public String toString() {
    return comment;
    }
    }

  • Create the CommentsDataSource class. This class is our DAO. It maintains the database connection and supports adding new comments and fetching all comments.

  • import java.util.ArrayList;
    import java.util.List;

    import android.content.ContentValues;
    import android.content.Context;
    import android.database.Cursor;
    import android.database.SQLException;
    import android.database.sqlite.SQLiteDatabase;

    public class CommentsDataSource {

    // Database fields
    private SQLiteDatabase database;
    private MySQLiteHelper dbHelper;
    private String[] allColumns = { MySQLiteHelper.COLUMN_ID,
    MySQLiteHelper.COLUMN_COMMENT };

    public CommentsDataSource(Context context) {
    dbHelper = new MySQLiteHelper(context);
    }

    public void open() throws SQLException {
    database = dbHelper.getWritableDatabase();
    }

    public void close() {
    dbHelper.close();
    }

    public Comment createComment(String comment) {
    ContentValues values = new ContentValues();
    values.put(MySQLiteHelper.COLUMN_COMMENT, comment);
    long insertId = database.insert(MySQLiteHelper.TABLE_COMMENTS, null,
    values);
    // To show how to query
    Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
    allColumns, MySQLiteHelper.COLUMN_ID + " = " + insertId, null,
    null, null, null);
    cursor.moveToFirst();
    return cursorToComment(cursor);
    }

    public void deleteComment(Comment comment) {
    long id = comment.getId();
    System.out.println("Comment deleted with id: " + id);
    database.delete(MySQLiteHelper.TABLE_COMMENTS, MySQLiteHelper.COLUMN_ID
    + " = " + id, null);
    }

    public List getAllComments() {
    List comments = new ArrayList();
    Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
    allColumns, null, null, null, null, null);
    cursor.moveToFirst();
    while (!cursor.isAfterLast()) {
    Comment comment = cursorToComment(cursor);
    comments.add(comment);
    cursor.moveToNext();
    }
    // Make sure to close the cursor
    cursor.close();
    return comments;
    }

    private Comment cursorToComment(Cursor cursor) {
    Comment comment = new Comment();
    comment.setId(cursor.getLong(0));
    comment.setComment(cursor.getString(1));
    return comment;
    }
    }

  • Change xml file

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

    <LinearLayout
    android:id="@+id/group"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <Button
    android:id="@+id/add"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Add New"
    android:onClick="onClick"/>

    <Button
    android:id="@+id/delete"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Delete First"
    android:onClick="onClick"/>

    </LinearLayout>

    <ListView
    android:id="@android:id/list"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/hello" />

    </LinearLayout>

  • Change your TestDatabaseActivity class. to the following. We use here a ListActivity for displaying the data.

  • import java.util.List;
    import java.util.Random;

    import android.app.ListActivity;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.ArrayAdapter;

    public class TestDatabaseActivity extends ListActivity {
    private CommentsDataSource datasource;

    @Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    datasource = new CommentsDataSource(this);
    datasource.open();

    List values = datasource.getAllComments();

    // Use the SimpleCursorAdapter to show the
    // elements in a ListView
    ArrayAdapter adapter = new ArrayAdapter(this,
    android.R.layout.simple_list_item_1, values);
    setListAdapter(adapter);
    }

    // Will be called via the onClick attribute
    // of the buttons in main.xml
    public void onClick(View view) {
    @SuppressWarnings("unchecked")
    ArrayAdapter adapter = (ArrayAdapter) getListAdapter();
    Comment comment = null;
    switch (view.getId()) {
    case R.id.add:
    String[] comments = new String[] { "Cool", "Very nice", "Hate it" };
    int nextInt = new Random().nextInt(3);
    // Save the new comment to the database
    comment = datasource.createComment(comments[nextInt]);
    adapter.add(comment);
    break;
    case R.id.delete:
    if (getListAdapter().getCount() > 0) {
    comment = (Comment) getListAdapter().getItem(0);
    datasource.deleteComment(comment);
    adapter.remove(comment);
    }
    break;
    }
    adapter.notifyDataSetChanged();
    }

    @Override
    protected void onResume() {
    datasource.open();
    super.onResume();
    }

    @Override
    protected void onPause() {
    datasource.close();
    super.onPause();
    }

    }

    Conclusion

    In onCreate() Method create two methods name -

  • openAndQueryDatabase()
  • displayResultList()
  • 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();
    }

    }

    how do I display the results in a ListView.
    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(this,
    android.R.layout.simple_list_item_1, results));
    getListView().setTextFilterEnabled(true);

    }

    About these ads
    Categories: Uncategorized
    1. November 15, 2012 at 9:36 am

      How can I get the id from the table on clicking on a list item as list item shows the name not the id.

      • February 26, 2013 at 9:40 am

        Thr cursor.

    1. No trackbacks yet.

    Leave a Reply

    Fill in your details below or click an icon to log in:

    WordPress.com Logo

    You are commenting using your WordPress.com account. Log Out / Change )

    Twitter picture

    You are commenting using your Twitter account. Log Out / Change )

    Facebook photo

    You are commenting using your Facebook account. Log Out / Change )

    Google+ photo

    You are commenting using your Google+ account. Log Out / Change )

    Connecting to %s

    Follow

    Get every new post delivered to your Inbox.

    %d bloggers like this: