Notepad v3
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NotesDbAdapter.java
/*
* Copyright (C) 2008 Google Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); you may not * use this file except in compliance with the License. You may obtain a copy of * the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations under * the License. */
package com.android.demo.notepad3;
import android.content.ContentValues; import android.content.Context; import android.database.Cursor; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.util.Log;
/**
* Simple notes database access helper class. Defines the basic CRUD operations * for the notepad example, and gives the ability to list all notes as well as * retrieve or modify a specific note. * * This has been improved from the first version of this tutorial through the * addition of better error handling and also using returning a Cursor instead * of using a collection of inner classes (which is less scalable and not * recommended). */
public class NotesDbAdapter {
public static final String KEY_TITLE = "title"; public static final String KEY_BODY = "body"; public static final String KEY_ROWID = "_id";
private static final String TAG = "NotesDbAdapter";
private DatabaseHelper mDbHelper;
private SQLiteDatabase mDb;
// SQLiteDatabase exposes methods to execute SQLite queries.
/**
* Database creation sql statement
*/
private static final String DATABASE_CREATE =
"create table notes (_id integer primary key autoincrement, "
+ "title text not null, body text not null);";
// DATABASE_CREATE is an SQLite query used to create a table called 'notes'
// with id, title, and body as its fields.
private static final String DATABASE_NAME = "data"; private static final String DATABASE_TABLE = "notes"; private static final int DATABASE_VERSION = 2;
private final Context mCtx;
private static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(DATABASE_CREATE);
}
// The onCreate method is used to create the database for the
// first time, where initial population of the tables happen
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS notes");
onCreate(db);
}
}
/**
* Constructor - takes the context to allow the database to be
* opened/created
*
* @param ctx the Context within which to work
*/
public NotesDbAdapter(Context ctx) {
this.mCtx = ctx;
}
//Context is a package found under android.content
//It has implementations to access application specific resources
//such as launching activities and broadcasting messages.
/**
* Open the notes database. If it cannot be opened, try to create a new
* instance of the database. If it cannot be created, throw an exception to
* signal the failure
*
* @return this (self reference, allowing this to be chained in an
* initialization call)
* @throws SQLException if the database could be neither opened or created
*/
public NotesDbAdapter open() throws SQLException {
mDbHelper = new DatabaseHelper(mCtx);
// The DatabaseHelper class is a sub class of SQLiteOpenHelper class
// which takes care of opening or creating the database.
// mCtx is an object of the Context. It acts as a parameter to the
// DatabaseHelper method.
mDb = mDbHelper.getWritableDatabase();
// getWriteableDatabase is a member function of SQLiteOpenHelper
// class which creates/opens a database used for reading/writing.
// mDb is a SQLiteDatabase object.
return this;
}
public void close() {
mDbHelper.close();
}
// the close method closes any open databases.
/**
* Create a new note using the title and body provided. If the note is
* successfully created return the new rowId for that note, otherwise return
* a -1 to indicate failure.
*
* @param title the title of the note
* @param body the body of the note
* @return rowId or -1 if failed
*/
public long createNote(String title, String body) {
ContentValues initialValues = new ContentValues();
// The ContentValues class is class from android.content.ContentValues
// which is used to store values.
// The contentValues() method is used create a set of values
// with default initialisation.
initialValues.put(KEY_TITLE, title);
initialValues.put(KEY_BODY, body);
//The put() method is used to add values through the object.
return mDb.insert(DATABASE_TABLE, null, initialValues);
// mDb invokes the the method insert() from the SQLiteDatabase class
// which lets us insert values into the DATABASE_TABLE = "notes" which is
// created at the same time.
}
/**
* Delete the note with the given rowId
*
* @param rowId id of note to delete
* @return true if deleted, false otherwise
*/
public boolean deleteNote(long rowId) {
return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0; } // mDb invokes the delete() method of the SQLiteDatabase class which // takes appropriate parameters to delete a particular row. // *warning* passing null as the second parameter will delete // all the rows.
/**
* Return a Cursor over the list of all notes in the database
*
* @return Cursor over all notes
*/
public Cursor fetchAllNotes() {
return mDb.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_TITLE,
KEY_BODY}, null, null, null, null, null);
}
// The method query() returns a Cursor object. The Cursor object provides
// read/write access to the information provided by the SQLite query.
/**
* Return a Cursor positioned at the note that matches the given rowId
*
* @param rowId id of note to retrieve
* @return Cursor positioned to matching note, if found
* @throws SQLException if note could not be found/retrieved
*/
public Cursor fetchNote(long rowId) throws SQLException {
Cursor mCursor =
mDb.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
KEY_TITLE, KEY_BODY}, KEY_ROWID + "=" + rowId, null,
null, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
/**
* Update the note using the details provided. The note to be updated is
* specified using the rowId, and it is altered to use the title and body
* values passed in
*
* @param rowId id of note to update
* @param title value to set note title to
* @param body value to set note body to
* @return true if the note was successfully updated, false otherwise
*/
public boolean updateNote(long rowId, String title, String body) {
ContentValues args = new ContentValues();
args.put(KEY_TITLE, title);
args.put(KEY_BODY, body);
return mDb.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
// The update() method is invoked which updates the database.
// The third parameter takes the row Id which needs to be updated
// It returns the 'number' of rows updated.
}
}
Notepadv3.java
/*
* Copyright (C) 2008 Google Inc. * * Licensed under the Apache License, Version 2.0 (the "License")savedInstanceState; * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */
package com.android.demo.notepad3;
import android.app.ListActivity; import android.content.Intent; import android.database.Cursor; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.widget.ListView; import android.widget.SimpleCursorAdapter;
public class Notepadv3 extends ListActivity {
private static final int ACTIVITY_CREATE=0; private static final int ACTIVITY_EDIT=1; private static final int INSERT_ID = Menu.FIRST; private static final int DELETE_ID = Menu.FIRST + 1;
private NotesDbAdapter mDbHelper;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// super keyword is used to invoke the base class constructor
setContentView(R.layout.notes_list);
// setContentView() method is used set the content from the layout
// resource which in this case is /res/layout/notes_list.xml
mDbHelper = new NotesDbAdapter(this);
mDbHelper.open();
// open() method is invoked declared in the NotesDbAdapter class.
fillData();
}
private void fillData() {
Cursor notesCursor = mDbHelper.fetchAllNotes();
startManagingCursor(notesCursor);
// Create an array to specify the fields we want to display in the list (only TITLE)
String[] from = new String[]{NotesDbAdapter.KEY_TITLE};
// and an array of the fields we want to bind those fields to (in this case just text1)
int[] to = new int[]{R.id.text1};
// Now create a simple cursor adapter and set it to display
SimpleCursorAdapter notes =
new SimpleCursorAdapter(this, R.layout.notes_row, notesCursor, from, to);
// Creates an object of the SimpleCursorAdapter with parametrised
// constructors.
setListAdapter(notes);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
menu.add(0, INSERT_ID, 0, R.string.menu_insert);
menu.add(0, DELETE_ID, 0, R.string.menu_delete);
return true;
}
// onCreateOptionsMenu is a class which takes in a parameter of type
// Menu from the package android.view.Menu, which acts as an interface
// for managing menus.
// the add() method defined in the class Menu uses the values declared
// in the xml file strings.xml
@Override
public boolean onMenuItemSelected(int featureId, MenuItem item) {
switch(item.getItemId()) {
case INSERT_ID:
createNote();
return true;
case DELETE_ID:
mDbHelper.deleteNote(getListView().getSelectedItemId());
fillData();
return true;
}
// Depending on the Menu selected, item is either created using the
// method createnote() or deleted by calling the method deleteNote()
// declared in NotesDbAdapter.java
return super.onMenuItemSelected(featureId, item);
}
private void createNote() {
Intent i = new Intent(this, NoteEdit.class);
startActivityForResult(i, ACTIVITY_CREATE);
}
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
super.onListItemClick(l, v, position, id);
Intent i = new Intent(this, NoteEdit.class);
i.putExtra(NotesDbAdapter.KEY_ROWID, id);
startActivityForResult(i, ACTIVITY_EDIT);
}
@Override
protected void onActivityResult(int requestCode, int resultCode,
Intent intent) {
super.onActivityResult(requestCode, resultCode, intent);
fillData();
}
}
NoteEdit.java
/*
* Copyright (C) 2008 Google Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */
package com.android.demo.notepad3;
import android.app.Activity; import android.database.Cursor; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.EditText;
public class NoteEdit extends Activity {
private EditText mTitleText;
private EditText mBodyText; private Long mRowId; private NotesDbAdapter mDbHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// invokes the base class (Activity) constructor.
mDbHelper = new NotesDbAdapter(this);
mDbHelper.open();
// opens the database 'notes'
setContentView(R.layout.note_edit);
mTitleText = (EditText) findViewById(R.id.title);
mBodyText = (EditText) findViewById(R.id.body);
Button confirmButton = (Button) findViewById(R.id.confirm);
// creates an instance of the class Button.
mRowId = savedInstanceState != null ? savedInstanceState.getLong(NotesDbAdapter.KEY_ROWID)
: null;
if (mRowId == null) { Bundle extras = getIntent().getExtras(); mRowId = extras != null ? extras.getLong(NotesDbAdapter.KEY_ROWID) : null; }
populateFields();
confirmButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
setResult(RESULT_OK);
finish();
}
});
}
private void populateFields() {
if (mRowId != null) {
Cursor note = mDbHelper.fetchNote(mRowId);
// the method fetchNote() would return the position of the note
// at mRowId
startManagingCursor(note);
mTitleText.setText(note.getString(
note.getColumnIndexOrThrow(NotesDbAdapter.KEY_TITLE)));
mBodyText.setText(note.getString(
note.getColumnIndexOrThrow(NotesDbAdapter.KEY_BODY)));
}
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putLong(NotesDbAdapter.KEY_ROWID, mRowId);
}
@Override
protected void onPause() {
super.onPause();
saveState();
}
@Override
protected void onResume() {
super.onResume();
populateFields();
}
private void saveState() {
String title = mTitleText.getText().toString();
String body = mBodyText.getText().toString();
if (mRowId == null) {
long id = mDbHelper.createNote(title, body);
if (id > 0) {
mRowId = id;
}
} else {
mDbHelper.updateNote(mRowId, title, body);
}
}
}
