【IT168 技术文档】这个实例主要是对SDK中的Notepadv2Solution的修改和完善，因为本人在使用该sample发现一些错误和缺陷,主要是空指针异常。(1)Notepadv1.java：

package com.google.android.demo.notepad1;

import android.app.ListActivity;

import android.content.Intent;

import android.database.Cursor;

import android.os.Bundle;

import android.view.Menu;

import android.view.View;

import android.view.Menu.Item;

import android.widget.ListView;

import android.widget.SimpleCursorAdapter;

public class Notepadv1 extends ListActivity {

public static final int INSERT_ID = Menu.FIRST;

private static final int EXIT_ID = 0;

private static final int DELETE_ID = Menu.FIRST + 1;

private static final int ACTIVITY_EDIT = 1;

private static final int ACTIVITY_CREATE = 0;

private NotesDbAdapter mDbHelper;

private Cursor c;

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

@Override

public void onCreate(Bundle icicle) {

super.onCreate(icicle);

setContentView(R.layout.notepad_list);

mDbHelper = new NotesDbAdapter(this);

mDbHelper.open();

fillData();

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

boolean result = super.onCreateOptionsMenu(menu);

menu.add(0, INSERT_ID, R.string.menu_insert);

menu.add(0, EXIT_ID, R.string.exit_notes);

menu.add(0, DELETE_ID, R.string.menu_delete);

return result;

}

@Override

public boolean onOptionsItemSelected(Item item) {

switch (item.getId()) {

case INSERT_ID:

createNote();

return true;

case EXIT_ID:

finish();

return true;

case DELETE_ID:

mDbHelper.deleteNote(getListView().getSelectedItemId());

fillData();

return true;

}

return super.onOptionsItemSelected(item);

}

private void createNote() {

Intent i = new Intent(this, NoteEdit.class);

startSubActivity(i, ACTIVITY_CREATE);

}

private void fillData() {

// Get all of the notes from the database and create the item list

c = mDbHelper.fetchAllNotes();

startManagingCursor(c);

String[] from = new String[] { NotesDbAdapter.KEY_TITLE };

int[] to = new int[] { R.id.text1 };

// Now create an array adapter and set it to display using our row

SimpleCursorAdapter notes =

new SimpleCursorAdapter(this, R.layout.notes_row, c, from, to);

setListAdapter(notes);

}

@Override

protected void onListItemClick(ListView l, View v, int position, long id) {

super.onListItemClick(l, v, position, id);

c.moveTo(position);

Intent i = new Intent(this, NoteEdit.class);

i.putExtra(NotesDbAdapter.KEY_ROWID, id);

i.putExtra(NotesDbAdapter.KEY_TITLE, c.getString(

c.getColumnIndex(NotesDbAdapter.KEY_TITLE)));

i.putExtra(NotesDbAdapter.KEY_BODY, c.getString(

c.getColumnIndex(NotesDbAdapter.KEY_BODY)));

startSubActivity(i, ACTIVITY_EDIT);

}

@Override

protected void onActivityResult(int requestCode, int resultCode, String data, Bundle extras) {

super.onActivityResult(requestCode, resultCode, data, extras);

switch(requestCode) {

case ACTIVITY_CREATE:

if(extras == null)

break;

String title = extras.getString(NotesDbAdapter.KEY_TITLE);

String body = extras.getString(NotesDbAdapter.KEY_BODY);

mDbHelper.createNote(title, body);

fillData();

break;

case ACTIVITY_EDIT:

if(extras == null)

break;

Long rowId = extras.getLong(NotesDbAdapter.KEY_ROWID);

if (rowId != null) {

String editTitle = extras.getString(NotesDbAdapter.KEY_TITLE);

String editBody = extras.getString(NotesDbAdapter.KEY_BODY);

mDbHelper.updateNote(rowId, editTitle, editBody);

}

fillData();

break;

}

}

}

说明：

此activity主要是将为创建notepad做前期工作的，此外还做收尾工作，将从后台接受过来的数据显示出来。

图示：

(2)NoteEdit.java:

package com.google.android.demo.notepad1;

import android.app.Activity;

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;

@Override

protected void onCreate(Bundle icicle) {

super.onCreate(icicle);

setContentView(R.layout.note_edit);        mTitleText = (EditText) findViewById(R.id.title);

mBodyText = (EditText) findViewById(R.id.body);

Button confirmButton = (Button) findViewById(R.id.confirm);

mRowId = null;

Bundle extras = getIntent().getExtras();

if (extras != null) {

String title = extras.getString(NotesDbAdapter.KEY_TITLE);

String body = extras.getString(NotesDbAdapter.KEY_BODY);

mRowId = extras.getLong(NotesDbAdapter.KEY_ROWID);

if (title != null) {

mTitleText.setText(title);

}

if (body != null) {

mBodyText.setText(body);

}

}        confirmButton.setOnClickListener(new View.OnClickListener() {

public void onClick(View view) {

Bundle bundle = new Bundle();

bundle.putString(NotesDbAdapter.KEY_TITLE, mTitleText.getText().toString());

bundle.putString(NotesDbAdapter.KEY_BODY, mBodyText.getText().toString());

if (mRowId != null) {

bundle.putLong(NotesDbAdapter.KEY_ROWID, mRowId);

}

setResult(RESULT_OK, null, bundle);

finish();

}

});

}

}

说明：

接受前台的命令，开始创建notepad，并将数据传递到前台。注意if (extras != null) 可以可以防止输入数据为空时的空指针异常情况。

图示：

(3)NotesDbAdapter.java:

package com.google.android.demo.notepad1;

import android.content.ContentValues;

import android.content.Context;

import android.database.Cursor;

import android.database.SQLException;

import android.database.sqlite.SQLiteDatabase;

import java.io.FileNotFoundException;

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 DATABASE_CREATE =

"create table notes (_id integer primary key autoincrement, "

+ "title text not null, body text not null);";

private static final String DATABASE_NAME = "data";

private static final String DATABASE_TABLE = "notes";

private static final int DATABASE_VERSION = 2;

private SQLiteDatabase mDb;

private final Context mCtx;

public NotesDbAdapter(Context ctx) {

this.mCtx = ctx;

}

public NotesDbAdapter open() throws SQLException {

try {

mDb = mCtx.openDatabase(DATABASE_NAME, null);

} catch (FileNotFoundException e) {

try {

mDb =

mCtx.createDatabase(DATABASE_NAME, DATABASE_VERSION, 0,

null);

mDb.execSQL(DATABASE_CREATE);

} catch (FileNotFoundException e1) {

throw new SQLException("Could not create database");

}

}

return this;

}

public void close() {

mDb.close();

}

public long createNote(String title, String body) {

ContentValues initialValues = new ContentValues();

initialValues.put(KEY_TITLE, title);

initialValues.put(KEY_BODY, body);

return mDb.insert(DATABASE_TABLE, null, initialValues);

}

public boolean deleteNote(long rowId) {

return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;

}

public Cursor fetchAllNotes() {

return mDb.query(DATABASE_TABLE, new String[] {

KEY_ROWID, KEY_TITLE, KEY_BODY}, null, null, null, null, null);

}

public Cursor fetchNote(long rowId) throws SQLException {

Cursor result = mDb.query(true, DATABASE_TABLE, new String[] {

KEY_ROWID, KEY_TITLE, KEY_BODY}, KEY_ROWID + "=" + rowId, null, null,

null, null);

if ((result.count() == 0) || !result.first()) {

throw new SQLException("No note matching ID: " + rowId);

}

return result;

}

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;

}

}

说明：

数据库和数据库操作在里面。

(4)notepad_list.xml:

android:layout_width="wrap_content"

android:layout_height="wrap_content">

android:layout_width="wrap_content"

android:layout_height="wrap_content"/>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/no_notes"/>

(5)note_edi.xml:

android:orientation="vertical"

android:layout_width="fill_parent"

android:layout_height="fill_parent">

android:layout_width="fill_parent"

android:layout_height="wrap_content">

android:layout_height="wrap_content"

android:text="@string/title" />

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_weight="1"/>

android:layout_height="wrap_content"

android:text="@string/body" />

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:layout_weight="1"

android:scrollbars="vertical" />

android:text="@string/confirm"

android:layout_width="wrap_content"

android:layout_height="wrap_content" />

(6)notes_row.xml:

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

android:layout_width="wrap_content"

android:layout_height="wrap_content"/>

(7)strings.xml:

Notepad v1

No Notes Yet

Add Item

Exit Notepad

Delete Item

Title

Body

Confirm

Edit Note

(8)AndroidManifest.xml:

package="com.google.android.demo.notepad1">