1. 使用Preference来保存首选项数据
在res/xml下建preference的xml文件
用到的xml的tag： PreferenceScreen PreferenceCategory CheckBoxPreference EditTextPreference RingtonePreference
其中 PreferenceScreen 中的内容显示在同一个界面里， PreferenceScreen 嵌入 PreferenceScreen 可以放置一个入口进入另一个界面；
PreferenceCategory 对首选项内容进行分类（视觉上的，实际调用感觉没区别）；
每个首选项都有一个键值 android:key 跟View的id类似的识别作用；
public class MyPrefAty extends PreferenceActivity { @Override protected void onCreate ( Bundle savedInstanceState ) { super . onCreate ( savedInstanceState ); PreferenceManager preferenceManager = getPreferenceManager (); preferenceManager . setSharedPreferencesName ( "MySelfdefinePrefName" ); addPreferencesFromResource ( R . xml . myapppreferences ); } }
继承自 PreferenceActivity ，从xml文件加载首选项界面，并且重命名该首选项的名称
用到的类： PreferenceManager
用到的方法： getPreferenceManager () setSharedPreferencesName ( "MySelfdefinePrefName" ) addPreferencesFromResource ( R . xml . myapppreferences )
public void onClickDisplay ( View view ) { // SharedPreferences sharedPreferences = getSharedPreferences("com.example.administrator.mypreference_preferences", MODE_PRIVATE); SharedPreferences sharedPreferences = getSharedPreferences ( "MySelfdefinePrefName" , MODE_PRIVATE ); Toast . makeText ( getBaseContext (), sharedPreferences . getString ( "editTextPref" , "" ), Toast . LENGTH_SHORT ). show (); } public void onClickModify ( View view ) { //SharedPreferences sharedPreferences = getSharedPreferences("com.example.administrator.mypreference_preferences", MODE_PRIVATE); SharedPreferences sharedPreferences = getSharedPreferences ( "MySelfdefinePrefName" , MODE_PRIVATE ); SharedPreferences . Editor editor = sharedPreferences . edit (); editor . putString ( "editTextPref" , (( EditText ) findViewById ( R . id . txtString )). getText (). toString ()); editor . commit (); }
用到的类： SharedPreferences SharedPreferences . Editor
用到的方法： getSharedPreferences ( "MySelfdefinePrefName" , MODE_PRIVATE ) edit () putString（） commit ()
关键： getSharedPreferences（） 的第一个参数是对应首选项的xml的名称，默认是 “包名+_preferencens”，由此获得相应的首选项。修改首选项中的值 需要用到 SharedPreferences . Editor
2. 数据保存到内部存储
public class FileSave extends Activity { EditText editText; static final int READ_BLOCK_SIZE = 100; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.myfilesavelayout); editText = (EditText) findViewById(R.id.edittextFile); } public void onClickLoad(View v) { try { FileInputStream fileInputStream = openFileInput("textfile.txt"); InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream); char[] inputBuffer = new char[READ_BLOCK_SIZE]; String s = ""; int charRead; while ((charRead = inputStreamReader.read(inputBuffer)) > 0) { String readString = String.copyValueOf(inputBuffer, 0, charRead); s += readString; } editText.setText(s); Toast.makeText(getBaseContext(), "File Load Successfully.", Toast.LENGTH_SHORT).show(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } public void onClickSave(View view) { String string = editText.getText().toString(); try { FileOutputStream fileOutputStream = openFileOutput("textfile.txt", MODE_WORLD_READABLE); OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream); outputStreamWriter.write(string); outputStreamWriter.flush(); outputStreamWriter.close(); Toast.makeText(getBaseContext(), "File Save Successfully", Toast.LENGTH_SHORT).show(); editText.setText(""); } catch (IOException e) { e.printStackTrace(); } } }
用到的类： FileInputStream InputStreamReader FileOutputStream OutputStreamWriter
用到的方法： openFileInput ( "textfile.txt" ) read ( inputBuffer ) copyValueOf ( inputBuffer , 0 , charRead ) openFileOutput ( "textfile.txt" , MODE_WORLD_READABLE ) write ( string ) flush () close ()
关键点： openFileOutput ( "textfile.txt" , MODE_WORLD_READABLE ) 和 openFileInput ( "textfile.txt" ) 都是使用相对路径，即内部存储的路径，只需要自定义文件名。
3. 保存数据到SD卡（外部存储）
public class SdSave extends Activity { EditText editText; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.mysdlayout); editText = (EditText) findViewById(R.id.SDedittextFile); } public void onClickSaveSD(View view) { String string = editText.getText().toString(); try { File sdCard = Environment.getExternalStorageDirectory(); File directory = new File(sdCard.getAbsolutePath() + "/MyFiles"); directory.mkdir(); File file = new File(directory, "textfile.txt"); FileOutputStream fileOutputStream = new FileOutputStream(file); OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream); outputStreamWriter.write(string); outputStreamWriter.flush(); outputStreamWriter.close(); } catch (IOException e) { e.printStackTrace(); } Toast.makeText(getBaseContext(), "Save In SD successfully!", Toast.LENGTH_SHORT).show(); editText.setText(""); } public void onClickLoadSD(View view) { try { File sdCard = Environment.getExternalStorageDirectory(); File directory = new File(sdCard.getAbsolutePath() + "/MyFiles"); File file = new File(directory, "textfile.txt"); FileInputStream fileInputStream = new FileInputStream(file); InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream); char[] inputBuffer = new char[100]; String s = ""; int charRead; while ((charRead = inputStreamReader.read(inputBuffer)) > 0) { String readString = String.copyValueOf(inputBuffer, 0, charRead); s += readString; inputBuffer = new char[100]; } editText.setText(s); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } }
用到的类： File Environment FileOutputStream OutputStreamWriter FileInputStream InputStreamReader
用到的方法： getExternalStorageDirectory () getAbsolutePath () mkdir () write ( string ) flush () close () read ( inputBuffer ) copyValueOf ( inputBuffer , 0 , charRead )
关键在于用 getExternalStorageDirectory () 和 getAbsolutePath () 获得SD卡完整的路径（还需加上自定义的文件夹名和文件名）
4.使用数据库
public class DBAdapter { static final String KEY_ROWID = "_id"; static final String KEY_NAME = "name"; static final String KEY_EMAIL = "email"; static final String TAG = "DBAdapter"; static final String DATABASE_NAME = "MyDB3"; static final String DATABASE_TABLE = "contacts"; static final int DATABASE_VERSON = 1; static final String DATABASE_CREATE = "create table contacts (_id integer primary key autoincrement,name text not null,email text not null);"; final Context context; DatabaseHelper DBHelper; SQLiteDatabase db; public DBAdapter(Context context){ this.context = context; DBHelper = new DatabaseHelper(context); } private static class DatabaseHelper extends SQLiteOpenHelper{ DatabaseHelper(Context context){ super(context, DATABASE_NAME, null, DATABASE_VERSON); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL(DATABASE_CREATE); } @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 contacts"); onCreate(db); } } public DBAdapter open() throws SQLException{ db = DBHelper.getWritableDatabase(); //db = DBHelper.getReadableDatabase(); return this; } public void close(){ DBHelper.close(); } public long inserContacts(String name,String email){ ContentValues initialValues = new ContentValues(); initialValues.put(KEY_NAME,name); initialValues.put(KEY_EMAIL, email); return db.insert(DATABASE_TABLE,null,initialValues); } public boolean deleteContact(long rowId){ return db.delete(DATABASE_TABLE,KEY_ROWID+"="+rowId,null)>0; } public Cursor getAllContacts(){ return db.query(DATABASE_TABLE,new String[]{KEY_ROWID,KEY_NAME,KEY_EMAIL},null,null,null,null,null); } public Cursor getContact(long rowId) throws SQLException{ Cursor cursor = db.query(true,DATABASE_TABLE,new String[]{KEY_ROWID,KEY_NAME,KEY_EMAIL},KEY_ROWID +"="+rowId,null,null,null,null,null); if (cursor!=null) cursor.moveToFirst(); return cursor; } public boolean updateContact(long rowId,String name,String email){ ContentValues args = new ContentValues(); args.put(KEY_NAME,name); args.put(KEY_EMAIL,email); return db.update(DATABASE_TABLE,args,KEY_ROWID+"="+rowId,null)>0; }}
概述：创建一个辅助类来封装访问数据的复杂性（即方法）
用到的类： SQLiteDatabase SQLiteOpenHelper ContentValues Cursor
用到的方法： onUpgrade ( SQLiteDatabase db , int oldVersion , int newVersion ) getWritableDatabase () close () put ( KEY_NAME , name ) insert ( DATABASE_TABLE , null , initialValues ) delete ( DATABASE_TABLE , KEY_ROWID + "=" + rowId , null ) query ( DATABASE_TABLE , new String []{ KEY_ROWID , KEY_NAME , KEY_EMAIL }, null , null , null , null , null ) update ( DATABASE_TABLE , args , KEY_ROWID + "=" + rowId , null )
核心： SQLiteOpenHelper 是个安卓SQL的辅助类，用来处理数据库的创建和版本管理 ,需要重写它的onCreate（）和onUpgrade()方法。 onCreate（）在所需数据库不存在的时候被调用来创建一个新的数据库， onUpgrade()在数据库需要升级的时候被调用，取决于数据库的版本号码变化。（e.g. 将上面代码中的 DATABASE_VERSON从1改到2 ，再次运行程序的时候onUpgrade()就会被调用 ）
编程方式使用数据库——
public class MainActivity extends Activity { DBAdapter dbAdapter; TextView textView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); textView = (TextView) findViewById(R.id.showInfo); dbAdapter = new DBAdapter(this); try { dbAdapter.open(); } catch (SQLException e) { e.printStackTrace(); } long id = dbAdapter.inserContacts("Li XiaoMing","997654321@qq.com"); id = dbAdapter.inserContacts("Bruce","lixiaoming@gmail.com"); dbAdapter.close(); } public void ShowAllcontacts(View view) { try { dbAdapter.open(); Cursor cursor = dbAdapter.getAllContacts(); String s = ""; if (cursor.moveToFirst()) { do { s += "id: " + cursor.getString(0) + " Name: " + cursor.getString(1) + " Email: " + cursor.getString(2) + "\n"; } while (cursor.moveToNext()); textView.setText(s); } dbAdapter.close(); } catch (SQLException e) { e.printStackTrace(); } } public void ShowOneContact(View view) { EditText editText = (EditText) findViewById(R.id.edittext_id); int id = Integer.parseInt(editText.getText().toString()); // Toast.makeText(getBaseContext(),Integer.toString(id),Toast.LENGTH_SHORT).show(); try { dbAdapter.open(); Cursor cursor = dbAdapter.getContact(id); if (cursor.moveToFirst()) textView.setText("id: " + cursor.getString(0) + " Name: " + cursor.getString(1) + " Email: " + cursor.getString(2) + "\n"); else Toast.makeText(getBaseContext(), "Contact Not Found", Toast.LENGTH_SHORT).show(); } catch (SQLException e) { e.printStackTrace(); } dbAdapter.close(); } public void UpdateContact(View view) { EditText editText = (EditText) findViewById(R.id.edittext_id); int id = Integer.parseInt(editText.getText().toString()); try { dbAdapter.open(); } catch (SQLException e) { e.printStackTrace(); } if (dbAdapter.updateContact(id, "Charley", "12332@outook.com")) Toast.makeText(getBaseContext(), "update Success", Toast.LENGTH_SHORT).show(); else Toast.makeText(getBaseContext(), "update failure", Toast.LENGTH_SHORT).show(); dbAdapter.close(); } public void DeleteContact(View view) { EditText editText = (EditText) findViewById(R.id.edittext_id); int id = Integer.parseInt(editText.getText().toString()); try { dbAdapter.open(); } catch (SQLException e) { e.printStackTrace(); } if (dbAdapter.deleteContact(id)) Toast.makeText(getBaseContext(), "Delete Success", Toast.LENGTH_SHORT).show(); else Toast.makeText(getBaseContext(), "Delete failure", Toast.LENGTH_SHORT).show(); dbAdapter.close(); }}
用到的类： Cursor DBAdapter(自定义的类)
用到的方法： moveToFirst () moveToNext () getString ( )
分析：使用时主要使用自定义的 DBAdapter 类进行处理数据，其中 Cursor 作为检索返回的数据的类型（类似一个数组集合）
以上的方法的数据库是在运行的时候被创建的，但有时程序可能需要使用现有的数据库或者导入预创建好的数据库。
那么，如何使用于创建好的数据库——
首先，介绍一个可以用来查看和编辑SQLite数据库的软件——sqlitebrowser—— 。
接着，简单介绍一下安卓使用的 SQLite 数据库的特殊之处：
如果在程序中创建一个DB，导出后使用进行sqlitebrowser查看——发现，有2个额外的表 android_metadata和sqlite_squence
其中android_metadata用来定义使用的语言，可以删除（虽然有的博客说不行，但我亲测是可以的）
sqlite_squence似乎是来记录主要表的信息（项的数量），并且无法删除
易出Bug的地方：
由 sqlitebrowser新建一个DB，会将版本默认为是0，在上面的代码中 DATABASE_VERSON 设置为1，因此如果直接导入新建的这个DB，会出现错误（程序崩溃...查了好久的bug...）
在以下的地方进行修改版本号
将DB文件放入\app\src\main\assets文件夹
代码：
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); textView = (TextView) findViewById(R.id.showInfo); dbAdapter = new DBAdapter(this); try { String destPath = "/data/data/" + getPackageName() + "/databases"; Toast.makeText(getBaseContext(), destPath, Toast.LENGTH_SHORT).show(); File file = new File(destPath); if (!file.exists()) { file.mkdirs(); file.createNewFile(); CopyDB(getBaseContext().getAssets().open("test2"), new FileOutputStream(destPath + "/MyDB3")); } } catch (IOException e) { e.printStackTrace(); } } public void CopyDB(InputStream inputStream, OutputStream outputStream) throws IOException { byte[] buffer = new byte[1024]; int length; while ((length = inputStream.read(buffer)) > 0) { outputStream.write(buffer, 0, length); } Toast.makeText(getBaseContext(), "Copy Success", Toast.LENGTH_SHORT).show(); inputStream.close(); outputStream.close(); }
用到的类： File FileOutputStream InputStream
用到的方法： getPackageName () mkdirs () createNewFile () write ( buffer , 0 , length )
分析： 将assets里的DB文件拷贝到内部存储的databases文件夹里；DB文件至多只会被拷贝一次，因为是在判断databases文件夹是否存在之后才进行拷贝，避免重复覆盖DB数据。