android中的保存数据方法

android中保存数据的方式有

1，云存储（网络保存），

2，本地SharedPreferences保存少量数据，

3，本地文件流保存，

4，本地数据库保存。

下面讲的第2，3，4点；

2.SharedPreferences为程序持久化保存少量值：

<span style="font-size:18px;">获取SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);</span>

<span style="font-size:18px;">或者SharedPreferences sharedPref = getSharedPreferences(name, mode) 如果该文件不存在会自动创建</span>

<span style="font-size:18px;"></span>

<span style="font-size:18px;">写入， SharedPreferences sharedPref =  getActivity().getPreferences(Context.MODE_PRIVATE);  SharedPreferences.Editor editor = sharedPref.edit();  editor.putInt(getString(R.string.saved_high_score), newHighScore);  editor.commit();</span>

<span style="font-size:18px;">读取， SharedPreferences sharedPref =  getActivity().getPreferences(Context.MODE_PRIVATE);</span>

<span style="font-size:18px;"><span style="white-space:pre"></span>int defaultValue =getResources().getInteger(R.string.saved_high_score_default);</span>

<span style="font-size:18px;"><span style="white-space:pre"></span>long highScore = sharedPref.getInt(getString(R.string.saved_high_score),defaultValue);</span>

3.本地文件存储
存储路径又分为内部和外部存储。早期的手机设备区分的很明显。现在的手机可能会将一个存储空间直接划分成这两个部分。内部存储，通常可用的，不用担心它悬挂，是app安装的路径（默认的，当然可以指定app的安装路径android:installLocation），当app卸载后，app相关的文件会随之删除。当你想要用户和其他app无法访问该app的文件的时候可以考虑设置路径为这个。

内部路径，getFilesDir()，getCacheDir()

外部存储，通常是不可用的，因为用户会手动移除或者悬挂，所有在访问之前要判断外部存储的状态。

<span style="font-size:18px;">public boolean isExternalStorageWritable() {</span>

<span style="font-size:18px;">String state =Environment.getExternalStorageState();</span>

<span style="font-size:18px;">if(Environment.MEDIA_MOUNTED.equals(state)) {</span>

<span style="font-size:18px;"><span style="white-space:pre"></span>return true;</span>

<span style="font-size:18px;">}</span>

<span style="font-size:18px;">return false;</span>

<span style="font-size:18px;">}</span>

存储在这里的文件是可以被任何人和任何app访问的，而且当app卸载后，该文件不会自动删除，容易造成垃圾文件。

使用外部存储空间，需要添加权限，<manifest ...> <uses-permission
android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> ...
</manifest>

4.SQLiteOpenHelper数据库存储;步骤如下，

<span style="font-size:18px;">a.自定义类继承SQLiteOpenHelper  public class FeedReaderDbHelper extends SQLiteOpenHelper {    // If you change the database schema, you must increment the database version.    public static final int DATABASE_VERSION = 1;    public static final String DATABASE_NAME = "FeedReader.db";    public FeedReaderDbHelper(Context context) {        super(context, DATABASE_NAME, null, DATABASE_VERSION);    }    public void onCreate(SQLiteDatabase db) {        db.execSQL(SQL_CREATE_ENTRIES);    }    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {        // This database is only a cache for online data, so its upgrade policy is        // to simply to discard the data and start over        db.execSQL(SQL_DELETE_ENTRIES);        onCreate(db);    }    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {        onUpgrade(db, oldVersion, newVersion);    }}</span>

<span style="font-size:18px;">private static final String TEXT_TYPE = " TEXT";private static final String COMMA_SEP = ",";private static final String SQL_CREATE_ENTRIES =    "CREATE TABLE " + FeedEntry.TABLE_NAME + " (" +    FeedEntry._ID + " INTEGER PRIMARY KEY," +    FeedEntry.COLUMN_NAME_ENTRY_ID + TEXT_TYPE + COMMA_SEP +    FeedEntry.COLUMN_NAME_TITLE + TEXT_TYPE + COMMA_SEP +    ... // Any other options for the CREATE command    " )";private static final String SQL_DELETE_ENTRIES =    "DROP TABLE IF EXISTS " + FeedEntry.TABLE_NAME;        public final class FeedReaderContract {    // To prevent someone from accidentally instantiating the contract class,    // give it an empty constructor.    public FeedReaderContract() {}    Inner class that defines the table contents     public static abstract class FeedEntry implements BaseColumns {        public static final String TABLE_NAME = "entry";        public static final String COLUMN_NAME_ENTRY_ID = "entryid";        public static final String COLUMN_NAME_TITLE = "title";        public static final String COLUMN_NAME_SUBTITLE = "subtitle";        ...    }}</span>

下面的增删查改都需要在子线程中进行;

<span style="font-size:18px;">b.写入数据，// Gets the data repository in write modeSQLiteDatabase db = mDbHelper.getWritableDatabase();// Create a new map of values, where column names are the keysContentValues values = new ContentValues();values.put(FeedEntry.COLUMN_NAME_ENTRY_ID, id);values.put(FeedEntry.COLUMN_NAME_TITLE, title);values.put(FeedEntry.COLUMN_NAME_CONTENT, content);// Insert the new row, returning the primary key value of the new rowlong newRowId;newRowId = db.insert(         FeedEntry.TABLE_NAME,         FeedEntry.COLUMN_NAME_NULLABLE,         values);         c.读出数据，SQLiteDatabase db = mDbHelper.getReadableDatabase();// Define a projection that specifies which columns from the database// you will actually use after this query.String[] projection = {    FeedEntry._ID,    FeedEntry.COLUMN_NAME_TITLE,    FeedEntry.COLUMN_NAME_UPDATED,    ...    };// How you want the results sorted in the resulting CursorString sortOrder =    FeedEntry.COLUMN_NAME_UPDATED + " DESC";Cursor c = db.query(    FeedEntry.TABLE_NAME,  // The table to query    projection,                               // The columns to return    selection,                                // The columns for the WHERE clause    selectionArgs,                            // The values for the WHERE clause    null,                                     // don't group the rows    null,                                     // don't filter by row groups    sortOrder                                 // The sort order    );    d.删除数据，// Define 'where' part of query.String selection = FeedEntry.COLUMN_NAME_ENTRY_ID + " LIKE ?";// Specify arguments in placeholder order.String[] selectionArgs = { String.valueOf(rowId) };// Issue SQL statement.db.delete(table_name, selection, selectionArgs);e.更新数据，SQLiteDatabase db = mDbHelper.getReadableDatabase();// New value for one columnContentValues values = new ContentValues();values.put(FeedEntry.COLUMN_NAME_TITLE, title);// Which row to update, based on the IDString selection = FeedEntry.COLUMN_NAME_ENTRY_ID + " LIKE ?";String[] selectionArgs = { String.valueOf(rowId) };int count = db.update(    FeedReaderDbHelper.FeedEntry.TABLE_NAME,    values,    selection,    selectionArgs);</span>

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