android中的儲存資料方法
阿新 • • 發佈：2019-01-22
android中儲存資料的方式有
1，雲端儲存（網路儲存），
2，本地SharedPreferences儲存少量資料，
3，本地檔案流儲存，
4，本地資料庫儲存。
下面講的第2，3，4點；
2.SharedPreferences為程式持久化儲存少量值：
<span style="font-size:18px;">獲取SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);</span><span style="font-size:18px;">或者SharedPreferences sharedPref = getSharedPreferences(name, mode) 如果該檔案不存在會自動建立</span>
<span style="font-size:18px;">
</span><span style="font-size:18px;">寫入， 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;">讀取， 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>儲存路徑又分為內部和外部儲存。早期的手機裝置區分的很明顯。現在的手機可能會將一個儲存空間直接劃分成 這兩個部分。內部儲存，通常可用的，不用擔心它懸掛，是app安裝的路徑（預設的，當然可以指定 app的安裝路徑android:installLocation），當app解除安裝後，app相關的檔案會隨之刪除。當你想要使用者和其他app無法訪問該app的檔案的時候可以考慮設定路徑為這個。
內部路徑，getFilesDir()，getCacheDir()
外部儲存，通常是不可用的，因為使用者會手動移除或者懸掛，所有在訪問之前要判斷外部儲存的狀態。
<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> 使用外部儲存空間，需要新增許可權，<manifest ...> <uses-permission
android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> ...
</manifest>
4.SQLiteOpenHelper資料庫儲存;步驟如下，
<span style="font-size:18px;">a.自定義類繼承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>下面的增刪查改都需要在子執行緒中進行;
<span style="font-size:18px;">b.寫入資料，
// Gets the data repository in write mode
SQLiteDatabase db = mDbHelper.getWritableDatabase();
// Create a new map of values, where column names are the keys
ContentValues 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 row
long newRowId;
newRowId = db.insert(
FeedEntry.TABLE_NAME,
FeedEntry.COLUMN_NAME_NULLABLE,
values);
c.讀出資料，
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 Cursor
String 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.刪除資料，
// 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.更新資料，
SQLiteDatabase db = mDbHelper.getReadableDatabase();
// New value for one column
ContentValues values = new ContentValues();
values.put(FeedEntry.COLUMN_NAME_TITLE, title);
// Which row to update, based on the ID
String selection = FeedEntry.COLUMN_NAME_ENTRY_ID + " LIKE ?";
String[] selectionArgs = { String.valueOf(rowId) };
int count = db.update(
FeedReaderDbHelper.FeedEntry.TABLE_NAME,
values,
selection,
selectionArgs);</span>