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ContentProvider主要應用于進程間數(shù)據(jù)共享. 對于應用而言, 多進程并不會經常使用, 因而較少使用ContentProvider, 是最不常見的四大組件(Activity, Service, BroadcastReceiver, ContentProvider). 但是其優(yōu)異的性能與便捷, 對于多應用共享數(shù)據(jù)而言, 非常重要, 比如共享同一份計步數(shù)據(jù)等. 開發(fā)者只有掌握多種技能, 才能在開發(fā)中游刃有余, 用最優(yōu)的方式完成項目, 提升應用性能, 間接提高用戶體驗. 本文借用Demo, 講解ContentProvider共享數(shù)據(jù)的要點.
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SQLite
ContentProvider需要媒介進行數(shù)據(jù)存儲, 最常用的就是SQLite數(shù)據(jù)庫.
SQLite數(shù)據(jù)庫繼承SQLiteOpenHelper類, 提供數(shù)據(jù)庫名稱, 表名, 版本. 在onCreate方法中, 創(chuàng)建數(shù)據(jù)庫表, 添加字段.
本示例使用兩張表, 書籍和用戶.
public class DbOpenHelper extends SQLiteOpenHelper {
private static final String DB_NAME = "book_provider.db";
public static final String BOOK_TABLE_NAME = "book";
public static final String USER_TABLE_NAME = "user";
private static final int DB_VERSION = 1;
private String CREATE_BOOK_TABLE = "CREATE TABLE IF NOT EXISTS "
+ BOOK_TABLE_NAME + "(_id INTEGER PRIMARY KEY, name TEXT)";
private String CREATE_USER_TABLE = "CREATE TABLE IF NOT EXISTS "
+ USER_TABLE_NAME + "(_id INTEGER PRIMARY KEY, name TEXT, sex INT)";
public DbOpenHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
}
@Override public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_BOOK_TABLE);
db.execSQL(CREATE_USER_TABLE);
}
@Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
直接使用數(shù)據(jù)庫的情況較少, 也比較復雜, 推薦使用一些經典ORM數(shù)據(jù)庫, 如Sugar等, 簡化管理. ORM, 即對象關系映射.
ContentProvider
ContentProvider提供數(shù)據(jù)訪問的接口, CRUD增刪改查. 在onCreate中, 初始化數(shù)據(jù)庫, 并添加數(shù)據(jù).
@Override public boolean onCreate() {
showLogs("onCreate 當前線程: " + Thread.currentThread().getName());
mContext = getContext();
initProviderData(); // 初始化Provider數(shù)據(jù)
return false;
}
private void initProviderData() {
mDb = new DbOpenHelper(mContext).getWritableDatabase();
mDb.execSQL("delete from " + DbOpenHelper.BOOK_TABLE_NAME);
mDb.execSQL("delete from " + DbOpenHelper.USER_TABLE_NAME);
mDb.execSQL("insert into book values(3,'Android');");
mDb.execSQL("insert into book values(4, 'iOS');");
mDb.execSQL("insert into book values(5, 'HTML5');");
mDb.execSQL("insert into user values(1, 'Spike', 1);");
mDb.execSQL("insert into user values(2, 'Wang', 0);");
}
CRUD的參數(shù)是Uri, 數(shù)據(jù)庫需要使用表名, 為了便于從Uri映射到表名, 使用關系轉換.
private String getTableName(Uri uri) {
String tableName = null;
switch (sUriMatcher.match(uri)) {
case BOOK_URI_CODE:
tableName = DbOpenHelper.BOOK_TABLE_NAME;
break;
case USER_URI_CODE:
tableName = DbOpenHelper.USER_TABLE_NAME;
break;
default:
break;
}
return tableName;
}
添加數(shù)據(jù)insert, 可以注冊內容改變的監(jiān)聽, 插入數(shù)據(jù)時, 廣播更新, 即notifyChange.
@Nullable @Override public Uri insert(Uri uri, ContentValues values) {
showLogs("insert");
String table = getTableName(uri);
if (TextUtils.isEmpty(table)) {
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
mDb.insert(table, null, values);
// 插入數(shù)據(jù)后通知改變
mContext.getContentResolver().notifyChange(uri, null);
return null;
}
刪除數(shù)據(jù)delete, 返回刪除數(shù)據(jù)的數(shù)量, 大于0即刪除成功.
@Override public int delete(Uri uri, String selection, String[] selectionArgs) {
showLogs("delete");
String table = getTableName(uri);
if (TextUtils.isEmpty(table)) {
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
int count = mDb.delete(table, selection, selectionArgs);
if (count > 0) {
mContext.getContentResolver().notifyChange(uri, null);
}
return count; // 返回刪除的函數(shù)
}
修改數(shù)據(jù)update, 與刪除類似, 返回修改數(shù)據(jù)的數(shù)量.
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
showLogs("update");
String table = getTableName(uri);
if (TextUtils.isEmpty(table)) {
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
int row = mDb.update(table, values, selection, selectionArgs);
if (row > 0) {
mContext.getContentResolver().notifyChange(uri, null);
}
return row; // 返回更新的行數(shù)
}
查詢數(shù)據(jù)query, 返回數(shù)據(jù)庫的游標, 處理數(shù)據(jù).
@Nullable @Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
showLogs("query 當前線程: " + Thread.currentThread().getName());
String tableName = getTableName(uri);
if (TextUtils.isEmpty(tableName)) {
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
return mDb.query(tableName, projection, selection, selectionArgs, null, null, sortOrder, null);
}
注意Uri和表名的轉換可能為空, 使用
TextUtils.isEmpty判空.
共享數(shù)據(jù)
使用ContentProvider的獨立進程, 模擬進程間共享數(shù)據(jù).
<provider
android:name=".BookProvider"
android:authorities="org.wangchenlong.book.provider"
android:permission="org.wangchenlong.BOOK_PROVIDER"
android:process=":provider"/>
在AndroidManifest中, 把Provider注冊在
:provider進程中, 與主進程分離.
添加數(shù)據(jù), 通過Uri找到ContentProvider, 使用ContentResolver的insert方法, 添加ContentValues數(shù)據(jù).
public void addBooks(View view) {
Uri bookUri = BookProvider.BOOK_CONTENT_URI;
ContentValues values = new ContentValues();
values.put("_id", 6);
values.put("name", "信仰上帝");
getContentResolver().insert(bookUri, values);
}
查詢數(shù)據(jù)query, 與數(shù)據(jù)庫的使用方式類似, 解析出Cursor, 通過移動Cursor, 找到所有匹配的結果.
public void showBooks(View view) {
String content = "";
Uri bookUri = BookProvider.BOOK_CONTENT_URI;
Cursor bookCursor = getContentResolver().query(bookUri, new String[]{"_id", "name"}, null, null, null);
if (bookCursor != null) {
while (bookCursor.moveToNext()) {
Book book = new Book();
book.bookId = bookCursor.getInt(0);
book.bookName = bookCursor.getString(1);
content += book.toString() + "\n";
Log.e(TAG, "query book: " + book.toString());
mTvShowBooks.setText(content);
}
bookCursor.close();
}
}
效果
ContentProvider封裝了跨進程共享的邏輯, 我們只需要Uri即可訪問數(shù)據(jù), 使用共享數(shù)據(jù)非常便捷, 需要掌握簡單的使用方式.
OK, that's all! Enjoy it!
