实现跨程序数据共享
public class DatabaseProvider extends ContentProvider {
public static final int BOOK_DIR = 0;
public static final int BOOK_ITEM = 1;
public static final int CATEGORY_DIR = 2;
public static final int CATEGORY_ITEM = 3;
public static final String AUTHORITY = "com.example.databasetest.provider";
private static UriMatcher uriMatcher;
private MyDatabaseHelper dbHelper;
static {
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI(AUTHORITY, "book", BOOK_DIR);
uriMatcher.addURI(AUTHORITY, "book/#", BOOK_ITEM);
uriMatcher.addURI(AUTHORITY, "category", CATEGORY_DIR);
uriMatcher.addURI(AUTHORITY, "category/#", CATEGORY_ITEM);
}
@Override
public boolean onCreate() {
dbHelper = new MyDatabaseHelper(getContext(), "BookStore.db", null, 2);
return true;
}
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
// 查询数据
SQLiteDatabase db = dbHelper.getReadableDatabase();
Cursor cursor = null;
switch (uriMatcher.match(uri)) {
case BOOK_DIR:
cursor = db.query("Book", projection, selection, selectionArgs, null, null, sortOrder);
break;
case BOOK_ITEM:
String bookId = uri.getPathSegments().get(1);
cursor = db.query("Book", projection, "id = ?", new String[] { bookId }, null, null, sortOrder);
break;
case CATEGORY_DIR:
cursor = db.query("Category", projection, selection, selectionArgs, null, null, sortOrder);
break;
case CATEGORY_ITEM:
String categoryId = uri.getPathSegments().get(1);
cursor = db.query("Category", projection, "id = ?", new String[] { categoryId }, null, null, sortOrder);
break;
default:
break;
}
return cursor;
}
@Override
public Uri insert(Uri uri, ContentValues values) {
// 添加数据
SQLiteDatabase db = dbHelper.getWritableDatabase();
Uri uriReturn = null;
switch (uriMatcher.match(uri)) {
case BOOK_DIR:
case BOOK_ITEM:
long newBookId = db.insert("Book", null, values);
uriReturn = Uri.parse("content://" + AUTHORITY + "/book/" + newBookId);
break;
case CATEGORY_DIR:
case CATEGORY_ITEM:
long newCategoryId = db.insert("Category", null, values);
uriReturn = Uri.parse("content://" + AUTHORITY + "/category/" + newCategoryId);
break;
default:
break;
}
return uriReturn;
}
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
// 更新数据
SQLiteDatabase db = dbHelper.getWritableDatabase();
int updatedRows = 0;
switch (uriMatcher.match(uri)) {
case BOOK_DIR:
updatedRows = db.update("Book", values, selection, selectionArgs);
break;
case BOOK_ITEM:
String bookId = uri.getPathSegments().get(1);
updatedRows = db.update("Book", values, "id = ?", new String[] { bookId });
break;
case CATEGORY_DIR:
updatedRows = db.update("Category", values, selection, selectionArgs);
break;
case CATEGORY_ITEM:
String categoryId = uri.getPathSegments().get(1);
updatedRows = db.update("Category", values, "id = ?", new String[] { categoryId });
break;
default:
break;
}
return updatedRows;
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
// 删除数据
SQLiteDatabase db = dbHelper.getWritableDatabase();
int deletedRows = 0;
switch (uriMatcher.match(uri)) {
case BOOK_DIR:
deletedRows = db.delete("Book", selection, selectionArgs);
break;
case BOOK_ITEM:
String bookId = uri.getPathSegments().get(1);
deletedRows = db.delete("Book", "id = ?", new String[] { bookId });
break;
case CATEGORY_DIR:
deletedRows = db.delete("Category", selection, selectionArgs);
break;
case CATEGORY_ITEM:
String categoryId = uri.getPathSegments().get(1);
deletedRows = db.delete("Category", "id = ?", new String[] { categoryId });
break;
default:
break;
}
return deletedRows;
}
@Override
public String getType(Uri uri) {
switch (uriMatcher.match(uri)) {
case BOOK_DIR:
return "vnd.android.cursor.dir/vnd.com.example.databasetest. provider.book";
case BOOK_ITEM:
return "vnd.android.cursor.item/vnd.com.example.databasetest. provider.book";
case CATEGORY_DIR:
return "vnd.android.cursor.dir/vnd.com.example.databasetest. provider.category";
case CATEGORY_ITEM:
return "vnd.android.cursor.item/vnd.com.example.databasetest. provider.category";
}
return null;
}
}
首先在类的一开始，同样是定义了四个常量，分别用于表示访问Book表中的所有数据、访问Book表中的单条数据、访问Category表中的所有数据和访问Category表中的单条数据。然后在静态代码块里对UriMatcher进行了初始化操作，将期望匹配的几种URI格式添加了进去。
onCreate()方法创建了一个MyDatabaseHelper的实例，然后返回true表示内容提供器初始化成功，这时数据库就已经完成了创建或升级操作。
query()方法，在这个方法中先获取到了SQLiteDatabase的实例，然后根据传入的Uri参数判断出用户想要访问哪张表，再调用SQLiteDatabase的query()进行查询，并将Cursor对象返回就好了。注意当访问单条数据的时候有一个细节，这里调用了Uri对象的getPathSegments()方法，它会将内容URI权限之后的部分以“/”符号进行分割，并把分割后的结果放入到一个字符串列表中，那这个列表的第0个位置存放的就是路径，第1个位置存放的就是id了。得到了id之后，再通过selection和selectionArgs参数进行约束，就实现了查询单条数据的功能。
insert()方法，先获取到了SQLiteDatabase的实例，然后根据传入的Uri参数判断出用户想要往哪张表里添加数据，再调用SQLiteDatabase的insert()方法进行添加就可以了。注意insert()方法要求返回一个能够表示这条新增数据的URI，所以我们还需要调用Uri.parse()方法来将一个内容URI解析成Uri对象，当然这个内容URI是以新增数据的id结尾的。
update()方法了，先获取SQLiteDatabase的实例，然后根据传入的Uri参数判断出用户想要更新哪张表里的数据，再调用SQLiteDatabase的update()方法进行更新就好了，受影响的行数将作为返回值返回。
delete()方法，先获取到SQLiteDatabase的实例，然后根据传入的Uri参数判断出用户想要删除哪张表里的数据，再调用SQLiteDatabase的delete()方法进行删除就好了，被删除的行数将作为返回值返回。
将内容提供器在AndroidManifest.xml文件中注册。
<provider
android:name="com.example.databasetest.DatabaseProvider"
android:authorities="com.example.databasetest.provider"
Android:exported="true">
</provider>
访问程序共享的数据
添加数据
Uri uri = Uri.parse("content://com.example.databasetest.provider/book");
ContentValues values = new ContentValues();
values.put("name", "A Clash of Kings");
values.put("author", "George Martin");
values.put("pages", 1040);
values.put("price", 22.85);
Uri newUri = getContentResolver().insert(uri, values);
newId = newUri.getPathSegments().get(1);
查询数据
Uri uri = Uri.parse("content://com.example.databasetest.provider/book");
Cursor cursor = getContentResolver().query(uri, null, null,null, null);
if(cursor!=null) {
while (cursor.moveToNext()) {
String name = cursor.getString(cursor.getColumnIndex("name"));
String author = cursor.getString(cursor.getColumnIndex("author"));
int pages = cursor.getInt(cursor.getColumnIndex("pages"));
double price = cursor.getDouble(cursor.getColumnIndex("price"));
}
}
更新数据
Uri uri = Uri.parse("content://com.example.databasetest. provider/book/" + newId);
ContentValues values = new ContentValues();
values.put("name", "A Storm of Swords");
values.put("pages", 1216);
values.put("price", 24.05);
getContentResolver().update(uri, values, null, null);
删除数据
Uri uri = Uri.parse("content://com.example.databasetest. provider/book/" + newId);
getContentResolver().delete(uri, null, null);
