ContentProvider作用
为存储和获取数据提供了统一的接口
实现了不用应用间的数据共享
Android为常用数据（如声音、图片、视频和通讯录等）提供的默认的ContentProvider支持
相关概念介绍
ContentProvider简介
为了实现向其他应用共享数据，需要继承一个抽象类ContentProvider，并实现如下几个抽象方法。
public class MyProvider extends ContentProvider {
@Override
public boolean onCreate() {
return false;
}
@Nullable
@Override
public Cursor
query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
return null;
}
@Nullable
@Override
public String
getType(Uri uri) {
return null;
}
@Nullable
@Override
public Uri
insert(Uri uri, ContentValues values) {
return null;
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
return 0;
}
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
return 0;
}
}
看到这些抽象方法的参数是不是和数据库的相关操作很像。因此一般情况下，我们都是用数据库来存储数据。
Uri简介
概念：通用资源标示符（Uniform Resource Identifier）
组成部分：
scheme 访问资源的命名机制
authority 存放资源的主机名
path 资源自身的名称
格式：scheme://authority/path，其中authority还包括host的port。例如：
content://com.cydia.test:200/login/username
content为schemecom.cydia.test:200为authority（com.cydia.test为host，200为port）login/username为path。
Sqlite简介
参考文章《Android中的数据库应用小结》
本应用内的provider构建
众所周知，ContentProvider是用来向其他应用共享本应用内的数据，因此，我们首先需要确定数据在本应用内的存储方式。而考虑到继承ContentProvider需要实现的抽象方法（与sqlite的操作方法太相似），我们使用sqlite来存储数据。
创建数据库: MySqliteHelper
public class MySqliteHelper extends SQLiteOpenHelper {
public static final String DB_NAME =
"cydia.db";
public static final int DB_VERSION =
3;
public static final String TABLE_NAME =
"bookstore";
public static final String COLUMN_ID =
"id";
public static final String COLUMN_NAME =
"name";
public static final String COLUMN_AUTHOR =
"author";
public static final String COLUMN_PRICE =
"price";
public static final String COLUMN_PAGES =
"pages";
public static final String CREATE_TABLE =
"CREATE TABLE IF NOT EXISTS " + TABLE_NAME +
" (" +
COLUMN_ID +
" integer primary key autoincrement," +
COLUMN_NAME +
" text NOT NULL," +
COLUMN_AUTHOR +
" text," +
COLUMN_PRICE +
" real," +
COLUMN_PAGES +
" integer)";
public MySqliteHelper(Context context) {
super(context, DB_NAME,
null, DB_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db,
int oldVersion,
int newVersion) {
db.execSQL(
"DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
}
创建数据管理类: DBManager
public class DBManager {
private volatile static DBManager sInstance;
private SQLiteDatabase db;
private DBManager(Context context) {
MySqliteHelper helper =
new MySqliteHelper(context);
db = helper.getWritableDatabase();
}
public static DBManager
getInstance(Context context) {
if (sInstance ==
null) {
synchronized (DBManager.class) {
if (sInstance ==
null) {
sInstance =
new DBManager(context);
}
}
}
return sInstance;
}
public long add(ContentValues contentValues) {
return db.insert(MySqliteHelper.TABLE_NAME,
null, contentValues);
}
public int delete(String whereClause, String[] whereArgs) {
return db.delete(MySqliteHelper.TABLE_NAME, whereClause, whereArgs);
}
public int update(ContentValues contentValues, String whereClause, String[] whereArgs) {
return db.update(MySqliteHelper.TABLE_NAME, contentValues, whereClause, whereArgs);
}
public Cursor
query(String[] columns, String selection,
String[] selectionArgs, String groupBy, String having,
String orderBy) {
return db.query(MySqliteHelper.TABLE_NAME, columns, selection,
selectionArgs, groupBy, having,
orderBy);
}
public void closeDB() {
db.close();
}
}
继承ContentProvider类
public class MyProvider extends ContentProvider {
private Context context;
private ContentResolver contentResolver;
private static final String AUTHORITY =
"com.pptv.test";
private static final int ALL_BOOKS =
1;
private static final int SINGLE_BOOK =
1;
private static UriMatcher uriMatcher =
new UriMatcher(UriMatcher.NO_MATCH);
static {
uriMatcher.addURI(AUTHORITY, MySqliteHelper.TABLE_NAME, ALL_BOOKS);
uriMatcher.addURI(AUTHORITY, MySqliteHelper.TABLE_NAME +
"/#", SINGLE_BOOK);
}
@Override
public boolean onCreate() {
context = getContext();
contentResolver = context.getContentResolver();
return true;
}
@Nullable
@Override
public String
getType(Uri uri) {
if (uriMatcher.match(uri) == ALL_BOOKS) {
return "vnd.android.cursor.dir/" + MySqliteHelper.TABLE_NAME;
}
else if(uriMatcher.match(uri) == SINGLE_BOOK) {
return "vnd.android.cursor.item/" + MySqliteHelper.TABLE_NAME;
}
return null;
}
@Nullable
@Override
public Uri
insert(Uri uri, ContentValues values) {
Uri ret =
null;
if (uriMatcher.match(uri) == ALL_BOOKS) {
long id = DBManager.getInstance(context).add(values);
ret = ContentUris.withAppendedId(uri, id);
contentResolver.notifyChange(ret,
null);
}
return ret;
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
int id =
0;
if (uriMatcher.match(uri) == ALL_BOOKS) {
id = DBManager.getInstance(context).delete(selection, selectionArgs);
contentResolver.notifyChange(uri,
null);
}
else if(uriMatcher.match(uri) == SINGLE_BOOK) {
long deleted_id = ContentUris.parseId(uri);
id = DBManager.getInstance(context).delete(MySqliteHelper.COLUMN_ID +
"=?",
new String[]{deleted_id +
""});
contentResolver.notifyChange(uri,
null);
}
return id;
}
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
int id =
0;
if (uriMatcher.match(uri) == ALL_BOOKS) {
id = DBManager.getInstance(context).update(values, selection, selectionArgs);
contentResolver.notifyChange(uri,
null);
}
else if(uriMatcher.match(uri) == SINGLE_BOOK) {
long update_id = ContentUris.parseId(uri);
id = DBManager.getInstance(context).update(values, MySqliteHelper.COLUMN_ID +
"=?",
new String[]{update_id +
""});
contentResolver.notifyChange(uri,
null);
}
return id;
}
@Nullable
@Override
public Cursor
query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
Cursor cursor =
null;
if (uriMatcher.match(uri) == ALL_BOOKS) {
cursor = DBManager.getInstance(context).query(projection, selection, selectionArgs,
null,
null, sortOrder);
cursor.setNotificationUri(contentResolver, uri);
}
else if(uriMatcher.match(uri) == SINGLE_BOOK) {
long select_id = ContentUris.parseId(uri);
cursor = DBManager.getInstance(context).query(projection, MySqliteHelper.COLUMN_ID +
"=?",
new String[]{select_id +
""},
null,
null, sortOrder);
cursor.setNotificationUri(contentResolver, uri);
}
return cursor;
}
}
UriMatcher的作用在于，控制不同Uri的操作权限以及操作内容。 比如上述code所示：content://com.pptv.test/bookstore 执行查找其返回所有符合条件的记录，而content://com.pptv.test/bookstore/4 执行查找方法，其仅仅返回id为4的记录
在AndroidManifest中注册provider
<provider
android:name=
".provider.MyProvider"
android:authorities=
"com.pptv.test"
android:enabled=
"true"
android:exported=
"true" />
android:authorities 访问这个provider的权限，需要和MyProvider中定义的AUTHORITY保持一致。android:enabled 指定这个内容提供器是否能够被系统安装android:exported 指定该内容提供器是否能够被其他的应用程序组件使用
其他应用使用Provider来访问数据
获取一个ContentResolver类
直接使用Content类的getContentResolver()方法就能获取到。
通过ContentResolver执行增删改查操作
ContentResolver的主要方法：
返回值函数声明
final Uriinsert(Uri url, ContentValues values)final intdelete(Uri url, String where, String[] selectionArgs)final intupdate(Uri uri, ContentValues values, String where, String[] selectionArgs)final Cursorquery(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder)
例如：查询所有的数据
private String
getData(){
StringBuilder sb =
new StringBuilder();
ContentResolver cr =
this.getContentResolver();
Uri uri = Uri.parse(
"content://com.pptv.test/bookstore");
Cursor cursor = cr.query(uri,
null,
null,
null,
null);
if(cursor !=
null){
Log.i(TAG,
"cursor != null");
while(cursor.moveToNext()){
String name = cursor.getString(cursor.getColumnIndex(
"name"));
String author = cursor.getString(cursor.getColumnIndex(
"author"));
float price = cursor.getFloat(cursor.getColumnIndex(
"price"));
int pages = cursor.getInt(cursor.getColumnIndex(
"pages"));
sb.append(
"name = " + name +
", ")
.append(
"author = " + author +
", ")
.append(
"price = " + price +
" ,")
.append(
"pages = " + pages +
"\n");
}
cursor.close();
}
return sb.toString();
}
