概述
Android提供专门用于不同应用间进行数据共享的方式，底层实现是Binder，但是使用的过程比AIDL简单许多。主要用于第三方应用访问本应用的数据库中的数据。Contentprovider中有六个方法，分别是
- query,update,insert,delete.（CRUD）就不多说了
- getType:用来返回一个Uri请求所对应的的MIME类型（媒体型），比如图片，视频等
- oncreate:表示ContentProvider的创建，一般用来初始化一些参数
下面进行简单的演示
1、首先创建一个BooksProvider类继承ContentProvider，重写上面所说的6个方法
BooksProvider extends ContentProvider {
public static final String TAG = "BooksProviders";
@Override
public boolean onCreate() {
Log.d(TAG,"onCerate,current thread:"+Thread.currentThread().getName());
return true;
}
@Nullable
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
Log.d(TAG,"query,current thread:"+Thread.currentThread().getName());
return null;
}
@Nullable
@Override
public String getType(Uri uri) {
Log.d(TAG,"getType,current thread:"+Thread.currentThread().getName());
return null;
}
@Nullable
@Override
public Uri insert(Uri uri, ContentValues values) {
Log.d(TAG,"insert,current thread:"+Thread.currentThread().getName());
return null;
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
Log.d(TAG,"delete,current thread:"+Thread.currentThread().getName());
return null;
}
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
Log.d(TAG,"update,current thread:"+Thread.currentThread().getName());
return 0;
}
}
2、我们需要在主菜单中注册这个BooksProvider，其中android:authorities是Contenprovider的唯一标识，通过这个属性，外部应用可以访问到我们的BookProvider，还可以给他添加权限，这样外部应用访问时，也必须要申请此权限才能访问（android：premisson）
3、接下来我们通过ContentResolver对象的query（）方法去查询BookProvider中的数据，其中我们的com.example.ticker.bookprovider.BooksProvider就是唯一的标识
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Uri uri = Uri.parse("content://com.example.ticker.bookprovider.BooksProvider");
getContentResolver().query(uri,null,null,null,null);
}
}
运行下应用，我们可以在日记窗口看到如下信息
到这里，ContentProvider就已经基本完成了。接下来演示外部应用通过BookProvider访问本应用的图书信息。为了更好演示效果
1、先创建一个简单的数据库，代码如下
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_VWESION = 1;
private String CREATE_BOOK_TABLE = "CREATE TABLE IF NOT EXISTS "+ BOOK_TABLE_NAME + "(id integer primary key autoincrement,name varchar(30))";
private String CREATE_USER_TABLE = "CREATE TABLE IF NOT EXISTS "+USER_TABLE_NAME+"(id integer primary key autoincrement,name varchar(30),sex integer)";
public DbOpenHelper(Context context) {
super(context, DB_NAME, null, DB_VWESION);
}
@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) {
}
}
2、contentprovider通过URI来区分外界要访问的数据集合，为了知道外界访问的是哪个表，我们需要单独的URI和RUI_CODE并将Uri和对应的URI_CODE相关联。这样外界在请求的时候，我们就能知道访问的是哪个表
public class BookProvider extends ContentProvider {
public static final String TAG = "BooksProviders";
public static final String AUTHORITY = "com.example.ticker.bookprovider.BooksProvider";
public static final Uri BOOK_CONTENT_URI = Uri.parse("content://"+AUTHORITY+"/book");
public static final Uri USER_CONTENT_URI = Uri.parse("content://"+AUTHORITY+"/user");
public static final int BOOK_URI_CODE = 0;
public static final int USER_URI_CODE =1;
private static final UriMatcher sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
static{
sUriMatcher.addURI(AUTHORITY,"book",BOOK_URI_CODE);
sUriMatcher.addURI(AUTHORITY,"user",USER_URI_CODE);
}
.......
}
我们分别为book表和user表指定了Uri.
book对应“content://com.example.ticker.bookprovider.BooksProvider/book”
user对应“content://com.example.ticker.bookprovider.BooksProvider/user”
通过sUriMatcher.addURI（）方法将其关联起来
3、将Uri和Uri_Code管理后，我们可以通过如下方式获取外界所要访问的数据源，根据Uri先取出Uri_Code，再根据Uri_Code获取数据表的名称
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;
}
4、接下来就可以实现CURD方法了，首先从Uri中取出外界要访问的表的名称，然后根据外界传递的查询参数进行数据库查询操作
@Nullable
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
Log.d(TAG,"query,current thread:"+Thread.currentThread().getName());
String table = getTableName(uri);
if (table==null)
{
throw new IllegalArgumentException("Unsupported URI:"+uri);
}
return mDb.query(table,projection,selection,selectionArgs,null,null,sortOrder,null);
}
另外需要注意，update、insert和delete方法会引起数据源的改变，所以需要通过ContentResolver的notifyChange（）方法来通知外界ContentProvider中数据发生了改变。要观察一个ContentProvider中的数据改变情况，可以通过ContentResolver的registerContentOberver方法来注册观察这，通过unregisterContentObserver方法来解除观。
下面是BookProvider完整代码
public class
BooksProvider extends ContentProvider {
public static final String TAG = "BooksProviders";
public static final String AUTHORITY = "com.example.ticker.bookprovider.BooksProvider";
public static final Uri BOOK_CONTENT_URI = Uri.parse("content://"+AUTHORITY +"/book");
public static final Uri USER_CONTENT_URI = Uri.parse("content://"+AUTHORITY +"/user");
public static final int BOOK_URI_CODE = 0;
public static final int USER_URI_CODE = 1;
private static final UriMatcher sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
private SQLiteDatabase mDb;
private Context mContext;
static{
sUriMatcher.addURI(AUTHORITY,"book",BOOK_URI_CODE);
sUriMatcher.addURI(AUTHORITY,"user",USER_URI_CODE);
}
@Override
public boolean onCreate() {
Log.d(TAG,"onCerate,current thread:"+Thread.currentThread().getName());
mContext = getContext();
initProviderData();
return true;
}
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,'jake ',1);");
mDb.execSQL("insert into user values(2,'jasmine ',0);");
}
@Nullable
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
Log.d(TAG,"query,current thread:"+Thread.currentThread().getName());
String table = getTableName(uri);
if (table==null)
{
throw new IllegalArgumentException("Unsupported URI:"+uri);
}
return mDb.query(table,projection,selection,selectionArgs,null,null,sortOrder,null);
}
@Nullable
@Override
public String getType(Uri uri) {
Log.d(TAG,"getType,current thread:"+Thread.currentThread().getName());
return null;
}
@Nullable
@Override
public Uri insert(Uri uri, ContentValues values) {
Log.d(TAG,"insert,current thread:"+Thread.currentThread().getName());
String table = getTableName(uri);
if (table==null){
throw new IllegalArgumentException("Unsupport URI");
}
mDb.insert(table,null,values);
mContext.getContentResolver().notifyChange(uri,null);
return uri;
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
Log.d(TAG,"delete,current thread:"+Thread.currentThread().getName());
String table = getTableName(uri);
if (table==null){
throw new IllegalArgumentException("Unsupport URI");
}
int count = mDb.delete(table,selection,selectionArgs);
if (count>0){
getContext().getContentResolver().notifyChange(uri,null);
}
return count;
}
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
Log.d(TAG,"update,current thread:"+Thread.currentThread().getName());
String table = getTableName(uri);
if (table==null){
throw new IllegalArgumentException("Unsupport URI");
}
int row = mDb.update(table,values,selection,selectionArgs);
if (row>0){
getContext().getContentResolver().notifyChange(uri,null);
}
return row;
}
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;
}
}
5、最后我们通过外部访问，看是否能出现我们预期的效果
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void onclick(View view){
Uri uri = Uri.parse("content://com.example.ticker.bookprovider.BooksProvider/book");
ContentValues values = new ContentValues();
values.put("id",6);
values.put("name","程序设计艺术");
getContentResolver().insert(uri,values);
Cursor bookCursor = getContentResolver().query(uri,new String[]{"id","name"},null,null,null);
while(bookCursor.moveToNext()){
Books book = new Books();
book.setId(bookCursor.getInt(0));
book.setName(bookCursor.getString(1));
Log.d(BooksProvider.TAG,"query book id:"+book.getId()+" book name:" + book.getName());
}
bookCursor.close();
Uri userUri = Uri.parse("content://com.example.ticker.bookprovider.BooksProvider//user");
Cursor userCursor = getContentResolver().query(userUri,new String[]{"id","name","sex"},null,null,null);
while(userCursor.moveToNext()){
User user = new User();
user.setId(userCursor.getInt(0));
user.setName(userCursor.getString(1));
user.setSex(userCursor.getInt(2));
Log.d(BooksProvider.TAG,"query user id:"+user.getId()+" name:"+user.getName()+" sex:"+user.getSex());
}
userCursor.close();
}
}
效果下图
案例地址：
ContentProvider简单实例
学习资料
Android开发艺术探索