Create your own content provider by creating a new class that inherits ContentProvider.
There are six abstract methods in the ContentProvider class. When we use subclasses to inherit it, we need to rewrite all six methods.
- New MyProvider inherits from ContentProvider. Write several methods.
public class MyProvider extends ContentProvider {
@Override
public boolean onCreate() {
return false;
}
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
return null;
}
@Override
public Uri insert(Uri uri, ContentValues values) {
return null;
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
return 0;
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
return 0;
}
@Override
public String getType(Uri uri) {
return null;
}
}1. onCreate()
When the content provider is initialized, it is usually called here to complete the creation and upgrade of the database.
Returning true indicates successful initialization of the content provider, and returning false indicates failure.
Note that the content provider is initialized only if there is a ContentResolver that tries to access the data in our program.
2. query()
Query data from the content provider.
The uri parameter is used to determine which table to query, the project parameter to determine which columns to query, the selection and selectionArgs parameters to constrain which rows to query, and the sortOrder parameter to sort the results.
The results of the query are stored in the Cursor object and returned.
3. insert()
Add a data to the content provider.
The uri parameter is used to determine the table to be added, and the data to be added is stored in the values parameter.
When the addition is complete, a URI is returned to represent the new record.
4. update()
Update existing data in the content provider.
The uri parameter is used to determine which table data is updated, the new data is stored in the values parameter, and the selection and selectionArgs parameters are used to constrain which rows are updated.
The number of rows affected will be returned as a return value.
5. delete()
Delete data from the content provider.
The uri parameter is used to determine which table data is deleted, and the selection and selectionArgs parameters are used to constrain which rows are deleted.
The number of deleted rows will be returned as a return value.
6. getType()
Returns the corresponding MIME type based on the incoming content URI.
The MIME string corresponding to a content URI consists of three parts:
It must start with vnd.
If the content URI ends in a path, then android.cursor.dir /, and if the content URI ends in id, then android.cursor.item /.
Finally, connect vnd.
For content://com.example.app.provider/table1, the corresponding MIME type is:
vnd.android.cursor.dir/vnd.com.example.app.provider.table1
For content://com.example.app.provider/table1/1, the corresponding MIME type is:
vnd.android.cursor.item/vnd.com.example.app.provider.table1
Implement getType() logic:
public class MyProvider extends ContentProvider {
......
@Override
public String getType(Uri uri) {
switch (uriMatcher.match(uri)) {
case TABLE1_DIR:
return "vnd.android.cursor.dir/vnd.com.example.app.provider.table1";
case TABLE1_ITEM:
return "vnd.android.cursor.item/vnd.com.example.app.provider.table1";
case TABLE2_DIR:
return "vnd.android.cursor.dir/vnd.com.example.app.provider.table2";
case TABLE2_ITEM:
return "vnd.android.cursor.item/vnd.com.example.app.provider.table2";
default:
break;
}
return null;
}
}- By matching the content URI with UriMatcher, we can know which data in which table the incoming Uri object wants to access.
The content URI of any table can be matched:
content://com.example.app.provider/*
Content URI s that match any row of data in table1 table:
content://com.example.app.provider/table1/#
An addURI() method is provided in UriMatcher, which receives three parameters to pass in permissions, paths, and a custom code, respectively.
When UriMatcher's match() method is called, a Uri object can be passed in and back.
The return value is a custom code that matches the corresponding Uri object.
With this code, we can determine which table or row the caller expects to access.
public static final int TABLE1_DIR = 0;
public static final int TABLE1_ITEM = 1;
public static final int TABLE2_DIR = 2;
public static final int TABLE2_ITEM = 3;
private static UriMatcher uriMatcher;
static {
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI("com.example.app.provider", "table1", TABLE1_DIR);
uriMatcher.addURI("com.example.app.provider ", "table1/#", TABLE1_ITEM);
uriMatcher.addURI("com.example.app.provider ", "table2", TABLE2_ITEM);
uriMatcher.addURI("com.example.app.provider ", "table2/#", TABLE2_ITEM);
}- In several methods of MyProvider, we use switch to judge uriMatcher.match(uri), and locate the purpose to the corresponding table or row according to the purpose of different Uri.
public class MyProvider extends ContentProvider {
public static final int TABLE1_DIR = 0;
public static final int TABLE1_ITEM = 1;
public static final int TABLE2_DIR = 2;
public static final int TABLE2_ITEM = 3;
private static UriMatcher uriMatcher;
static {
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI("com.example.app.provider", "table1", TABLE1_DIR);
uriMatcher.addURI("com.example.app.provider ", "table1/#", TABLE1_ITEM);
uriMatcher.addURI("com.example.app.provider ", "table2", TABLE2_ITEM);
uriMatcher.addURI("com.example.app.provider ", "table2/#", TABLE2_ITEM);
}
......
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
switch (uriMatcher.match(uri)) {
case TABLE1_DIR:
// Query all data in table1 table
break;
case TABLE1_ITEM:
// Query single data in table1 table
break;
case TABLE2_DIR:
// Query all data in table2 table
break;
case TABLE2_ITEM:
// Query single data in table2 table
break;
default:
break;
}
......
}
......
}- After defining the purpose, it depends on the operation of SQLiteDatabase to complete the addition, deletion and modification check.
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) {
// Query data
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) {
// Add data
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) {
// Update data
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) {
// Delete data
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;
}
}getPathSegments() method
It divides the part after the content URI permission into "/" symbols and puts the result into a list of strings, where the path is stored in the tenth place and the id is stored in the first place.
- To register in Android Manifest. xml.
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.databasetest"
android:versionCode="1"
android:versionName="1.0" >
......
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
......
<provider
android:name="com.example.databasetest.DatabaseProvider"
android:authorities="com.example.databasetest.provider" >
</provider>
</application>
</manifest>