Android中ContentProvider和ContentResolver详解

Android中ContentProvider和ContentResolver详解

在Android中，我们的应⽤有的时候需要对外提供数据接⼝，可以有如下⼏种⽅法：1）AIDL 2）Broadcast 3）ContentProvider。

使⽤AIDL需要我们编写AIDL接⼝以及实现，⽽且对⽅也要有相应的接⼝描述，有点⿇烦；使⽤Broadcast，我们不需要任何接⼝描述，只要协议⽂档就可以了，但是有点不好就是，这种⽅式不直接⽽且是异步的；使⽤ContentProvider我们不需要接⼝描述，只需要知道协议，同时这种⽅式是同步的，使⽤⽅便。下⾯是ContentProvider实现：

package com.backgroundservice;

import android.content.ContentProvider;import android.content.ContentValues;import android.content.UriMatcher;import android.database.Cursor;

import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteQueryBuilder;import android.NET.Uri;import android.util.Log;

/**

* TODO *

* @author zengpeng

* @version 1.0 Create At : 2010-3-18 下午02:52:40 */

public class TestContentProvider extends ContentProvider { private SQLiteDatabase mDb;

private DatabaseHelper mDbHelper = null;

private static final String DATABASE_NAME = \"rssitems.db\";

private static final String DATABASE_TABLE_NAME = \"rssItems\"; private static final int DB_VERSION = 1; private static final int ALL_MESSAGES = 1;

private static final int SPECIFIC_MESSAGE = 2;

// Set up our URL matchers to help us determine what an // incoming URI parameter is.

private static final UriMatcher URI_MATCHER; static {

URI_MATCHER = new UriMatcher(UriMatcher.NO_MATCH); URI_MATCHER.addURI(\"test\

URI_MATCHER.addURI(\"test\ }

// Here's the public URI used to query for RSS items. public static final Uri CONTENT_URI = Uri .parse(\"content://test/item\");

// Here are our column name constants, used to query for field values. public static final String ID = \"_id\";

public static final String NAME = \"NAME\"; public static final String VALUE = \"VALUE\";

public static final String DEFAULT_SORT_ORDER = ID + \" DESC\"; private static class DatabaseHelper extends AbstractDatabaseHelper { @Override

protected String[] createDBTables() { // TODO Auto-generated method stub

String sql = \"CREATE TABLE \" + DATABASE_TABLE_NAME + \"(\" + ID + \" INTEGER PRIMARY KEY AUTOINCREMENT, \" + NAME + \" TEXT,\" + VALUE + \" TEXT);\"; return new String[] { sql }; }

@Override

protected String[] dropDBTables() {

// TODO Auto-generated method stub return null; }

@Override

protected String getDatabaseName() { // TODO Auto-generated method stub return DATABASE_NAME; }

@Override

protected int getDatabaseVersion() { // TODO Auto-generated method stub return DB_VERSION; }

@Override

protected String getTag() {

// TODO Auto-generated method stub

return TestContentProvider.class.getSimpleName(); } }

/** * */

public TestContentProvider() {

// TODO Auto-generated constructor stub }

/*

* (non-Javadoc) *

* @see android.content.ContentProvider#delete(android.Net.Uri, * Java.lang.String, java.lang.String[]) */

@Override

public int delete(Uri uri, String selection, String[] selectionArgs) { // NOTE Argument checking code omitted. Check your parameters!

int rowCount = mDb.delete(DATABASE_TABLE_NAME, selection, selectionArgs); // Notify any listeners and return the deleted row count. getContext().getContentResolver().notifyChange(uri, null); return rowCount; }

/*

* (non-Javadoc) *

* @see android.content.ContentProvider#getType(android.net.Uri) */

@Override

public String getType(Uri uri) {

switch (URI_MATCHER.match(uri)) { case ALL_MESSAGES:

return \"vnd.android.cursor.dir/rssitem\"; // List of items. case SPECIFIC_MESSAGE:

return \"vnd.android.cursor.item/rssitem\"; // Specific item. default: return null; } }

/*

* (non-Javadoc) *

* @see android.content.ContentProvider#insert(android.net.Uri, * android.content.ContentValues) */

@Override

public Uri insert(Uri uri, ContentValues values) {

// NOTE Argument checking code omitted. Check your parameters! Check that // your row addition request succeeded! long rowId = -1;

rowId = mDb.insert(DATABASE_TABLE_NAME, NAME, values);

Uri newUri = Uri.withAppendedPath(CONTENT_URI, \"\"+rowId);

Log.i(\"TestContentProvider\ // Notify any listeners and return the URI of the new row.

getContext().getContentResolver().notifyChange(CONTENT_URI, null); return newUri; }

/*

* (non-Javadoc) *

* @see android.content.ContentProvider#onCreate() */

@Override

public boolean onCreate() {

// TODO Auto-generated method stub try {

mDbHelper = new DatabaseHelper(); mDbHelper.open(getContext()); mDb = mDbHelper.getMDb(); }catch(Exception e){ e.printStackTrace(); }

return true; }

/*

* (non-Javadoc) *

* @see android.content.ContentProvider#query(android.net.Uri, * java.lang.String[], java.lang.String, java.lang.String[], * java.lang.String) */

public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {

// We won't bother checking the validity of params here, but you should! // SQLiteQueryBuilder is the helper class that creates the // proper SQL syntax for us.

SQLiteQueryBuilder qBuilder = new SQLiteQueryBuilder(); // Set the table we're querying.

qBuilder.setTables(DATABASE_TABLE_NAME); // If the query ends in a specific record number, we're // being asked for a specific record, so set the

// WHERE clause in our query.

if((URI_MATCHER.match(uri)) == SPECIFIC_MESSAGE){ qBuilder.appendWhere(\"_id=\" + uri.getLastPathSegment());

Log.i(\"TestContentProvider\ }

// Make the query.

Cursor c = qBuilder.query(mDb, projection, selection,

selectionArgs, null, null,

sortOrder);

Log.i(\"TestContentProvider\

c.setNotificationUri(getContext().getContentResolver(), uri); return c; }

/*

* (non-Javadoc) *

* @see android.content.ContentProvider#update(android.net.Uri, * android.content.ContentValues, java.lang.String, java.lang.String[]) */

@Override

public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {

// NOTE Argument checking code omitted. Check your parameters!

int updateCount = mDb.update(DATABASE_TABLE_NAME, values, selection, selectionArgs); // Notify any listeners and return the updated row count. getContext().getContentResolver().notifyChange(uri, null); return updateCount; }}

配⽂件如下：

在客户端中可以使⽤如下⽅法进⾏调⽤：

ContentValues values = new ContentValues();

values.put(TestContentProvider.NAME, \"testname1\"); values.put(TestContentProvider.VALUE, \"testvalu1e\");

Uri newAddUri = TestActivity.this.getContentResolver().insert(TestContentProvider.CONTENT_URI, values);

Cursor c = TestActivity.this.managedQuery(newAddUri, new String[]{TestContentProvider.NAME}, null, null, null); Log.i(\"TestActivity\ if(c.moveToNext()) {

Log.i(\"TestActivity\ }

上⾯的代码是先进⾏插⼊，然后进⾏查询并打印。就是如此简单，所有的应⽤如果需要都可以对外⽅便的提供数据接⼝，同时其他应⽤也可以很⽅便的进⾏调⽤。

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