安卓应用程序默认是无法获取到其他程序的数据，这是安卓安全学的基石(沙盒原理)。但是经常我们需要给其他应用分享数据，内容提供者就是一个这种可以分享数据给其他应用的接口。 可以简单的理解为，内容提供者就是一个可以在不同应用程序间共享数据的组件，相当于一个中间人，一个程序把数据暴露给这个中间人，另一个则通过这个中间人获取相应的数据.
下面的这张图片能更直观的显示:
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ContentProvider中的getContext和AndroidTestCast中的getContext方法一样，都是一个模拟的上下文，必须在该类初始化之后才会调用setContext方法将context设置成自己的成员变量中记录， 所以对于获取getContext的时候只能放在方法内，不能放到成员位置，因为在成员上时是null，而在方法内调用时该类就会已经初始化完了 -
ContentProvider中的query()后不能关闭数据库，因为其他的应用在调用该query方法时需要继续使用该返回值Cursor，所以不能关闭数据库，因为数据库关闭之后Cursor就不能用了，Cursor中保存的数据其实是数据库的一个引用，如果数据库关了Cursor就不能找到里面的数据了，Cursor.close()只是释放Cursor用到的资源。说到这里就多数一句According to Dianne Hackborn (Android framework engineer) there is no need to close the database in a content provider.以为内容提供者是因为进程启动时便加载，之后就一直存在，当进程销毁 释放资源时会去关闭数据库。 -
如果数据是
SQLiteDatabase，表中必须有一个_id的列，用来表示每条记录的唯一性。
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继承
ContentProvider,并实现相应的方法。public class NoteProvider extends ContentProvider { private static final int NOTES = 1; private static final int NOTE_ID = 2; public static final String AUTHORITY = "com.charon.demo.provider.noteprovider"; public static final String TABLE_NAME = "note"; // 定义一个名为`CONTENT_URI`必须为其指定一个唯一的字符串值，最好的方案是以类的全名称 public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/" + TABLE_NAME); // 声明一个路径的检查者，参数为Uri不匹配时的返回值 // 虽然是中间人，但也不能谁要数据我们都给，所以要检查下，只有符合我们要求的人，我们才会给他数据。 private static UriMatcher sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH); private NoteSQLiteOpenHelper mSQLiteOpenHelper; private SQLiteDatabase mSQLiteDatabase; static { // 建立匹配规则，例如发现路径为ccom.charon.demo.provider.noteprovider/note/1表示要操作note表中id为1的记录 sUriMatcher.addURI(AUTHORITY, TABLE_NAME, NOTES); sUriMatcher.addURI(AUTHORITY, TABLE_NAME + "/#", NOTE_ID); } /** * Implement this to initialize your content provider on startup. * This method is called for all registered content providers on the * application main thread at application launch time. It must not perform * lengthy operations, or application startup will be delayed. * <p/> * <p>You should defer nontrivial initialization (such as opening, * upgrading, and scanning databases) until the content provider is used * (via {@link #query}, {@link #insert}, etc). Deferred initialization * keeps application startup fast, avoids unnecessary work if the provider * turns out not to be needed, and stops database errors (such as a full * disk) from halting application launch. * <p/> * <p>If you use SQLite, {@link android.database.sqlite.SQLiteOpenHelper} * is a helpful utility class that makes it easy to manage databases, * and will automatically defer opening until first use. If you do use * SQLiteOpenHelper, make sure to avoid calling * {@link android.database.sqlite.SQLiteOpenHelper#getReadableDatabase} or * {@link android.database.sqlite.SQLiteOpenHelper#getWritableDatabase} * from this method. (Instead, override * {@link android.database.sqlite.SQLiteOpenHelper#onOpen} to initialize the * database when it is first opened.) * * @return true if the provider was successfully loaded, false otherwise */ @Override public boolean onCreate() { mSQLiteOpenHelper = new NoteSQLiteOpenHelper(getContext()); return true; } /** * 内容提供者暴露的查询的方法. */ @Override public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { mSQLiteDatabase = mSQLiteOpenHelper.getReadableDatabase(); Cursor cursor; // 1.重要的事情 ,检查 uri的路径. switch (sUriMatcher.match(uri)) { case NOTES: break; case NOTE_ID: String id = uri.getLastPathSegment(); if (TextUtils.isEmpty(selection)) { selection = selection + "_id = " + id; } else { selection = selection + " and " + "_id = " + id; } break; default: throw new IllegalArgumentException("UnKnown Uri" + uri); break; } cursor = mSQLiteDatabase.query(TABLE_NAME, projection, selection, selectionArgs, null, null, sortOrder); if (cursor != null) { cursor.setNotificationUri(getContext().getContentResolver(), uri); } return cursor; } /** * Implement this to handle requests for the MIME type of the data at the * given URI. The returned MIME type should start with * <code>vnd.android.cursor.item</code> for a single record, * or <code>vnd.android.cursor.dir/</code> for multiple items. * This method can be called from multiple threads, as described in * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes * and Threads</a>. * <p/> * <p>Note that there are no permissions needed for an application to * access this information; if your content provider requires read and/or * write permissions, or is not exported, all applications can still call * this method regardless of their access permissions. This allows them * to retrieve the MIME type for a URI when dispatching intents. * * @param uri the URI to query. * @return a MIME type string, or {@code null} if there is no type. */ @Override public String getType(Uri uri) { // 注释说的很清楚了，下面是常用的格式 // 单个记录的IMEI类型 vnd.android.cursor.item/vnd.<yourcompanyname>.<contenttype> // 多个记录的IMEI类型 vnd.android.cursor.dir/vnd.<yourcompanyname>.<contenttype> switch (sUriMatcher.match(uri)) { case NOTE_ID: // 如果uri为 content://com.charon.demo.noteprovider/note/1 return "vnd.android.cursor.item/vnd.charon.note"; case NOTES: return "vnd.android.cursor.dir/vnd.charon.note"; default: return null; } // 这个MIME类型的作用是要匹配AndroidManifest.xml文件<activity>标签下<intent-filter>标签的子标签<data>的属性android:mimeType。 // 如果不一致，则会导致对应的Activity无法启动。 } @Override public Uri insert(Uri uri, ContentValues values) { mSQLiteDatabase = mSQLiteOpenHelper.getWritableDatabase(); switch (sUriMatcher.match(uri)) { case NOTES: break; case NOTE_ID: break; default: throw new IllegalArgumentException("UnKnown Uri" + uri); break; } long rowId = mSQLiteDatabase.insert(TABLE_NAME, null, values); if (rowId > 0) { Uri noteUri = ContentUris.withAppendedId(CONTENT_URI, rowId); getContext().getContentResolver().notifyChange(noteUri, null); return noteUri; } return null; } @Override public int delete(Uri uri, String selection, String[] selectionArgs) { mSQLiteDatabase = mSQLiteOpenHelper.getWritableDatabase(); switch (sUriMatcher.match(uri)) { case NOTES: break; case NOTE_ID: String id = uri.getLastPathSegment(); if (TextUtils.isEmpty(selection)) { selection = selection + "_id = " + id; } else { selection = selection + " and " + "_id = " + id; } break; default: throw new IllegalArgumentException("UnKnown Uri" + uri); break; } int count = mSQLiteDatabase.delete(TABLE_NAME, selection, selectionArgs); getContext().getContentResolver().notifyChange(uri, null); return count; } @Override public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) { switch (sUriMatcher.match(uri)) { case NOTES: break; case NOTE_ID: break; default: throw new IllegalArgumentException("UnKnown Uri" + uri); break; } mSQLiteDatabase = mSQLiteOpenHelper.getWritableDatabase(); int update = mSQLiteDatabase.update(TABLE_NAME, values, selection, selectionArgs); return update; }
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在清单文件中进行注册，并且指定其authorities
<provider android:name="com.charon.demo.provider.NoteProvider" android:authorities="com.charon.demo.provider.noteprovider" >
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使用内容提供者获取数据，使用
ContentResolver去操作ContentProvider,ContentResolver用于管理ContentProvider实例， 并且可实现找到指定的ContentProvider并获取里面的数据public void query(View view){ //得到内容提供者的解析器 中间人 ContentResolver resolver = getContentResolver(); Cursor cursor = resolver.query(NoteProvider.CONTENT_URI, null, null, null, null); while(cursor.moveToNext()){ String name = cursor.getString(cursor.getColumnIndex("name")); int id = cursor.getInt(cursor.getColumnIndex("id")); float money = cursor.getFloat(cursor.getColumnIndex("money")); System.out.println("id="+id+",name="+name+",money="+money); } cursor.close(); } public void insert(View view){ ContentResolver resolver = getContentResolver(); ContentValues values = new ContentValues(); values.put("name", "买洗头膏"); values.put("money", 22.58f); resolver.insert(NoteProvider.CONTENT_URI, values); } public void update(View view){ ContentResolver resolver = getContentResolver(); ContentValues values = new ContentValues(); values.put("name", "买洗头膏"); values.put("money", 42.58f); resolver.update(NoteProvider.CONTENT_URI, values, "name=?", new String[]{"买洗头膏"}); } public void delete(View view){ ContentResolver resolver = getContentResolver(); resolver.delete(NoteProvider.CONTENT_URI, "name=?", new String[]{"买洗头膏"}); }
内容观察者的原理：
How a content provider actually stores its data under the covers is up to its designer. But all content providers implement a common interface for querying the provider and returning results — as well as for adding, altering, and deleting data. It's an interface that clients use indirectly, most generally through ContentResolver objects. You get a ContentResolver by calling getContentResolver() from within the implementation of an Activity or other application component: You can then use the ContentResolver's methods to interact with whatever content providers you're interested in.
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一方使用内容观察者去观察变化
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); ContentResolver resolver = getContentResolver(); resolver.registerContentObserver(NoteProvider.CONTENT_URI, true, new NoteObserver(new Handler())); } private class NoteObserver extends ContentObserver { public NoteObserver(Handler handler) { super(handler); } //当观察到数据发生变化的时候 会执行onchange方法. @Override public void onChange(boolean selfChange) { super.onChange(selfChange); Log.i(TAG,"发现有新的短信产生了..."); //1.利用内容提供者 中间人 获取用户的短信数据. ContentResolver resolver = getContentResolver(); // .. 重新查询 cursor = ...; cursor.close(); } }
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一方在发生变化的时候去发送改变的消息 对于一些系统的内容提供者内部都实现了该步骤，如果是自己写程序想要暴露就必须要加上该代码。
getContext().getContentResolver().notifyChange(uri, null);
- 邮箱 ：charon.chui@gmail.com
- Good Luck!