一、ContentProvider简介
   当应用继承ContentProvider类，并重写该类用于提供数据和存储数据的方法，就可以向其他应用共享其数据。虽然使用其他方法也可以对外共享数据，但数据访问方式会因数据存储的方式而不同，如：采用文件方式对外共享数据，需要进行文件操作读写数据；采用sharedpreferences共享数据，需要使用sharedpreferences API读写数据。而使用ContentProvider共享数据的好处是统一了数据访问方式。

二、Uri类简介
   Uri代表了要操作的数据，Uri主要包含了两部分信息：1.需要操作的ContentProvider ，2.对ContentProvider中的什么数据进行操作，一个Uri由以下几部分组成：

   1.scheme：ContentProvider（内容提供者）的scheme已经由Android所规定为：content://。
   2.主机名（或Authority）：用于唯一标识这个ContentProvider，外部调用者可以根据这个标识来找到它。
   3.路径（path）：可以用来表示我们要操作的数据，路径的构建应根据业务而定，如下：
•       要操作contact表中id为10的记录，可以构建这样的路径:/contact/10
•       要操作contact表中id为10的记录的name字段:/contact/10/name
•       要操作contact表中的所有记录，可以构建这样的路径:/contact
要操作的数据不一定来自数据库，也可以是文件等他存储方式，如下:
要操作xml文件中contact节点下的name节点，可以构建这样的路径：/contact/name
如果要把一个字符串转换成Uri，可以使用Uri类中的parse()方法，如下：
Uri uri = Uri.parse("content://com.changcheng.provider.contactprovider/contact")

三、UriMatcher、ContentUrist和ContentResolver简介
   因为Uri代表了要操作的数据，所以我们很经常需要解析Uri，并从Uri中获取数据。Android系统提供了两个用于操作Uri的工具类，分别为UriMatcher 和ContentUris 。掌握它们的使用，会便于我们的开发工作。

   UriMatcher：用于匹配Uri，它的用法如下：
   1.首先把你需要匹配Uri路径全部给注册上，如下：
   //常量UriMatcher.NO_MATCH表示不匹配任何路径的返回码(-1)。
   UriMatcher  uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
   //如果match()方法匹配content://com.changcheng.sqlite.provider.contactprovider/contact路径，返回匹配码为1
   uriMatcher.addURI(“com.changcheng.sqlite.provider.contactprovider”, “contact”, 1);//添加需要匹配uri，如果匹配就会返回匹配码
   //如果match()方法匹配 content://com.changcheng.sqlite.provider.contactprovider/contact/230路径，返回匹配码为2
   uriMatcher.addURI(“com.changcheng.sqlite.provider.contactprovider”, “contact/#”, 2);//#号为通配符

   2.注册完需要匹配的Uri后，就可以使用uriMatcher.match(uri)方法对输入的Uri进行匹配，如果匹配就返回匹配码，匹配码是调用 addURI()方法传入的第三个参数，假设匹配 content://com.changcheng.sqlite.provider.contactprovider/contact路径，返回的匹配码为1。

   ContentUris：用于获取Uri路径后面的ID部分，它有两个比较实用的方法：
•       withAppendedId(uri, id)用于为路径加上ID部分
•       parseId(uri)方法用于从路径中获取ID部分

   ContentResolver：当外部应用需要对ContentProvider中的数据进行添加、删除、修改和查询操作时，可以使用 ContentResolver 类来完成，要获取ContentResolver 对象，可以使用Activity提供的getContentResolver()方法。 ContentResolver使用insert、delete、update、query方法，来操作数据。

四、ContentProvider示例程序
Manifest.xml中的代码：

需要在中为provider进行注册！！！！
首先定义一个数据库的工具类：

public class RuiXin {
 
        public static final String DBNAME = "ruixinonlinedb"; 
        public static final String TNAME = "ruixinonline";
        public static final int VERSION = 3;
         
        public static String TID = "tid";
        public static final String EMAIL = "email";
        public static final String USERNAME = "username";
        public static final String DATE = "date";
        public static final String SEX = "sex";
         
         
        public static final String AUTOHORITY = "com.ruixin.login";
        public static final int ITEM = 1;
        public static final int ITEM_ID = 2;
         
        public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.ruixin.login";
        public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.ruixin.login";
         
        public static final Uri CONTENT_URI = Uri.parse("content://" + AUTOHORITY + "/ruixinonline");
}

然后创建一个数据库：

public class DBlite extends SQLiteOpenHelper {
        public DBlite(Context context) {
                super(context, RuiXin.DBNAME, null, RuiXin.VERSION);
                // TODO Auto-generated constructor stub
        }
        @Override
        public void onCreate(SQLiteDatabase db) {
                // TODO Auto-generated method stub
                        db.execSQL("create table "+RuiXin.TNAME+"(" +
                                RuiXin.TID+" integer primary key autoincrement not null,"+
                                RuiXin.EMAIL+" text not null," +
                                RuiXin.USERNAME+" text not null," +
                                RuiXin.DATE+" interger not null,"+
                                RuiXin.SEX+" text not null);");
        }
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
                // TODO Auto-generated method stub
        }
        public void add(String email,String username,String date,String sex){
                SQLiteDatabase db = getWritableDatabase();
                ContentValues values = new ContentValues();
                values.put(RuiXin.EMAIL, email);
                values.put(RuiXin.USERNAME, username);
                values.put(RuiXin.DATE, date);
                values.put(RuiXin.SEX, sex);
                db.insert(RuiXin.TNAME,"",values);
        }
}

接着创建一个Myprovider.java对数据库的接口进行包装：

public class MyProvider extends ContentProvider{
 
        DBlite dBlite;
        SQLiteDatabase db;
         
        private static final UriMatcher sMatcher;
        static{
                sMatcher = new UriMatcher(UriMatcher.NO_MATCH);
                sMatcher.addURI(RuiXin.AUTOHORITY,RuiXin.TNAME, RuiXin.ITEM);
                sMatcher.addURI(RuiXin.AUTOHORITY, RuiXin.TNAME+"/#", RuiXin.ITEM_ID);
 
        }
        @Override
        public int delete(Uri uri, String selection, String[] selectionArgs) {
                // TODO Auto-generated method stub
                db = dBlite.getWritableDatabase();
                int count = 0;
                switch (sMatcher.match(uri)) {
                case RuiXin.ITEM:
                        count = db.delete(RuiXin.TNAME,selection, selectionArgs);
                        break;
                case RuiXin.ITEM_ID:
                        String id = uri.getPathSegments().get(1);
                        count = db.delete(RuiXin.TID, RuiXin.TID+"="+id+(!TextUtils.isEmpty(RuiXin.TID="?")?"AND("+selection+')':""), selectionArgs);
                    break;
                default:
                        throw new IllegalArgumentException("Unknown URI"+uri);
                }
                getContext().getContentResolver().notifyChange(uri, null);
                return count;
        }
 
        @Override
        public String getType(Uri uri) {
                // TODO Auto-generated method stub
                switch (sMatcher.match(uri)) {
                case RuiXin.ITEM:
                        return RuiXin.CONTENT_TYPE;
                case RuiXin.ITEM_ID:
                    return RuiXin.CONTENT_ITEM_TYPE;
                default:
                        throw new IllegalArgumentException("Unknown URI"+uri);
                }
        }
 
        @Override
        public Uri insert(Uri uri, ContentValues values) {
                // TODO Auto-generated method stub
                 
                db = dBlite.getWritableDatabase();
                long rowId;
                if(sMatcher.match(uri)!=RuiXin.ITEM){
                        throw new IllegalArgumentException("Unknown URI"+uri);
                }
                rowId = db.insert(RuiXin.TNAME,RuiXin.TID,values);
                   if(rowId>0){
                           Uri noteUri=ContentUris.withAppendedId(RuiXin.CONTENT_URI, rowId);
                           getContext().getContentResolver().notifyChange(noteUri, null);
                           return noteUri;
                   }
                   throw new IllegalArgumentException("Unknown URI"+uri);
        }
 
        @Override
        public boolean onCreate() {
                // TODO Auto-generated method stub
                this.dBlite = new DBlite(this.getContext());
//                db = dBlite.getWritableDatabase();
//                return (db == null)?false:true;
                return true;
        }
 
        @Override
        public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
                // TODO Auto-generated method stub
                db = dBlite.getWritableDatabase();                
                Cursor c;
                Log.d("-------", String.valueOf(sMatcher.match(uri)));
                switch (sMatcher.match(uri)) {
                case RuiXin.ITEM:
                        c = db.query(RuiXin.TNAME, projection, selection, selectionArgs, null, null, null);
                 
                        break;
                case RuiXin.ITEM_ID:
                        String id = uri.getPathSegments().get(1);
                        c = db.query(RuiXin.TNAME, projection, RuiXin.TID+"="+id+(!TextUtils.isEmpty(selection)?"AND("+selection+')':""),selectionArgs, null, null, sortOrder);
                    break;
                default:
                        Log.d("!!!!!!", "Unknown URI"+uri);
                        throw new IllegalArgumentException("Unknown URI"+uri);
                }
                c.setNotificationUri(getContext().getContentResolver(), uri);
                return c;
        }
        @Override
        public int update(Uri uri, ContentValues values, String selection,
                        String[] selectionArgs) {
                // TODO Auto-generated method stub
                return 0;
        }
}

最后创建测试类：

public class Test extends Activity {
    /** Called when the activity is first created. */
   private DBlite dBlite1 = new DBlite(this);;
        private ContentResolver contentResolver;
                    public void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.main);
                //先对数据库进行添加数据
            dBlite1.add(email,username,date,sex);
            //通过contentResolver进行查找
             contentResolver = TestWebviewDemo.this.getContentResolver();
            Cursor cursor = contentResolver.query(
                  RuiXin.CONTENT_URI, new String[] {
                  RuiXin.EMAIL, RuiXin.USERNAME,
                  RuiXin.DATE,RuiXin.SEX }, null, null, null);
                while (cursor.moveToNext()) {
                     Toast.makeText(
                    TestWebviewDemo.this,
                    cursor.getString(cursor.getColumnIndex(RuiXin.EMAIL))
                            + " "
                            + cursor.getString(cursor.getColumnIndex(RuiXin.USERNAME))
                            + " "
                            + cursor.getString(cursor.getColumnIndex(RuiXin.DATE))
                            + " "
                            + cursor.getString(cursor.getColumnIndex(RuiXin.SEX)),
                           Toast.LENGTH_SHORT).show();
                     }
                   startManagingCursor(cursor);  //查找后关闭游标
            }
        }

注：上面是在一个程序中进行的测试，也可以再新建一个工程来模拟一个新的程序，然后将上面查询的代码加到新的程序当中！这样就模拟了contentprovider的数据共享功能了！
新建个工程：TestProvider
创建一个测试的activity

public class Test extends Activity {
    /** Called when the activity is first created. */
        private ContentResolver contentResolver;
                    public void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.main);
               
            //通过contentResolver进行查找
              contentResolver = TestWebviewDemo.this.getContentResolver();                     
             Cursor cursor = contentResolver.query(
                RuiXin.CONTENT_URI, new String[] {
                RuiXin.EMAIL, RuiXin.USERNAME,
                RuiXin.DATE,RuiXin.SEX }, null, null, null);
            while (cursor.moveToNext()) {
               Toast.makeText(TestWebviewDemo.this,
                       cursor.getString(cursor.getColumnIndex(RuiXin.EMAIL))
                       + " "
                       + cursor.getString(cursor.getColumnIndex(RuiXin.USERNAME))
                       + " "
                       + cursor.getString(cursor.getColumnIndex(RuiXin.DATE))
                       + " "
                       + cursor.getString(cursor.getColumnIndex(RuiXin.SEX)),
                       Toast.LENGTH_SHORT).show();
                   }
                   startManagingCursor(cursor);  //查找后关闭游标
            }
        }

运行此程序就能实现共享数据查询了！

注：新建的程序中的manifest.xml中不需要对provider进行注册，直接运行就行，否则会报错！

ITPub博客

Android ContentProvider总结[转]

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