Android组件系列——Content Provider

Content Provider

跨进程共享数据的标准方式

与SharedPreferences存储中的全局可读可写操作模式不同的是，Content Provider可选择只对某一部分数据进行共享，从而保证数据的安全性

ContentResolver

不同于SQLiteDatabase,ContentResolver中的增删改查方法均不接收表名参数，而是使用一个Uri的参数代替，这个参数被称作内容URI
内容URI：内容提供者中的数据的唯一标识符，由两部分组成：authority和path
authority：给不同应用程序做区分，为避免冲突，采用包名命名
path：给同一应用程序中不同表做区分，通常都会添加到authority后面

内容URI标准格式：content://包名/表名
只访问某表中指定id的数据：content://包名/表名/id
匹配任意表的内容：content://包名/*
匹配指定表的任意一行数据：content://包名/表名/#
*：表示匹配任意长度的任意字符
#：表示匹配任意长度的任意数字

获取Uri实例：Uri uri = new Uri.parse(内容URI); ****

//获取实例
ContentResolver resolver = Context.getContentResolver()
//增
Uri insert(Uri url, ContentValues values)	
//删
int delete(Uri url, String where, String[] selectionArgs)	
//改
int update(Uri uri, ContentValues values, String where, String[] selectionArgs)  
//查
Cursor query(Uri uri, String[] projection, Bundle queryArgs,
            CancellationSignal cancellationSignal)

基础使用

ContentProvider的创建

public class DatabaseProvider extends ContentProvider {
    public static final int BOOK_DIR = 0;
    public static final int BOOK_ITEM = 1;
    public static final String authority = "com.example.provider";
    private static UriMatcher uriMatcher;
    private MyDatabaseHelper dbHelper;	//内容提供器数据库支持
    static {
        uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        uriMatcher.addURI(authority, "book", BOOK_DIR);
        uriMatcher.addURI(authority, "book/#", BOOK_ITEM);
    }
    @Override
    public boolean onCreate() {
        //创建内容提供器要使用的数据库
        dbHelper = new MyDatabaseHelper(getContext(), "BookStore.db", null, 2);
        //必须返回true，否则内容提供器无法被使用
        return true;
    }
    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
        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;
        }
        return cursor;
    }
    @Override
    public Uri insert(Uri uri, ContentValues values) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        Uri uriReturn = null;
        long newBookId = db.insert("Book", null, values);
        switch (uriMatcher.match(uri)) {
            case BOOK_DIR:
                uriReturn = Uri.parse("content://" + authority + "/book/" +
                        newBookId);
                break;
            case BOOK_ITEM:
                uriReturn = Uri.parse("content://" + authority + "/book/" +
                        newBookId);
                break;
        }
        return uriReturn;
    }
    @Override
    public int update(Uri uri, ContentValues values, String selection,
                      String[] selectionArgs) {
        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;
        }
        return updatedRows;
    }
    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        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;
        }
        return deletedRows;
    }
    @Override
    //Uri对象所对应的MIME类型
    //必须以vnd开头
	//如内容URI以路径结尾，后接android.cursor.dir/；如以id结尾，后接android.cursor.item/
	//最后接vnd.[authority].[path]
    public String getType(Uri uri) {
        switch (uriMatcher.match(uri)) {
            case BOOK_DIR:
                return "vnd.android.cursor.dir/vnd." + authority + ".book";
            case BOOK_ITEM:
                return "vnd.android.cursor.item/vnd." + authority + ".book";
        }
        return null;
    }
}

ContentProvider的访问

public void insert(View view) {	
    // 得到内容提供者的解析器
    ContentResolver resolver = getContentResolver();	
    //获得内容提供者的uri,注意uri格式
    Uri uri = Uri.parse("content://com.example.provider/book");
    //创建ContentValues对象,目的是创建一个空的set集合,用于存储数据
    ContentValues values = new ContentValues();				
    values.put("name", "zhangsan");							
    values.put("money", 10000);
    // 通过内容解析器让内容提供者添加一条数据
    resolver.insert(uri, values);		
    //注册内容观察者 
    resolver.registerContentObserver(uri, true, new ContentObserver(new Handler()) {		
        @Override
        public void onChange(boolean selfChange) {
            super.onChange(selfChange);
        }
    });
}