Android自定义Content Provider及使用

先看看官网API的介绍：

Content providers are one of the primary building blocks of Android applications, providing content to applications. 

Content providers是Android app的基石之一。

They encapsulate data and provide it to applications through the single ContentResolver interface.

它们封装了数据，提供了惟一一个ContentResolver接口。

 A content provider is only required if you need to share data between multiple applications. For example, the contacts data is used by multiple applications and must be stored in a content provider.

只有当你须要在不一样的APP之间分享数据，你才有必要建立一个的 content provider。好比，系统的联系人数据常常被许多APP所使用，因此必须存放在 content provider里。

 If you don't need to share data amongst multiple applications you can use a database directly via SQLiteDatabase.
若是你不须要在不一样的APP之间分享数据，你能够直接使用SQLite数据库。

When a request is made via a ContentResolver the system inspects the authority of the given URI and passes the request to the content provider registered with the authority. 

当APP经过ContentResolver发起一个对content provider的数据请求时，系统会根据请求里的URI的身份标识将请求递交给对应的content provider

The content provider can interpret the rest of the URI however it wants. The UriMatcher class is helpful for parsing URIs.
收到请求的content provider能够自行翻译URI的剩余内容，UriMatcher类对此大有帮助。

The primary methods that need to be implemented are:
若是继承了ContentProvider类，须要实现如下方法。

onCreate() which is called to initialize the provider 初始化
query(Uri, String[], String, String[], String) which returns data to the caller 返回请求的数据
insert(Uri, ContentValues) which inserts new data into the content provider 插入新数据
update(Uri, ContentValues, String, String[]) which updates existing data in the content provider 修改数据
delete(Uri, String, String[]) which deletes data from the content provider 删除数据
getType(Uri) which returns the MIME type of data in the content provider 返回数据类型

自定义一个java类并继承自ContentProvider类：

public class BookProvider extends ContentProvider {

    public static final String PROVIDER_NAME = "com.hong.app.contentproviderexample.Books";

    public static final String PROVIDER_CONTENT_STRING = "content://" + PROVIDER_NAME + "/books";
    public static final Uri CONTENT_URI = Uri.parse(PROVIDER_CONTENT_STRING);
    static final String _ID = "_id";
    static final String TITLE = "title";
    static final String ISBN = "isbn";

    static final int BOOKS = 1;
    static final int BOOK_ID = 2;

    private static final UriMatcher uriMatcher;

    static {
        uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        uriMatcher.addURI(PROVIDER_NAME, "books", BOOKS);
        uriMatcher.addURI(PROVIDER_NAME, "book/#", BOOK_ID);
    }

    //--FOR DATABASE USE
    SQLiteDatabase booksDB;
    static final String DATABASE_NAME = "Books";
    static final String DATABASE_TABLE = "titles";
    static final int DATABASE_VERSION = 1;
    static final String DATABASE_CREATE = "create table " + DATABASE_TABLE + "(_id integer primary key autoincrement, title text not null,isbn text not null);";

    private static class DatabaseHelper extends SQLiteOpenHelper {

        DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(DATABASE_CREATE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            db.execSQL("DROP TABLE IF EXISTS titles");
            onCreate(db);
        }
    }

    @Override
    public boolean onCreate() {
        Context context = getContext();
        DatabaseHelper databaseHelper = new DatabaseHelper(context);
        booksDB = databaseHelper.getWritableDatabase();
        return (booksDB == null) ? false : true;
    }

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

        SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
        queryBuilder.setTables(DATABASE_TABLE);

        if (uriMatcher.match(uri) == BOOK_ID) {
            queryBuilder.appendWhere(_ID + " = " + uri.getPathSegments().get(1));
        }

        if (sortOrder == null || sortOrder == "") {
            sortOrder = TITLE;
        }

        Cursor cursor = queryBuilder.query(
                booksDB,
                projection,
                selection,
                selectionArgs,
                null,
                null,
                sortOrder
        );

        cursor.setNotificationUri(getContext().getContentResolver(), uri);

        return cursor;
    }

    @Override
    public String getType(Uri uri) {
        switch (uriMatcher.match(uri)) {
            case BOOKS:
                return "vnd.android.cursor.dir/vnd.example.administrator.books";

            case BOOK_ID:
                return "vnd.android.cursor.item/vnd.example.administrator.books";

            default:
                throw new IllegalArgumentException("Unsupported URI : " + uri);
        }
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        long rowID = booksDB.insert(DATABASE_TABLE, "", values);

        if (rowID > 0) {
            Uri _uri = ContentUris.withAppendedId(CONTENT_URI, rowID);
            getContext().getContentResolver().notifyChange(_uri, null);
            return _uri;
        } else {
            // throw new SQLException("Failed to insert row into " + uri);
            return null;
        }

    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        int count = 0;
        switch (uriMatcher.match(uri)) {
            case BOOKS:
                count = booksDB.delete(DATABASE_TABLE, selection, selectionArgs);
                break;

            case BOOK_ID:
                String id = uri.getPathSegments().get(1);
                count = booksDB.delete(DATABASE_TABLE, _ID + "=" + id + (!TextUtils.isEmpty(selection) ? " AND (" + selection + ')' : ""), selectionArgs);
                break;
            default:
                throw new IllegalArgumentException("UnKnown URI : " + uri);
        }
        getContext().getContentResolver().notifyChange(uri, null);

        return count;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        int count = 0;
        switch (uriMatcher.match(uri)) {
            case BOOKS:
                count = booksDB.update(DATABASE_TABLE, values, selection, selectionArgs);
                break;
            case BOOK_ID:
                count = booksDB.update(DATABASE_TABLE, values, _ID + "=" + uri.getPathSegments().get(1) + (!TextUtils.isEmpty(selection) ? " AND (" + selection + ')' : ""), selectionArgs);
                break;
            default:
                throw new IllegalArgumentException("UnKnown URI : " + uri);
        }

        getContext().getContentResolver().notifyChange(uri, null);
        return count;
    }
}

主要用到的类：  UriMatcher SQLiteDatabase SQLiteOpenHelper

主要用到的方法：重写了ContentProvider类的6个方法—— update，delete，onCreate,query,getType,insert; uriMatcher . match ( uri ) getContext () getContentResolver () notifyChange ( uri , null ) getPathSegments ()

关键：以上自定义的content provider 用SQLite的方式保存数据，用    UriMatcher 类来核对传入的uri进而进行对应的操做。

使用自定义的content provider:

private void addContent() {
        ContentValues values = new ContentValues();
        values.put(
                BookProvider.TITLE,
                titleEditText.getText().toString()
        );
        values.put(
                BookProvider.ISBN,
                ISBNEditText.getText().toString()
        );
        Uri uri = getContentResolver().insert(BookProvider.CONTENT_URI, values);
        Toast.makeText(getBaseContext(), "Add book: \n" + uri.toString(), Toast.LENGTH_LONG).show();
    }


    private void retrieveAll() {

        Uri allTitles = Uri.parse(BookProvider.PROVIDER_CONTENT_STRING);
        Cursor cursor;

        CursorLoader cursorLoader = new CursorLoader(
                getBaseContext(),
                allTitles,
                null,
                null,
                null,
                "title desc"
        );
        cursor = cursorLoader.loadInBackground();

        StringBuilder builder = new StringBuilder();
        if (cursor!=null) {
            if (cursor.moveToFirst()) {
                do {
                    builder.append(cursor.getString(BookProvider.BOOK_ID) + ","
                            + cursor.getString(cursor.getColumnIndex(BookProvider.TITLE)) + ","
                            + cursor.getString(cursor.getColumnIndex(BookProvider.ISBN)) + "\n");
                } while (cursor.moveToNext());

                String content = builder.toString();

                new AlertDialog.Builder(this)
                        .setTitle("Books")
                        .setMessage("All books:\n" + content)
                        .show();

            }
        }
    }

注意事项：

1. 记得在 AndroidManifest.xml中声明provider。而且android:exported值设为true

<provider
        android:exported="true"
        android:name=".BookProvider"
        android:authorities="com.hong.app.contentproviderexample.Books">
    </provider>

    2.声明权限

<uses-permission android:name="com.hong.app.contentproviderexample.Books" />

源码：https://github.com/freewheel70/ContentProviderExample