Android四大組件——ContentProvider的增刪改查和優化

ContentProvider的增刪改查和優化

事先說明：

ContentProvider步驟：創數據庫，寫規則匹配，配置manifests，另外一個應用使用

其實ContentProvider就是：在一個匹配器中寫入本身寫好的匹配規則，並對外提供寫好的匹配規則供使用，剩下的就是增刪改查的處理
細節處理：

在增刪改查中的查詢中，是沒有cursor.getBoolean這個方法的，因此要對數據庫中獲取布爾值進行處理：

msg.setFlag(cursor.getInt(cursor.getColumnIndex("flag")) != 0);

ContentProvider的增刪改查
步驟一：建立一個類繼承SQLiteOpenHelper，並用SQL語句建立一個SQLite

        public class CommonOpenHelper extends SQLiteOpenHelper {
     
        private static CommonOpenHelper helper;
     
        public static CommonOpenHelper getInstance(Context context) {
            if (helper == null) {
                helper = new CommonOpenHelper(context, "common.db", null, 1);
            }
            return helper;
        }
     
        private CommonOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
            super(context, name, factory, version);
        }
     
        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL("create table message(" +
                    "id integer primary key autoincrement, " +
                    "content varchar, " +
                    "date varchar " +
                    ")");
        }
     
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
     
        }
    }

步驟二：建立一個類繼承ContentProvider，提供增刪改查的方法

        public class MyMessageProvider extends ContentProvider {
     
        //數據庫名
        public final static String DB_MESSAGE = "message";
     
        //放置一個數據庫
        CommonOpenHelper helper;
        SQLiteDatabase db;
     
        //空白匹配器
        UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
     
        //自身的匹配規則
        final static int CODE_MESSAGE_INSERT = 0;
        final static int CODE_MESSAGE_QUERY = 1;
        final static int CODE_MESSAGE_DELETE = 2;
        final static int CODE_MESSAGE_UPDATE = 3;
     
        //主機名
        final static String authority = "com.handsome.nfcc";
        final static Uri BASE_URI = Uri.parse("content://com.handsome.nfcc");
        
        //寫入該主機名的匹配規則
        {
            matcher.addURI(authority, "message/insert", CODE_MESSAGE_INSERT);
            matcher.addURI(authority, "message/query", CODE_MESSAGE_QUERY);
            matcher.addURI(authority, "message/delete", CODE_MESSAGE_DELETE);
            matcher.addURI(authority, "message/update", CODE_MESSAGE_UPDATE);
        }
     
        //對外提供的URI
        public interface URI {
            Uri CODE_MESSAGE_INSERT = Uri.parse("content://" + authority + "/message/insert");
            Uri CODE_MESSAGE_QUERY = Uri.parse("content://" + authority + "/message/query");
            Uri CODE_MESSAGE_DELETE = Uri.parse("content://" + authority + "/message/delete");
            Uri CODE_MESSAGE_UPDATE = Uri.parse("content://" + authority + "/message/update");
        }
     
        @Override
        public boolean onCreate() {
            helper = CommonOpenHelper.getInstance(getContext());
            db = helper.getWritableDatabase();
            return false;
        }
     
        @Override
        public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
            switch (matcher.match(uri)) {
                case CODE_MESSAGE_QUERY:
                    Cursor cursor = db.query(DB_MESSAGE, projection, selection, selectionArgs, null, null, sortOrder);
                    //註冊內容觀察者，觀察數據變化
                    cursor.setNotificationUri(getContext().getContentResolver(), BASE_URI);
                    return cursor;
                default:
                    throw new IllegalArgumentException("未識別的uri" + uri);
            }
        }
     
        @Override
        public String getType(Uri uri) {
            return null;
        }
     
        @Override
        public Uri insert(Uri uri, ContentValues values) {
            switch (matcher.match(uri)) {
                case CODE_MESSAGE_INSERT:
                    long rowId = db.insert(DB_MESSAGE, null, values);
                    if (rowId == -1) {
                        //添加失敗
                        return null;
                    } else {
                        //發送內容廣播
                        getContext().getContentResolver().notifyChange(BASE_URI, null);
                        //添加成功
                        return ContentUris.withAppendedId(uri, rowId);
                    }
                default:
                    throw new IllegalArgumentException("未識別的uri" + uri);
            }
        }
     
        @Override
        public int delete(Uri uri, String selection, String[] selectionArgs) {
            switch (matcher.match(uri)) {
                case CODE_MESSAGE_DELETE:
                    int number = db.delete(DB_MESSAGE, selection, selectionArgs);
                    //發送內容廣播
                    getContext().getContentResolver().notifyChange(BASE_URI, null);
                    return number;
                default:
                    throw new IllegalArgumentException("未識別的uri" + uri);
            }
        }
     
        @Override
        public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
            switch (matcher.match(uri)) {
                case CODE_MESSAGE_UPDATE:
                    int number = db.update(DB_MESSAGE, values, selection, selectionArgs);
                    //發送內容廣播
                    getContext().getContentResolver().notifyChange(BASE_URI, null);
                    return number;
                default:
                    throw new IllegalArgumentException("未識別的uri" + uri);
            }
        }
    }

步驟三：在manifests文件中配置你所寫的ContentProvider

        <provider
                android:name=".Provider.MyMessageProvider"
                android:authorities="com.handsome.nfcc" />

步驟四：在另外一個應用中寫一個數據庫的增刪改查類，使用該ContentProvider

        public class MessageDao {
     
        /**
         * 添加數據
         */
        public static boolean insert(ContentResolver resolver, Message msg) {
            ContentValues values = new ContentValues();
            values.put("content", msg.getContent());
            values.put("date", DateUtils.showDate());
            resolver.insert(MyMessageProvider.URI.CODE_MESSAGE_INSERT, values);
            return true;
        }
     
     
        /**
         * 刪除數據
         */
        public static void delete(ContentResolver resolver, int id) {
            resolver.delete(MyMessageProvider.URI.CODE_MESSAGE_DELETE, "id = " + id, null);
        }
     
        /**
         * 刪除所有數據
         */
        public static void deleteAll(ContentResolver resolver) {
            resolver.delete(MyMessageProvider.URI.CODE_MESSAGE_DELETE, null, null);
        }
     
        /**
         * 查詢數據
         *
         * @param resolver
         * @return
         */
        public static List<Message> query(ContentResolver resolver) {
            List<Message> list = new ArrayList<>();
            Cursor cursor = resolver.query(MyMessageProvider.URI.CODE_MESSAGE_QUERY, null, null, null, null);
            while (cursor.moveToNext()) {
                Message msg = new Message();
                msg.setDate(cursor.getString(cursor.getColumnIndex("date")));
                msg.setContent(cursor.getString(cursor.getColumnIndex("content")));
                msg.setId(cursor.getInt(cursor.getColumnIndex("id")));
                list.add(0, msg);
            }
            return list;
        }
     
     
    }

ContentProvider的優化

每每在一個項目中有不少的數據庫，這個時候並非重複的寫ContentProvider代碼，而是將全部數據庫中放在一個ContentProvider中，提供一個查詢表名的方法，並對其相應的表進行操做

步驟一：ContentProvider的代碼優化（一套代碼適用多個數據庫）

    public class MyDataProvider extends ContentProvider {
     
        //數據庫名
        public final static String DB_DATA = "data";
        public final static String DB_FETCH = "fetch";
        public final static String DB_MESSAGE = "message";
     
        //放置一個數據庫
        CommonOpenHelper helper;
        SQLiteDatabase db;
     
        UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
     
        //自身的匹配規則
        final static int CODE_DATA = 0;
        final static int CODE_FETCH = 1;
        final static int CODE_MESSAGE = 2;
     
        //主機名
        final static String authority = "com.handsome.nfc";
        final static Uri BASE_URI = Uri.parse("content://com.handsome.nfc");
     
     
        //寫入該主機名的匹配規則
        {
            matcher.addURI(authority, "data", CODE_DATA);
            matcher.addURI(authority, "fetch", CODE_FETCH);
            matcher.addURI(authority, "message", CODE_MESSAGE);
        }
     
        //對外提供的URI
        public interface URI {
            Uri DATA_CONTENT_URI = Uri.parse(BASE_URI + "/data");
            Uri FETCH_CONTENT_URI = Uri.parse(BASE_URI + "/fetch");
            Uri MESSAGE_CONTENT_URI = Uri.parse(BASE_URI + "/message");
        }
     
        /**
         * 獲取數據庫表名
         *
         * @param uri
         * @return
         */
        private String getTableName(Uri uri) {
            String tableName = null;
            switch (matcher.match(uri)) {
                case CODE_DATA:
                    tableName = DB_DATA;
                    break;
                case CODE_FETCH:
                    tableName = DB_FETCH;
                    break;
                case CODE_MESSAGE:
                    tableName = DB_MESSAGE;
                    break;
                default:
                    break;
            }
            return tableName;
        }
     
        @Override
        public boolean onCreate() {
            helper = CommonOpenHelper.getInstance(getContext());
            db = helper.getWritableDatabase();
            return false;
        }
     
        @Override
        public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
            String tableName = getTableName(uri);
            if (tableName == null) {
                throw new IllegalArgumentException("非法Uri：" + uri);
            }
            Cursor cursor = db.query(tableName, projection, selection, selectionArgs, null, null, sortOrder);
            //註冊內容觀察者，觀察數據變化
            cursor.setNotificationUri(getContext().getContentResolver(), BASE_URI);
            return cursor;
        }
     
        @Override
        public String getType(Uri uri) {
            return null;
        }
     
        @Override
        public Uri insert(Uri uri, ContentValues values) {
            String tableName = getTableName(uri);
            if (tableName == null) {
                throw new IllegalArgumentException("非法Uri：" + uri);
            }
            long rowId = db.insert(tableName, null, values);
            if (rowId == -1) {
                return null;
            } else {
                //發送內容廣播
                getContext().getContentResolver().notifyChange(BASE_URI, null);
                return ContentUris.withAppendedId(uri, rowId);
            }
        }
     
        @Override
        public int delete(Uri uri, String selection, String[] selectionArgs) {
            String tableName = getTableName(uri);
            if (tableName == null) {
                throw new IllegalArgumentException("非法Uri：" + uri);
            }
            int number = db.delete(tableName, selection, selectionArgs);
            //發送內容廣播
            getContext().getContentResolver().notifyChange(BASE_URI, null);
            return number;
        }
     
        @Override
        public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
            String tableName = getTableName(uri);
            if (tableName == null) {
                throw new IllegalArgumentException("非法Uri：" + uri);
            }
            int number = db.update(tableName, values, selection, selectionArgs);
            //發送內容廣播
            getContext().getContentResolver().notifyChange(BASE_URI, null);
            return number;
        }
    }

步驟二：在各個不一樣的數據庫中的使用

Data數據庫經過名字查詢示例

    private static boolean queryDataByName(ContentResolver resolver, String tag_id) {
            Cursor cursor = resolver.query(MyDataProvider.URI.DATA_CONTENT_URI, null, "tag_id = '" + tag_id + "'", null, null);
            if (cursor.moveToFirst()) {
                return true;
            }
            return false;
        }

Fetch數據庫插入示例

    public static boolean insert(ContentResolver resolver, Fetch fetch) {
            ContentValues values = new ContentValues();
            values.put("fetch_num", fetch.getFetch_num());
            values.put("username", fetch.getUsername());
            values.put("installationId", fetch.getInstallationId());
            values.put("created", fetch.getCreated());
            values.put("date", System.currentTimeMillis());
            resolver.insert(MyDataProvider.URI.FETCH_CONTENT_URI, values);
            return true;
        }

Message數據庫查詢示例

     public static List<Message> query(ContentResolver resolver) {             List<Message> list = new ArrayList<>();             Cursor cursor = resolver.query(MyDataProvider.URI.MESSAGE_CONTENT_URI, null, null, null, null);             while (cursor.moveToNext()) {                 Message msg = new Message();                 msg.setDate(cursor.getString(cursor.getColumnIndex("date")));                 msg.setContent(cursor.getString(cursor.getColumnIndex("content")));                 msg.setId(cursor.getInt(cursor.getColumnIndex("id")));                 list.add(0, msg);             }             return list;         }