存储方式之ContentProvider

开始学习之前先回忆一下android的几种存储方式：

1. SharedPreference   
2. ContentProvider
3. SQLite数据库
4. 文件存储
5. sdCard存储

这几种是我记忆中的5中存储方式。最喜欢的也是用的最多的是SharedPreference简单方便。然后就是数据库，因为用的多，不得不喜欢呀。一直让我很纠结的就是今天学习的ContentProvider。原因？因为用的少呀（其实是没用过）。因为项目里不需要用，也就只是了解一下，没有去研究过，今天又时间，学习了一下，赶紧记录下来，好记性不如烂笔头呀！

　　ContentProvider的几个要点：

1. 定义基本字段
2. 在manifest里添加（provider和在需要用的activity里添加两个新的minetype）
3. 继承ContentProvider

下面是代码：

　　1.定义基本字段

public class NotePad {
    public static final String AUTHORITY = "com.google.provider.NotePad";    //ContentProvider的uri

    public NotePad(){}
    
    //定义基本字段
    public static final class Notes implements BaseColumns{
        public Notes(){}
        //这里notes跟数据库里表名相同（我是这么认为的，不知道可不可以不一样，回头改改试试看）
        public static final Uri CONTENT_URI    = Uri.parse("content://" + AUTHORITY + "/notes");
        
        //新的MIME类型-多个
        public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.google.note";
        
        // 新的MIME类型-单个
        public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.google.note";
        
        public static final String    DEFAULT_SORT_ORDER    = "modified DESC";
        
        //字段
        public static final String    TITLE                = "title";
        public static final String    NOTE                = "note";
        public static final String    CREATEDDATE            = "created";
        public static final String    MODIFIEDDATE        = "modified";
    }
}

　　2.在manifest里添加（provider和在需要用的activity里添加两个新的minetype）

<activity
            android:label="@string/app_name"
            android:name="contentPro.DataProviderActivity" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
            <intent-filter>
                <data android:mimeType="vnd.android.cursor.dir/vnd.google.note"/>
            </intent-filter>
            <intent-filter>
                <data android:mimeType="vnd.android.cursor.item/vnd.google.note"/>
            </intent-filter>
        </activity>
        
       
   <provider android:name="contentPro.NotePadProvider" android:authorities="com.google.provider.NotePad"/>

　

　3.继承ContentProvider

public class NotePadProvider extends ContentProvider {
    private static final String TAG = "NotePadProvider";
    // 数据库名
    private static final String DATABASE_NAME = "note_pad.db";
    private static final int DATABASE_VERSION = 2;
    // 表名
    private static final String NOTES_TABLE_NAME = "notes";
    private static HashMap<String, String> sNotesProjectionMap;
    private static final int NOTES = 1;
    private static final int NOTE_ID = 2;
    private static final UriMatcher sUriMatcher;
    private DatabaseHelper mOpenHelper;
    // 创建表SQL语句
    private static final String CREATE_TABLE = "CREATE TABLE "
            + NOTES_TABLE_NAME + " (" + Notes._ID + " INTEGER PRIMARY KEY,"
            + Notes.TITLE + " TEXT," + Notes.NOTE + " TEXT,"
            + Notes.CREATEDDATE + " INTEGER," + Notes.MODIFIEDDATE + " INTEGER"
            + ");";

    static {
        sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        sUriMatcher.addURI(NotePad.AUTHORITY, "notes", NOTES);
        sUriMatcher.addURI(NotePad.AUTHORITY, "notes/#", NOTE_ID);

        sNotesProjectionMap = new HashMap<String, String>();
        sNotesProjectionMap.put(Notes._ID, Notes._ID);
        sNotesProjectionMap.put(Notes.TITLE, Notes.TITLE);
        sNotesProjectionMap.put(Notes.NOTE, Notes.NOTE);
        sNotesProjectionMap.put(Notes.CREATEDDATE, Notes.CREATEDDATE);
        sNotesProjectionMap.put(Notes.MODIFIEDDATE, Notes.MODIFIEDDATE);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper {
        // 构造函数-创建数据库
        DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        // 创建表
        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(CREATE_TABLE);
        }

        // 更新数据库
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            db.execSQL("DROP TABLE IF EXISTS notes");
            onCreate(db);
        }
    }

    @Override
    public boolean onCreate() {
        mOpenHelper = new DatabaseHelper(getContext());
        return true;
    }

    @Override
    // 查询操作
    public Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder) {
        SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
        switch (sUriMatcher.match(uri)) {
        case NOTES:
            qb.setTables(NOTES_TABLE_NAME);
            qb.setProjectionMap(sNotesProjectionMap);
            break;

        case NOTE_ID:
            qb.setTables(NOTES_TABLE_NAME);
            qb.setProjectionMap(sNotesProjectionMap);
            qb.appendWhere(Notes._ID + "=" + uri.getPathSegments().get(1));
            break;

        default:
            throw new IllegalArgumentException("Unknown URI " + uri);
        }
        String orderBy;
        if (TextUtils.isEmpty(sortOrder)) {
            orderBy = NotePad.Notes.DEFAULT_SORT_ORDER;
        } else {
            orderBy = sortOrder;
        }
        SQLiteDatabase db = mOpenHelper.getReadableDatabase();
        Cursor c = qb.query(db, projection, selection, selectionArgs, null,
                null, orderBy);
        c.setNotificationUri(getContext().getContentResolver(), uri);
        return c;
    }

    @Override
    // 如果有自定义类型，必须实现该方法
    public String getType(Uri uri) {
        switch (sUriMatcher.match(uri)) {
        case NOTES:
            return Notes.CONTENT_TYPE;

        case NOTE_ID:
            return Notes.CONTENT_ITEM_TYPE;

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

    @Override
    // 插入数据库
    public Uri insert(Uri uri, ContentValues initialValues) {
        if (sUriMatcher.match(uri) != NOTES) {
            throw new IllegalArgumentException("Unknown URI " + uri);
        }
        ContentValues values;
        if (initialValues != null) {
            values = new ContentValues(initialValues);
        } else {
            values = new ContentValues();
        }
        Long now = Long.valueOf(System.currentTimeMillis());

        if (values.containsKey(NotePad.Notes.CREATEDDATE) == false) {
            values.put(NotePad.Notes.CREATEDDATE, now);
        }
        if (values.containsKey(NotePad.Notes.MODIFIEDDATE) == false) {
            values.put(NotePad.Notes.MODIFIEDDATE, now);
        }
        if (values.containsKey(NotePad.Notes.TITLE) == false) {
            Resources r = Resources.getSystem();
            values.put(NotePad.Notes.TITLE,
                    r.getString(android.R.string.untitled));
        }
        if (values.containsKey(NotePad.Notes.NOTE) == false) {
            values.put(NotePad.Notes.NOTE, "");
        }
        SQLiteDatabase db = mOpenHelper.getWritableDatabase();
        long rowId = db.insert(NOTES_TABLE_NAME, Notes.NOTE, values);
        if (rowId > 0) {
            Uri noteUri = ContentUris.withAppendedId(NotePad.Notes.CONTENT_URI,
                    rowId);
            getContext().getContentResolver().notifyChange(noteUri, null);
            return noteUri;
        }
        throw new SQLException("Failed to insert row into " + uri);
    }

    @Override
    // 删除数据
    public int delete(Uri uri, String where, String[] whereArgs) {
        SQLiteDatabase db = mOpenHelper.getWritableDatabase();
        int count;
        switch (sUriMatcher.match(uri)) {
        case NOTES:
            count = db.delete(NOTES_TABLE_NAME, where, whereArgs);
            break;

        case NOTE_ID:
            String noteId = uri.getPathSegments().get(1);
            count = db.delete(NOTES_TABLE_NAME,
                    Notes._ID
                            + "="
                            + noteId
                            + (!TextUtils.isEmpty(where) ? " AND (" + where
                                    + ')' : ""), whereArgs);
            break;

        default:
            throw new IllegalArgumentException("Unknown URI " + uri);
        }
        getContext().getContentResolver().notifyChange(uri, null);
        return count;
    }

    @Override
    // 更新数据
    public int update(Uri uri, ContentValues values, String where,
            String[] whereArgs) {
        SQLiteDatabase db = mOpenHelper.getWritableDatabase();
        int count;
        switch (sUriMatcher.match(uri)) {
        case NOTES:
            count = db.update(NOTES_TABLE_NAME, values, where, whereArgs);
            break;

        case NOTE_ID:
            String noteId = uri.getPathSegments().get(1);
            count = db.update(NOTES_TABLE_NAME, values,
                    Notes._ID
                            + "="
                            + noteId
                            + (!TextUtils.isEmpty(where) ? " AND (" + where
                                    + ')' : ""), whereArgs);
            break;

        default:
            throw new IllegalArgumentException("Unknown URI " + uri);
        }
        getContext().getContentResolver().notifyChange(uri, null);
        return count;
    }
}

 4.应用

public class DataProviderActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        //插入数据
        ContentValues values = new ContentValues();
        values.put(NotePad.Notes.TITLE, "title1");
        values.put(NotePad.Notes.NOTE, "NoteNote1");
        getContentResolver().insert(NotePad.Notes.CONTENT_URI, values);
        
        values.clear();
        values.put(NotePad.Notes.TITLE, "title2");
        values.put(NotePad.Notes.NOTE, "NoteNote2");
        getContentResolver().insert(NotePad.Notes.CONTENT_URI, values);
        
        /* 显示 */
        displayNote();
    }

    private void displayNote() {
        // TODO Auto-generated method stub
        String columns[] = new String[]{
                NotePad.Notes._ID,
                NotePad.Notes.TITLE, 
                NotePad.Notes.NOTE, 
                NotePad.Notes.CREATEDDATE, 
                NotePad.Notes.MODIFIEDDATE
        };
        Uri myUri = NotePad.Notes.CONTENT_URI;
        Cursor cursor = this.managedQuery(myUri, columns, null, null, null);
        if (cursor.moveToFirst()) {
            String id = null;
            String title = null;
            
            do{
                id = cursor.getString(cursor.getColumnIndex(NotePad.Notes._ID));
                title = cursor.getString(cursor.getColumnIndex(NotePad.Notes.TITLE));
                Toast toast=Toast.makeText(this, "TITLE："+id + "NOTE：" + title, Toast.LENGTH_LONG);
                toast.setGravity(Gravity.TOP|Gravity.CENTER, 0, 40);
                toast.show();
            }while(cursor.moveToNext());
        }
    }
}

以上代码来源：http://blog.csdn.net/yinyuan1987/article/details/6973074

感谢yinyuan1987 代码很易懂！