ContentProvider（一）

注册ContentProvider:

<provider
    android:name=".provider.UserProvider"
    android:authorities="com.rw.contentprovider.provider.UserProvider"
    android:exported="true"
    ></provider>

其中authorities是URI中的域名部分，可以随便取，但必须在整个系统中唯一

      name和ACtivity一样，告诉虚拟机与之绑定的class

       exported指定ContentProvider是否允许被其他应用调用

继承ContentProvider的以下5个方法：

可以根据自己的业务需求，实现相应的方法

以下是自己写的demo，有之前写的DBOpenHelper类的支持

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

        SQLiteDatabase dataBase= this.userDatabase.getReadableDatabase();
        switch (USERMATCHER.match(uri)) {
        case USER:
            long rawId= ContentUris.parseId(uri);
            String where="uid="+rawId;
            if(selection!=null){
                where+=" and "+selection;
            }
            return dataBase.query("users", projection, where, selectionArgs, null, null,sortOrder);

        case USERS:
            return dataBase.query("users", projection, selection, selectionArgs, null,null, sortOrder);
        default:
            throw new IllegalArgumentException("this unknown Uri:"+uri.toString());

        }
    }

public String getType(Uri uri) {
        switch (USERMATCHER.match(uri)) {
        case USER:
            return "vnd.android.cursor.dir/user";
        case USERS:
            return "vnd.android.cursor.item/user";    

        default:

            throw new IllegalArgumentException("this is unknown Uri:"+uri.toString());
        }
    }

public Uri insert(Uri uri, ContentValues values) {
        SQLiteDatabase dataBase= this.userDatabase.getWritableDatabase();
        switch (USERMATCHER.match(uri)) {
        case USER:

            throw new IllegalArgumentException("this Uri can not insert a record to Content!");

        case USERS:
            long rawId=dataBase.insert("users", null, values);

            return ContentUris.withAppendedId(uri, rawId);
        default:

            throw new IllegalArgumentException("this unknown Uri:"+uri.toString());
        }
    }

public int delete(Uri uri, String selection, String[] selectionArgs) {
        SQLiteDatabase dataBase= this.userDatabase.getWritableDatabase();
        switch (USERMATCHER.match(uri)) {
        case USER:
            long rawId= ContentUris.parseId(uri);
            String where="uid="+rawId;
            if(selection!=null){
                where+=" and "+selection;
            }
            return dataBase.delete("users", where, selectionArgs);
        case USERS:

            return dataBase.delete("users", selection, selectionArgs);
        default:

            throw new IllegalArgumentException("this unknown Uri:"+uri.toString());
        }
    }

public int update(Uri uri, ContentValues values, String selection,
            String[] selectionArgs) {
        SQLiteDatabase dataBase=userDatabase.getWritableDatabase();
        switch (USERMATCHER.match(uri)) {
        case USER:
            long rawId= ContentUris.parseId(uri);
            String where="uid="+rawId;
            if(selection!=null){
                where+=" and "+selection;
            }
            return dataBase.update("users", values, where, selectionArgs);
        case USERS:
            if(selection!=null){
                return dataBase.update("users", values, selection, selectionArgs);
            }else{
                throw new IllegalArgumentException("this Uri con not update record from dataBase");
            }
        default:

            throw new IllegalArgumentException("this Uri is unknown:"+uri.toString());
        }
    }

在使用者使用ContentResolver对数据进行CURD操作时,分别调用了与之对应的的方法，其实其底层也是根据URI获取到了这个ContentProvider,进而将参数传递给ContentProvider中与之对应的方法。以下是其中一类的Code

public final int update(Uri uri, ContentValues values, String where,
            String[] selectionArgs) {        //在这里根据传入的Uri，获取到一个ContentProvider
        IContentProvider provider = acquireProvider(uri);
        if (provider == null) {
            throw new IllegalArgumentException("Unknown URI " + uri);
        }
        try {
            long startTime = SystemClock.uptimeMillis();            //在这里真正执行ContentProvider的update方法
            int rowsUpdated = provider.update(mPackageName, uri, values, where, selectionArgs);
            long durationMillis = SystemClock.uptimeMillis() - startTime;
            maybeLogUpdateToEventLog(durationMillis, uri, "update", where);
            return rowsUpdated;
        } catch (RemoteException e) {
            // Arbitrary and not worth documenting, as Activity
            // Manager will kill this process shortly anyway.
            return -1;
        } finally {
            releaseProvider(provider);
        }
    }