【Android ContentProvider 一】关于ContactsContract.CommonDataKinds.Phone.CONTENT_URI的一点理解

一切都要从ContactsContract.CommonDataKinds.Phone.CONTENT_URI说起。
前两天在学习Google官方培训课程中的《Android联系人信息与位置信息》部分时，始终没有理解到getActivity().getContentResolver().query(Uri uri,
String[] projection, String selection,String[] selectionArgs, String sortOrder)方法中uri这个参数的使用，当时很傻逼的认为搜索电话号码不就是将uri赋值为ContactsContract.Contacts.CONTENT_URI搜索，结果发现Contacts中只有一个HAS_PHONE_NUMBER参数，之后搜索发现URI有很多种，比如

• ContactsContract.CommonDataKinds.Phone.CONTENT_URI
• ContactsContract.Data.CONTENT_URI
• ContactsContract.RawContacts.CONTENT_URI

因为对uri参数不熟悉的原因，同时发现ContactsContract联想出来的类很多，参数也很多，然后开始各种胡乱尝试uri，比如ContactsContract.CommonDataKinds.Phone.NUMBER，结果不出所料的程序开始疯狂崩溃。。。
然后我开始重新学习了下联系人数据库contacts2.db、ContentResolver.query()中uri、uri等于ContactsContract.CommonDataKinds.Phone.CONTENT_URI时，ContactsProvider是怎样工作的。

先了解到关于联系人数据库重要的有以下几个表：
1. contacts
2. raw_contacts
3. data
4. mimetypes

当把getContentResolver().query()方法中的uri参数赋值为ContactsContract.CommonDataKinds.Phone.CONTENT_URI查找联系人数据时，实际上是在对data表进行查找。直接从ContactsProvider接口中ContactsProvider2类的query()方法看起。
随着query()方法一步步往下走：

ContactsProvider2.java

    @Override    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,            String sortOrder) {        //第一步：直接return query()        return query(uri, projection, selection, selectionArgs, sortOrder, null);    }    @Override    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,            String sortOrder, CancellationSignal cancellationSignal) {        if (mapsToProfileDb(uri)) {            switchToProfileMode();            //第二步：return mProfileProvider.query()            return mProfileProvider.query(uri, projection, selection, selectionArgs, sortOrder,                    cancellationSignal);        }}    @Override    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,            String sortOrder, CancellationSignal cancellationSignal) {        incrementStats(mQueryStats);        try {        //第三步:mDelegate.queryLocal(),这个方法就是关键了            return mDelegate.queryLocal(uri, projection, selection, selectionArgs, sortOrder, -1,                    cancellationSignal);        } finally {            finishOperation();        }    }

queryLocal()方法中根据sUriMatcher.match()所返回的code值，在switch语句中进行了匹配处理工作，而在开始的时候sUriMatcher有addURI，所以可以知道ContactsContract.CommonDataKinds.Phone.CONTENT_URI对应的code就是PHONES
ContactsProvider2.java

static {    // Contacts URI matching table    final UriMatcher matcher = sUriMatcher;    matcher.addURI(ContactsContract.AUTHORITY, "data", DATA);    matcher.addURI(ContactsContract.AUTHORITY, "data/#", DATA_ID);    matcher.addURI(ContactsContract.AUTHORITY, "data/phones", PHONES);    matcher.addURI(ContactsContract.AUTHORITY, "data_enterprise/phones", PHONES_ENTERPRISE);    matcher.addURI(ContactsContract.AUTHORITY, "data/phones/#", PHONES_ID);    matcher.addURI(ContactsContract.AUTHORITY, "data/phones/filter", PHONES_FILTER);}

所以在queryLocal()方法中进入case PHONES:
ContactsProvider2.java

final int match = sUriMatcher.match(uri);switch(match){    //此处省略......    case PHONES:        //在mimetypes表中找Phone的MIME类型ID值        final String mimeTypeIsPhoneExpression =                DataColumns.MIMETYPE_ID + "=" + mDbHelper.get().getMimeTypeIdForPhone();        final String mimeTypeIsSipExpression =                DataColumns.MIMETYPE_ID + "=" + mDbHelper.get().getMimeTypeIdForSip();        setTablesAndProjectionMapForData(qb, uri, projection, false);        if (match == CALLABLES) {            qb.appendWhere(" AND ((" + mimeTypeIsPhoneExpression +                    ") OR (" + mimeTypeIsSipExpression + "))");        } else {            //match=PHONES，将 _id = 1作为查询条件添加到where语句中            qb.appendWhere(" AND " + mimeTypeIsPhoneExpression);        }        final boolean removeDuplicates = readBooleanQueryParameter(                uri, ContactsContract.REMOVE_DUPLICATE_ENTRIES, false);        if (removeDuplicates) {            groupBy = RawContacts.CONTACT_ID + ", " + Data.DATA1;            addressBookIndexerCountExpression = "DISTINCT "                    + RawContacts.CONTACT_ID + "||','||" + Data.DATA1;        }        break;    }    qb.setStrict(true);    // Auto-rewrite SORT_KEY_{PRIMARY, ALTERNATIVE} sort orders.    String localizedSortOrder = getLocalizedSortOrder(sortOrder);    Cursor cursor =            doQuery(db, qb, projection, selection, selectionArgs, localizedSortOrder, groupBy,                    having, limit, cancellationSignal);    if (readBooleanQueryParameter(uri, Contacts.EXTRA_ADDRESS_BOOK_INDEX, false)) {        bundleFastScrollingIndexExtras(cursor, uri, db, qb, selection,                selectionArgs, sortOrder, addressBookIndexerCountExpression,                cancellationSignal);    }    if (snippetDeferred) {        cursor = addDeferredSnippetingExtra(cursor);    }    return cursor;}

通过getMimeTypeIdForPhone()方法在mimetypes表中根据vnd.android.cursor.item/phone_v2类型来找到Phone对应的_ID，添加到查找的where语句中，最后返回一个cusor

总结：

当使用ContactsContract.CommonDataKinds.Phone.CONTENT_URI作为uri的参数查找联系人时，实际上默认查找条件已经变成了在data表中mimetype_id = 1(即类型为vnd.android.cursor.item/phone_v2)的结果集里面查找。这时候再在query()方法里添加自己自定义的projection、selection、selectionArgs，就能在电话号码结果集中搜索到自己想要的结果了。