Question

为什么我们需要设定预测 Map withite QueryBuilder ? 例如,我们制定了这一哈希姆博:

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.CREATED_DATE, Notes.CREATED_DATE);
sNotesProjectionMap.put(Notes.MODIFIED_DATE, Notes.MODIFIED_DATE);

在“顺序”中,我们还具体说明了活动中的预测、选择等,因此,首先应该做的是这一 has子?

@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
        String sortOrder) {
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
    qb.setTables(NOTES_TABLE_NAME);

    switch (sUriMatcher.match(uri)) {
    case NOTES:
        qb.setProjectionMap(sNotesProjectionMap);
        break;

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

    //...
    SQLiteDatabase db = mOpenHelper.getReadableDatabase();
    Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, orderBy);

    c.setNotificationUri(getContext().getContentResolver(), uri);
    return c;
}

增编

Answer 1

http://developer.android.com/vis/android/database/sqlite/SQLite QueryBuilder.html#set ProjectionMap%28java.util.Map%3Cjava.lang.String,%20java.lang.String%3E%29”rel=“nofollow”>setprojectionmap。它从申请栏目改为数据库栏目。哈希姆将翻译。

The key in the map is the column name the application will use and the value is the column name in the database.

They are identical in the NotePadProvider in your example, but they could differ if the name of a column in the database changed and you wanted to keep the change transparent to applications using the content provider.

例如,如果数据库中列有“所有权”领域的名称(载于附注)。 TITLE改为“连续”,新的经常说明。也可以设立全国扫盲中心,在加入计划时将考虑:

sNotesProjectionMap = new HashMap<String, String>();
...
sNotesProjectionMap.put(Notes.TITLE, Notes.CONTENT);
...

友情链接