c++ - QModelIndex becomes invalid when removing rows -

-

i'm subclassing qabstractitemmodel display items in qtreeview, , within subclass (projectmodel), have function delete currently-selected index in tree view. component class used represent members of model:

void projectmodel::deletecomponent() {     qmodelindex child_index = _treeview->selectionmodel()->currentindex();     component* child = static_cast<component*>(child_index.internalpointer());      component* parent = child->parent();     qmodelindex parent_index = createindex(parent->row(), 0, parent);      int row = child->row();      beginremoverows(parent_index, row, row);     parent->delete_child(child);     endremoverows(); }

the parent , child indicies , raw pointers before call beginremoverows; debugger shows point correct item , parent. however, program crashes after calling beginremoverows. specifically, crashes in projectmodel::parent():

qmodelindex projectmodel::parent(const qmodelindex &index) const {         if (!index.isvalid())         return qmodelindex();      component* item = getitem(index);        //fails cast index internal pointer valid component*     component* parentitem = item->parent();      if (parentitem == _rootnode)         return qmodelindex();      return createindex(parentitem->row(), 0, parentitem); }

when break on crash , examine debugger output, shows variable item in parent() function garbage. somehow looks qmodelindex gets corrupted between call deletecomponent , call parent. there blatantly wrong i'm doing, or problem perhaps more subtle?

this expected.

non-persistent indices valid until change structure of model. structural change change signaled other emitting datachanged.

structural changes must considered barriers index lifetime: must discard non-persistent indices held before structural change.

depending on deletecomponent called, happens caller holds indices, deletecomponent invalidates them all, , you're in undefined behavior territory there onwards.

you need use persistent indices if want them stay valid on structural changes, , they'll valid if given item still exists. if you're using own model, need explicitly support persistent indices, , users of model must use them.


Comments

Post a Comment

Popular posts from this blog

Fail to load namespace Spring Security http://www.springframework.org/security/tags -

-
i have problem namespace of spring security on xhtml page. don't understand why can't load uri, , have following issue: whitelabel error page application has no explicit mapping /error, seeing fallback. tue jul 21 16:58:12 utc 2015 there unexpected error (type=not found, status=404). please need help! possible uri has been changed? best regards you using incorrect namespace url. correct url http://www.springframework.org/schema/security the error page seeing spring source website since not recognize url. try visiting http://www.springsource.org/security/tags in browser update : spring security tags used in jsp page correct tag lib declaration is: <%@ taglib prefix="sec" uri="http://www.springframework.org/security/tags" %>
Read more

sql - MySQL query optimization using coalesce -

-
can explain me why second query faster first? (first 1 takes around 40 seconds, second 1 less 0.1) select releases.feature_code, releases.platform_id, version, release_date, general_available, uri, filesize, display_name, feature_name.full_name, if ((select exists(select 1 release_exceptions releases.feature_code = release_exceptions.feature_code , releases.platform_id = release_exceptions.platform_id , releases.version = release_exceptions.version) = 1), 1, 0) release_exceptions releases left outer join platform using(platform_id) left outer join feature_name using(feature_code) order version desc; ~~~ query 2 ------------------ ~~~ select feature_code, version, release_date, general_available, platform_id, uri, filesize, display_name, feature_name.full_name, coalesce(release_exceptions, 0) release_exceptions mus.releases left outer join ( select distinct feature_code, version, platform_id, 1 release_exceptions mus.release_exceptions ) release_exceptions using ...
Read more

unity3d - Unity local avoidance in user created world -

-
i'm using unity3d networked multiplayer online game have large complex 3d terrain scene forest, trees, cliff, hills, mountains, bounders, etc. players can build structures sort of minecraft, , put them anywhere in scene, or move them around anytime. aside human controlled players, there automated ai players , objects animals roaming around scene following path. the problem how make these automated ai players , animals, able navigate around static , dynamic player created structures, because path follow can blocked player created structures, or other players , other ai objects, cliffs etc. have find away around them or on track if tumble down off high cliff example. so made navmesh , used navagents, takes care of static, non moving objects, how make ai players navigate around each other , dynamic structures created players can number in hundreds? i thought of adding navmeshobstacle everything, result in being attached hundreds of objects since user created structures b...
Read more