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Thread: MVC - canFetchMore() is not working as expected

  1. #1
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    Default MVC - canFetchMore() is not working as expected

    I have implemented customized model for lazily loading data, so I have reimplemented canfetchMore() & fetchMore().

    - they are working fine for root item, when i scroll down these functions are getting called and I am loading data & population it.
    - But in case of child's its not working as expected (may be my understanding is wrong). I have many rows (more than million) child's for the top level items, so I decided to load them also on demand or lazily. but canFetchMore() is calling only one time when I expand the item (when I expand the item i am reading top 100 immediate child's and inserting them, so that entire view is full with these child's & then when I scroll down my expectation is canFetchMore() should be called with parent as that child to which i inserted 100 child's but once i insert 100/some items into that item canFetchMore() is not calling until I collapse & expand it again.)
    because of this I am not able to fetch more/remaining child's & insert them.

    In one line: canfetchMore() is calling only when expand the item, Its not getting called when I expand & insert few items and then scroll down.

    Is this bug ? or Can i manage this in some other way. ???
    Thanks :-)

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    Default Re: MVC - canFetchMore() is not working as expected

    It's a bug that ended up being a feature. It is theoretically possible to use the model the way you want (which seems reasonable) but Qt's QTreeView implementation does not offer such functionality.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

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    Default Re: MVC - canFetchMore() is not working as expected

    Quote Originally Posted by prasad_N View Post
    It's a bug that ended up being a feature..
    Strange feature, did somebody report this bug already ? (or can i report this as bug ?).

    Quote Originally Posted by prasad_N View Post
    It is theoretically possible to use the model the way you want
    Could you please let me know one way (more if possible :-) ) to handle this situation.
    Last edited by prasad_N; 9th October 2015 at 08:16.
    Thanks :-)

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    Default Re: MVC - canFetchMore() is not working as expected

    I tried to get the last element with the help of view geometry while scrolling, But It did not work at all.

    Qt Code:
    1. scroolingDown(int val)
    2. {
    3. QModelIndex index = itemAt(rect().bottomLeft());
    4. }
    To copy to clipboard, switch view to plain text mode 


    any other suggestions/way to achieve this ??
    Thanks :-)

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    Default Re: MVC - canFetchMore() is not working as expected

    Any help or suggestions from Qt experts please ??
    Thanks :-)

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    Default Re: MVC - canFetchMore() is not working as expected

    I did in the way I am not supposed to do.

    in data() function I am checking If it is last child Of a valid parent item(non root item) & This parent still have some items than I am fetching some more data and inserting.

    I know this is the stupid way as I am fetching & inserting data in data() function & I should not do it here, But did this at this point of of time nothing flashes in my mind.
    May be I need to go through QTreeView source code to get some pointers to work on this feature.
    Thanks :-)

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    Default Re: MVC - canFetchMore() is not working as expected

    Quote Originally Posted by prasad_N View Post
    Strange feature, did somebody report this bug already ? (or can i report this as bug ?).
    Feel free to do that.

    Could you please let me know one way (more if possible :-) ) to handle this situation.
    You would have to reimplement the view to do it properly. You have to detect a situation where the view is scrolled to a point where the last populated item is visible on a certain level and then ask the model to update itself.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

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