ios - How to ensure remotely-fetched images in UITableView cells always filled? -


i have gotten question several times in job interviews: have uitableview , user scrolling fast. how make sure @ of cells' images being loaded server visible wherever user scrolls to.

i can think of several techniques. instance have done use operation queue, loaded requests fetch images, , when user starts scrolling, empty queue , fill requests images wherever user going towards.

another solution fill images super-low-resolution thumbnails e.g. 4-point gradient image, albeit bad one, there long before real image arrives.

i key here "wherever user scrolls to". because of that, shouldn't start downloading images until know cells going visible.

so watch uiscrollviewdelegate call:

- (void)scrollviewdidenddecelerating:(uiscrollview *)scrollview

at point, cells visible using:

- (nsarray *)indexpathsforvisiblerows

and spin off downloads images. putting together:

- (void)scrollviewdidenddecelerating:(uiscrollview *)scrollview {     nsarray *theindexpaths = [self.tableview indexpathsforvisiblerows];     (nsindexpath *theindexpath in theindexpaths) {         someobject *myobject = self.listofmyobjects[theindexpath.row];         [myobject downloadimage];     } }

this basic. need update cell, etc.


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