ios - Am I using correctly the requestImageForRequest at DFImageManager? -

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i'm using lib called dfimagemanager, , i'm not quite sure i'm going right way.

i led believe within completion block of requestimageforrequest info can used detect if request success.

however, 10% of time info nil image has value.

what info param for? when info nil, can still use value of image?

dfimagerequestoptions *options = [[dfimagerequestoptions alloc] init]; options.expirationage = 60;  dfimagerequest *request = [dfimagerequest requestwithresource:[nsurl urlwithstring:imageurl] targetsize:imageview.frame.size contentmode:dfimagecontentmodeaspectfill options:options];  [[dfimagemanager sharedmanager] requestimageforrequest:request completion:^(uiimage *image, nsdictionary *info) {          if (info != nil) {              [imageview setimage:image];         }         else {              // use placeholder         } }];

completion block guaranteed called on main thread. completion block called synchronously when requested image can retrieved memory cache , request made on main thread.

this case when info nil. implementation similar phimagemanager, calls completion blocks synchronously (instead of asynchronously) based on request. necessary reload ui without worrying drawing frames empty image views, when images available in memory cache. , single requestimageforrequest method keeps memory caching transparent client.

what info param for?

if holds error when there 1 (see dfimageinfoerrorkey key). , requestid (dfimageinforequestidkey). info nil, when request handled memory cache.

when info nil, can still use value of image?

yes, can. should check if image not nil instead of checking info:

if (image != nil) {     [imageview setimage:image]; } else {     // use placeholder     nserror *error = info[dfimageinfoerrorkey];     // handle specific error (if there one) }

i'm going make things more obvious nullability in next release:

  • the requestid should nonnull. info should nonnull (even when request can handled memory cache) , should contain requestid.
  • the request , resource should both nonnull.
  • image manager should raise exception when request invalid (unsupported asset).

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