ios - Expected Type in Protocol -

-



i implemented protocol in objective-c , when use own class type definition xcode tells type required.

#import <foundation/foundation.h> #import <uikit/uikit.h>  #import "lprphotocapturecamera.h"  @protocol lprphotocapturecameradelegate <nsobject>  - (void)camera:(lprphotocapturecamera *)camera finishedcapturingphoto:(uiimage *)captureduiimage;  @end

i looked in header files apples delegates , edited protocol @class lprphotocapturecamera , works.

#import <foundation/foundation.h> #import <uikit/uikit.h>  #import "lprphotocapturecamera.h"  @class lprphotocapturecamera; @protocol lprphotocapturecameradelegate <nsobject>  - (void)camera:(lprphotocapturecamera *)camera finishedcapturingphoto:(uiimage *)captureduiimage;  @end

i wonder why xcode not throw error uiimage here, have explanation this?

what happened (i guessing because did not show files) lprphotocapturecamera.h imports lprphotocapturecameradelegate.h @ top of file. have import cycle.

so example, when compiling lprphotocapturecamera.m, import lprphotocapturecamera.h, imports lprphotocapturecameradelegate.h @ top of file (before declaration of lprphotocapturecamera class). lprphotocapturecameradelegate.h imports lprphotocapturecamera.h, #import guarantees file imported once, import doesn't import anything. when gets inside declaration of lprphotocapturecameradelegate protocol, refers type lprphotocapturecamera *, doesn't understand because lprphotocapturecamera hasn't been declared yet.

in other words, although lprphotocapturecameradelegate.h imports lprphotocapturecamera.h, import doesn't import lprphotocapturecamera because have started importing (and in middle of) lprphotocapturecamera.h @ higher level.

the usual way deal when types refer each other in cycle use forward declarations. declaration of lprphotocapturecameradelegate uses pointer lprphotocapturecamera, doesn't need declaration of lprphotocapturecamera class -- needs know it's class. forward declaration @class lprphotocapturecamera do, allow no longer import lprphotocapturecamera.h in lprphotocapturecameradelegate.h. similarly, if declaration of lprphotocapturecamera uses lprphotocapturecameradelegate in type of variable, e.g. id<lprphotocapturecameradelegate> delegate, doesn't need declaration of lprphotocapturecameradelegate -- needs know it's protocol, forward declaration @protocol lprphotocapturecameradelegate do, , don't have import lprphotocapturecameradelegate.h in lprphotocapturecamera.h. usually, time need import b's header in a's header if implements b protocol or inherits b class.





wiki

Comments

Post a Comment

Popular posts from this blog

Asterisk AGI Python Script to Dialplan does not work -

-
i'm stuck project have check database of sip extension incoming caller id , dial sip extension. below receive when run script on asterisk cli. -- registered sip '9125' @ 192.168.1.102:50142 > saved useragent "zoiper rv2.8.40" peer 9125 [2017-08-22 13:53:33] notice[5095]: chan_sip.c:24558 handle_response_peerpoke: peer '9125' reachable. (17ms / 2000ms) == using sip rtp tos bits 184 == using sip rtp cos mark 5 -- executing [0112617769@from-trunk:1] answer("sip/obitrunk1-0000000d", "") in new stack > 0x1ca50d0 -- probation passed - setting rtp source address 192.168.1.98:16834 -- executing [0112617769@from-trunk:2] agi("sip/obitrunk1-0000000d", "test.py") in new stack -- launched agi script /var/lib/asterisk/agi-bin/test.py args: ['/var/lib/asterisk/agi-bin/test.py'] env line: agi_request: test.py env line: agi_channel: sip/obitrunk1-0000000d env line: agi_language: en env line: a...
Read more

python - Read npy file directly from S3 StreamingBody -

-
i have many .npy (numpy) , .json files saved in s3, need download , load these files. for json files downloading files , loading dictionary using following code: obj = s3.object(bucket, key) response = obj.get() body = response['body'].read().decode('utf-8') data = json.loads(body) that way avoid writing .json file disk , reading it. now want same .npy files, equivalent? currently downloading file, saving temp file on disk , loading np.load avoid if possible. following https://stackoverflow.com/a/28196540/3509999 : obj = s3.object(bucket, key) io.bytesio(obj.get()["body"].read()) f: # rewind file f.seek(0) arr = np.load(f) wiki
Read more

kotlin - Out-projected type in generic interface prohibits the use of metod with generic parameter -

-
i start using kotlin , defined interface this: interface aadapter<vh : recyclerview.viewholder> { fun oncreateaviewholder(parent: viewgroup): vh fun onbindaviewholder(v: vh, position: int) } and when try use on code: class klasa ( private val adapter: aadapter<*> ) { fun dosth(){ //... val vh = this.adapter.oncreateaviewholder(parent) //on below line error adapter.onbindaviewholder(v, position) //... } } i error out-projected type 'aadapter<*>' prohibits use of 'public abstract fun onbindaviewholder(v: t, position: int): unit i tied add "in" or "out" definition i'm confused. how allow it. replace aadapter<*> aadapter<recyclerview.viewholder> . class klasa ( private val adapter: aadapter<recyclerview.viewholder> ) { // ... because have declared aadapter has type parameter vh type subclass of recyclerview....
Read more