objective c - How is it better to wait an asynchronous method to be finished in iPhone app? -

everybody. want understand, how shoud procceed situations when asynchronous method has "didfinish:@selector(sel)" parameter. code example is:

// // authentication check - ( void )authenticationsuccess: ( gdataserviceticket* ) ticket          authenticatedwitherror: ( nserror* ) error {      if ( error == nil )     {         nslog( @"authentication success" );     }     else      {         nslog( @"authentication error" );     } } //  - ( void ) fetchfeedofspreadsheets {      //create , authenticate google spreadsheet service      if ( !(mservice) )     {         gdataservicegooglespreadsheet *service = [self spreadsheetservice];         [mservice autorelease];         mservice = [service retain];         }      // check autentication success ( invoke "authenticationsuccess" method debug success & error )     [mservice authenticatewithdelegate: self                didauthenticateselector:@selector(authenticationsuccess:                                                  authenticatedwitherror:) ];       // here want make pause , whait result, either authenticated or not     // , make "if" statement contintue working on server, or return error       //fetch retrieves feed of spreadsheets entries      nsurl *feedurl = [ nsurl urlwithstring: kgdatagooglespreadsheetsprivatefullfeed ];     gdataserviceticket *ticket;     ticket = [mservice fetchfeedwithurl: feedurl                                delegate: self                       didfinishselector: @selector(spreadsheetsticket:finishedwithfeed:                                                    error: ) ];      // here want wait second time. want "spreadsheetsticket:             // finishedwithfeed:error:" procceed error , put feed in nsarray object     // , after want work nsarray right here } 

i's clear, can push code want end of "authenticationsuccess" method section, it's clear, it's wrong way solve proble. there number of situations this, call asynchronous method selector parameter, , want find solution providing me flexible code writing.

thanks in advance.

it's standard practice in objective-c put code executed after authentication in authenticationsucess: method. might not it, life.

many people had same complaint you, on ios 4 , later, there's called blocks allow write code executed after authentication in method initiates authentication, in

[mservice authenticateandexecute:^{                   code executed when authenticated ;           }            whenerror:^{                  code executed when authentication failed;           } ];  

but in case need modify api, possible using categories. see this blog post mike ash. has many other posts on blocks on same blog, instructive.