CODEWITHSUNDEEP
scopeobjective-c-blocks
ios user
ios user

Reputation: 11

block function in ios

hello everyone I am new to IOS developement and I am working of block functions.I am confused about their working.My question is can we print the block function's parameters to outside its block. My code is like

[messageRenderingOperation start:^(NSString * plainTextBodyString, NSError * error) {
        NSLog(@"plain text:%@",plainTextBodyString);
      }];
NSLog(@"plain text body:%@",plainTextBodyString);

My output ids as follows:-

plain text:hello world
plain text body:(null)

why this value is null. Please help me.

Upvotes: 0

Views: 100

Answers (1)

Vaibhav
Vaibhav

Reputation: 335

declare one variable outside block

__block NSString *plainTextString;

[messageRenderingOperation start:^(NSString * plainTextBodyString, NSError * error) {
        //assign value
        plainTextString =plainTextBodyString;
        NSLog(@"plain text:%@",plainTextBodyString);
      }];

//now you can access variable
NSLog(@"plain text body:%@",plainTextString);

or,

 __block NSString *plainTextString; 
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
    [messageRenderingOperation start:^(NSString * plainTextBodyString, NSError * error) { 
     //assign value 
    plainTextString =plainTextBodyString; 
    NSLog(@"plain text:%@",plainTextBodyString); 
dispatch_semaphore_signal(semaphore); }]; 
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER); 
//now you can access variable 
    NSLog(@"plain text body:%@",plainTextString);

Please refer this tutorial for more details https://developer.apple.com/library/mac/documentation/cocoa/conceptual/ProgrammingWithObjectiveC/WorkingwithBlocks/WorkingwithBlocks.html

Upvotes: 1

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