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A light-weighted Promise library for Objective-C

About Promise

The Promise object is used for deferred and asynchronous computations. A Promise represents an operation that hasn't completed yet, but is expected in the future. Ref

In JavaScript, Promise handles asynchronising call beatifully:

getJSON("/posts.json").then(function(posts) {
  // ...
}).catch(function(error) {
  console.log('something wrong!', error);

Usage of RWPromiseKit

Here is a basic example:

RWPromise* p1 = [RWPromise promise:^(ResolveHandler resolve, RejectHandler reject) {
p1.then(^id(NSString* value){
  NSLog(@"%@",value); //result
  return @"resultOfThen";
}).then(^id(NSString* value){
  NSLog(@"%@",value); //resultOfThen
  NSException *e = [NSException exceptionWithName:@"name"
  @throw e;
  return nil;
}).catch(^(NSError* error){
  NSLog(@"%@",[error description]); //error contains exception

Using RWPromise is exactly same as using promise in js. resolve and reject are provided in initial block as input parameters, these two methods are used to change the state of a promise. Block passed in then will be invoked when a promise is set to resolved while one in catch will be invoked when rejected.

For more infomation about the API of promise in js, please reference here

Suppoted API


  • then
  • catch
  • finally
  • after
  • retry
  • timeout
  • map
  • filter
  • reduce
  • race
  • all
  • resolve
  • reject


  • progress


  • Cocoapods
pod 'RWPromiseKit', '0.2.0'
  • Source code

Copy all source files from directory Class to your project

Issues and Todo list

  • I simplify the usage of then compared with js. Just pass only one handler block to handle when last promise is resolved. To reject, you can raise an expection or return a new promise.

  • some other API: map,filter,reduce

  • Integrate with 3rd party lib

  • Unit test are not finished

  • Complicated test cases.

  • Doc with more detail


Licensed under MIT. Full license here »