1. Jeffrey Bakker
  2. Cocoatainer




Welcome to the Cocoatainer project. This project is aimed at providing Objective-C (and Swift) developers with an iOS framework for Dependency Injection / Inversion of Control.

Cocoatainer provides an IoC container using constructor injection (as opposed to property injection) and does not require your classes to be written in an esoteric way for its dependencies to be injected. Cocoatainer supports registering components either by abstract (protocol) or by concrete type (class). The container supports the following features:

  • Adding components by pre-allocated instance
  • Adding components by block (closure) with dependencies
  • Multiple dependencies per component, auto-resolving when needed
  • Nesting of dependencies, auto-resolving when needed
  • Nesting of containers (with auto-resolving dependencies from parent)
  • Startable (with option of auto-resolution of objects not referenced outside the container, i.e. object lives solely in the container)
  • Error checking on registration (throws), to help prevent logical errors after resolution
  • API docs via XCode Quick Help tab

The Cocoatainer framework code is covered by several dozen unit tests around the above scenarios. The workspace also contains examples projects for using it from Swift and for using with Interface Builder demonstrating how to insert view objects into the container.

CocoaMug Example

If you wanted some hot cocoa, first you'd need some sort of mug to put it in, get hot water from somewhere, and of course some mixture, which may also contain toppings. You might not know specifically how or where to get these things, but you know what it takes to make hot cocoa. Maybe it would play out like this.

    CCTCocoatainer* config = [[CCTCocoatainer alloc] init];

    [config registerComponent:@protocol(HotWaterSource)
                 withInstance:[[Kettle alloc] init]];

    [config registerComponent:@protocol(Topping)
                 withInstance:[[Marshmallow alloc] init]];

    [config registerComponent:@protocol(Mix)
     ^(id<Topping> topping){
         return [[CocoaPowder alloc] initWithTopping:topping];

    [config registerComponent:@protocol(LiquidVessel)
     ^(id<HotWaterSource> source, id<Mix> mix){
         return [[CocoaMug alloc] initWithHotWater:source andMixture:mix];

    [config start:YES]; // Yes for auto-resolve when starting

The above might happen inside of some cocoa configuration module, and the below could be happening in some client code.

    id<LiquidVessel> myMug =
        [config resolveComponent:@protocol(LiquidVessel)];

    // Pass myMug to a CocoaDrinker


    // Later on inside of CocoaDrinker

    [myMug drink:20];
    [myMug checkAmount];
    [myMug drink:30];
    [myMug checkAmount];

When the above code is run, its output is like so

// The following messages are printed from objects implementing
// CCTStartable start when start is called on the container.
Boiling water to 100 degrees C.
Creating CocoaPowder mix with Marshmallow topping
Shovel three tablespoons of mixture.
Pouring a cup of hot water.
Mug is filled to 250 ml of hot Cocoa.

// These messages are printed explicitly by call
Drinking 20 ml from the mug
There is 230 ml of cocoa left in the mug
Drinking 30 ml from the mug
There is 200 ml of cocoa left in the mug

// The following dealloc print messages are triggered
// when the container is cleaned after leaving scope
// of an autoreleasepool
Someone left this 200 ml full mug here. I will just pour it out.
This cocoa powder has coagulated at the bottom.
This marshmallow is so soggy that it has nearly turned into liquid.
This water got cold and looks old. I will dump it out.

// Printed after autoreleasepool, before end of scope
Before method's local scope end.

Examples By the Block

To create a Cocoatainer container

#import "CCTCocoatainer.h"

    CCTCocoatainer* config = [[CCTCocoatainer alloc] init];

To register a class (concrete) with no dependencies to an initializer block

    [config registerComponent:[MyClass class] initsWith:
         return [[MyClass alloc] init];

To do the above with 1 dependency it would look like

    [config registerComponent:[DependsOn1 class]
                 dependentOn1:[SomeClass class]
                    initsWith:^(SomeClass* d1)
         return [[DependsOn1 alloc] initWithD1:d1];

To register a pre-allocated instance of a class

    MyClass* myClass = [[MyClass alloc] init];
    [config registerComponent:[MyClass class]

To resolve an instance of a registered class

    MyClass* testObject = [config resolveComponent:[MyClass class]];

To register a protocol (abstract) with 2 dependencies to an initializer block

    [config registerComponent:@protocol(MyProtocol)
                    initsWith:^(id<ProtocolD1> d1, id<ProtocolD2> d2)
         return [[MyClass2Deps alloc] initWithD1:d1 andD2:d2];

To resolve a component by protocol

    id<MyProtocol> myMug =
        [config resolveComponent:@protocol(MyProtocol)];

A class' dependents can be protocols, and a protocol's dependents can be classes. Here's what 6 class dependencies for a protocol looks like

    [config registerComponent:@protocol(IDependsOnMultiple)
                 dependentOn1:[MyClassA class]
                         and2:[MyClassB class]
                         and3:[MyClassC class]
                         and4:[MyClassD class]
                         and5:[MyClassE class]
                         and6:[MyClassF class]
     ^(MyClassA* d1, MyClassB* d2, MyClassC* d3,
       MyClassD* d4, MyClassE* d5, MyClassF* d6)
         // This init takes nil-terminated VA args
         return [[DependsOnMultiple alloc] initWithDependencies:
                 d1, d2, d3, d4, d5, d6, nil];

The shorthand for the above is shown below. While the above should be preferred because it is more explicit, this form below can handle any number of dependencies, whereas the above method has a limited number of overloads.

    [config registerComponent:@protocol(IDependsOnMultiple)
                  dependentOn:@[[MyClassA class],
                                [MyClassB class],
                                [MyClassC class],
                                [MyClassD class],
                                [MyClassE class],
                                [MyClassF class]]
     ^(NSArray* deps)
         // This init takes nil-terminated VA args
         return [[DependsOnMultiple alloc] initWithDependencies:
                 deps[0], deps[1], deps[2], deps[3], deps[4], deps[5], nil];

This example below is container scope nesting. Note, that an inner (descendant) container can resolve objects from the outer (ancestor) containers, but the outer containers cannot resolve objects from the inner. This is because the outer scope is wider than inner scopes, so there is no guarantee the inner scope is active.

    CCTCocoatainer* outerScope = [[CCTCocoatainer alloc] init];

    [outerScope registerComponent:@protocol(ILog)
                            return [[ArrayLog alloc] init];

        CCTCocoatainer* innerScope = [[CCTCocoatainer alloc] init];
        [innerScope addParent:outerScope];

        [innerScope registerComponent:@protocol(ILoggerA)
                            initsWith:^(id<ILog> log){
                                return [[DescopeLoggerA alloc] initWithLog:log];

        id testObject = [innerScope resolveComponent:@protocol(ILoggerA)];
    } // End of inner scope

    // ILoggerA will scope out and print a dealloc message here, while ILog is still in scope

CocoaMug Example in Swift

import Cocoatainer
        var container = CCTCocoatainer()

        var phws: AnyObject! = NSObject.protocolAsId(HotWaterSource.self)
        var ptop: AnyObject! = NSObject.protocolAsId(Topping.self)
        var pmix: AnyObject! = NSObject.protocolAsId(Mixture.self)
        var pmug: AnyObject! = NSObject.protocolAsId(LiquidVessel.self)

        container.registerComponent(phws, withInstance: Kettle())

        container.registerComponent(ptop, withInstance: Marshmallow())

            dependentOn1: ptop,
            { (top: AnyObject!) -> AnyObject! in
                CocoaPowder(topping: top as! Topping)

            dependentOn1: phws,
            and2: pmix)
            { (source: AnyObject!, mix: AnyObject!) -> AnyObject! in
                CocoaMug(source: source as! HotWaterSource,
                    mixture: mix as! Mixture)


        var mug: LiquidVessel =
            container.resolveComponent(pmug) as! LiquidVessel


Getting Familiar

Before using Cocoatainer in your own project, you may want to familiarize yourself with the framework. The following will help getting the Cocoatainer test harness and example code running.

  • Download the repo
  • In the root folder, open the Cocoatainer.xcworkspace file in XCode.
  • Under the CocoatainerExample project, the example code is called in the main.m file. Running it will print to the Console. Look at the CocoaMug example for practical uses of the container.
  • Under the CocoatainerGuiExample project, this example code will run a GUI application which contains buttons to control the lifecycle of an inner container. There is an outer container owned by IB which provides View dependencies to the inner container.
  • Under the CocoatainerSwiftExample project, there is a Swift port of the CocoaMug example, along with Swift unit tests.
  • Under the Cocoatainer project, in the CocoatainerTests folder there are several files, each containing several unit tests on the container. Many of the types are only setup for the purpose of testing the container, and may not be setup with the best practices in mind.

Getting Started

To start using Cocoatainer in your project, here's how you would set it up:

  • First, download a pre-built zip of the framework.
  • In the same directory as your XCode project, create a 'lib' directory. This directory should be a sibling of the .xcodeproj file.
  • Unzip the Cocoatainer-*.zip file into the newly created 'lib' directory so that the 'Debug' and 'Release' folders are direct children 'lib'.
  • In your XCode project's 'Build settings' located 'Framework Search Paths' and add $(PROJECT_DIR)/lib/$(CONFIGURATION) to the value.
  • In the 'General' section of your project settings, find 'Embedded Binaries'. Click the '+' and choose 'Add other', and browse to your 'lib' folder. Expand the 'Release' folder and choose the Cocoatainer.framework file.
  • You should now be able to #import <Cocoatainer/Cocoatainer.h> and start using it in your project.

Note, that according to this guide, the steps above will keep your project App Store submission-friendly. Worse case, you can download the Cocoatainer source and and the framework to your project.

Another tip is that if you don't like committing 3rd party binaries into your git repo (especially if you're keen on keeping them up-to-date), you can use git-fat to manage binaries on separate storage with version control.


Copyright (C)2015 Jeffrey Bakker. All rights reserved.
Released under the MIT license (see LICENSE.md for full text).


Jeffrey Bakker <jeffrey at seatoskyware dot com>