Objective C Dependency Injection Library (OIL) is a tiny dependency injection library for Objective C consisting only of one class. It supports both setter and initializer injection, singletons and protocol bindings. All Configuration is done in the source code itself, so there is no need for config files.
Download and extract OILContainer.zip in your project directory. It contains only OILContainer.h and OILContainer.m. Add these files to your XCode project.
The code below creates a new container and uses this container to create an instance of the class 'MyClass'.
//First, set up an OILContainer
OILContainer* myContainer = [[OILContainer alloc] init];
//To get a new object of class MyClass, do this:
MyClass *myObject = [myContainer getInstance:[MyClass class]];OIL will instantiate myObject by simply calling [[MyClass alloc] init].
If you want OIL to use a different init method, or if you want to set certain instance variables directly after creation of the object, you need to provide an OILInitBlock. Each class can have one init block. Init blocks are executed, when getInstance is called. They do all initialisation and return the object.
//Set up an OILContainer
OILContainer* myContainer = [[OILContainer alloc] init];
//This tells OILContainer what to do if the user wants a new instance of 'MyClass':
[myContainer setInitializer:^(OILContainer container){
id myObject = [[MyClass alloc] initWithNumber:5]; //calling custom init method
myObject.attribute = @"test"; //setting an inistance variable
} forClass:[MyClass class]];
//Get a new instance of MyClass. It will be initialized with the init block which we just provided.
MyClass *myObjec = [myContainer getInstance:[MyClass class]];Init blocks take an OILContainer and return the Object which they initialized.
It is possible to bind a protocol to a certain class which implements the protocol like this:
//Set up an OILConteainer
OILContainer* myContainer = [[OILContainer alloc] init];
Protocol* person = @protocol(Person); //'Person' is a protocoll which is implemented by 'Author'
[myContainer setInitializer:^(OILContainer* cont){return (id)[[Author alloc] initWithFirstName:@"HG" andLastName:@"Wells"];} forProtocol:person];
id<Person> myPerson = [myContainer getInstanceForProtcol:person]; //myPerson is an instance of 'Author'
You can mark a certain class or protocol as singleton, by calling the markClassAsSingleton or markProtocolAsSingleton methods like so:
[myContainer markClassAsSingleton:[MyClass class]];
[myContainer markProtocolAsSingleton:@protocol(MyProtocoll)];Singletons are created lazily, as soon as they are needed.
Use [OILContainer container] to get the global OILContainer object. It is not ensured or assumed that this is the only container in the app.
To use setter injection, your class needs to implement the empty OILInjectable protocol. To inject an object, create a property called injecedClass of type Class. In the following example, the injected class in called Author so the property is called injectedAuthor.
Setter injection currently only works with the global container and with concrete classes.
Book.h
#import "Author.h"
#import "OILContainer.h"
@interface Book : NSObject <OILInjectable>{
NSString* title;
Author* author;
}
-(Book*)initWithTitle:(NSString*)theTitle;
-(Book*)initWithTitle:(NSString*)theTitle andAuthor:(Author*)theAuthor;
@property (nonatomic, retain) NSString* title;
@property (nonatomic, retain) Author* injectedAuthor;
@endInjected properties can be overwritten like normal properties. (e.g. for unit testing)
In some cases, an object created by OIL is based on other objects which themselves need to be instantiated by OIL. As an example, consider the following Classes:
Author.h
@interface Author : NSObject {
NSString* firstName;
NSString* lastName;
}
-(Author*)initWithFirstName:(NSString*)theFistName andLastName:(NSString*)theLastName;
@endBook.h
@interface Book : NSObject {
NSString* title;
Author* author;
}
-(Book*)initWithTitle:(NSString*)theTitle andAuthor:(Author*)theAuthor;
@endThe class 'Book' depends on 'Author'. In order to let OIL create both the book and the author with their designated initializers, you need to call OIL in the initialization code like this:
//Set up an OILConteainer
OILContainer* myContainer = [[OILContainer alloc] init];
//Set initializer for 'Author'
[myContainer setInitializer:^(OILContainer* cont){
return (id)[[Author alloc] initWithFirstName:@"Herbert George" andLastName:@"Wells"];
} forClass:[Author class]];
//Set initializer for 'Book'
[myContainer setInitializer:
^(OILContainer* cont){
return (id)[[Book alloc] initWithTitle:@"The Time Machine" andAuthor:[cont getInstance:[Author class]]];
} forClass:[Book class]];
//Create book instance
Book* myBook = [testContainer getInstance:[Book class]];OIL now creates the book with the author HG Wells.
###The MIT License (MIT) Copyright (c) 2012 Julian Dax
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
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