Network storage design pattern - objective-c

Question

Let's say I have a few controllers. Each controller can at some point create new objects which will need to be stored on the server. For example I can have a RecipeCreationViewController which manages a form. When this form is submitted, a new Recipe object is created and needs to be saved on the server.
What's the best way to design the classes to minimize complexity and coupling while keeping the code as clean and readable as possible?
Singleton
Normally I would create a singleton NetworkAdapter that each controller can access directly in order to save objects.
Example:
[[[NetworkAdapter] sharedAdapter] saveObject:myRecipe];
But I've realized that having classes call singletons on their own makes for coupled code which is hard to debug since the access to the singleton is hidden in the implementation and not obvious from the interface.
Direct Reference
The alternative is to have each controller hold a reference to the NetworkAdapter and have this be passed in by the class that creates the controller.
For example:
[self.networkAdapter saveObject:myRecipe];
Delegation
The other approach that came to mind is delegation. The NetworkAdapter can implement a "RemoteStorageDelegate" protocol and each controller can have a remoteStorageDelegate which it can call methods like saveObject: on. The advantage being that the controllers don't know about the details of a NetworkAdapter, only that the object that implements the protocol knows how to save objects.
For example:
[self.remoteStorageDelegate saveObject:myRecipe];
Direct in Model
Yet another approach would be to have the model handle saving to the network directly. I'm not sure if this is a good idea though.
For example:
[myRecipe save];
What do you think of these? Are there any other patterns that make more sense for this?

Answer 1

I would also stick with Dependency Injection in your case. If you want to read about that you will easily find good articles in the web, e.g. on Wikipedia. There are also links to DI frameworks in Objective C.
Basically, you can use DI if you have two or more components, which must interact but shouldn't know each other directly in code. I'll elaborate your example a bit, but in C#/Java style because I don't know Objective C syntax. Let's say you have
class NetworkAdapter implements NetworkAdapterInterface {
void save(object o) { ... }
}
with the interface
interface NetworkAdapterInterface {
void save(object o);
}
Now you want to call that adapter in a controller like
class Controller {
NetworkAdapterInterface networkAdapter;
Controller() {
}
void setAdapter(NetworkAdapterInterface adapter) {
this.networkAdapter = adapter;
}
void work() {
this.networkAdapter.save(new object());
}
}
Calling the Setter is where now the magic of DI can happen (called Setter Injection; there is also e.g. Constructor Injection). That means that you haven't a single code line where you call the Setter yourself, but let it do the DI framework. Very loose coupled!
Now how does it work? Typically with a common DI framework you can define the actual mappings between components in a central code place or in a XML file. Image you have
<DI>
<component="NetworkAdapterInterface" class="NetworkAdapter" lifecycle="singleton" />
</DI>
This could tell the DI framework to automatically inject a NetworkAdapter in every Setter for NetworkAdapterInterface it finds in your code. In order to do this, it will create the proper object for you first. If it builds a new object for every injection, or only one object for all injections (Singleton), or e.g. one object per Unit of Work (if you use such a pattern), can be configured for each type.
As a sidenote: If you are unit testing your code, you can also use the DI framework to define completely other bindings, suitable for your test szenario. Easy way to inject some mocks!