What is the difference between a static and dynamic library in XCode? And why doesn't Apple allow us to use dynamic libraries in our iOS applications?
While you can build dynamic libraries for Mac OS X, you cannot use them for iPhone development.
A static library is merely an archive of object files that gets pulled into a program linking against it. The linker will unarchive all the archive files, and pull them in during linking along with the rest of your object files.
A dynamic library however, creates a shared object file, akin to a program but without an entry point, which programs can link against and call out of themselves into these shared libraries for their symbols, without pulling them into itself.
A dynamic library wouldn't make any sense for an iphone app as there is no way to install the library on the phone. I remember reading some documentation where apple stated they decided not to use dynamic libraries as they didn't want users to have to deal with hassles of finding/updating libraries. Much easier to just install 1 bundle per app.
Apple does allow you to make dynamic libraries. On Mac OS X, these end in .bundle or .dylib (not .so or .a like on Linux).
What, specifically are you trying to do? Did you create a target for your dylib?
iOS static vs dynamic library
Static library(.a) - library which copies all it's content into a target at compile time. That is why compile time is slower and result file is bigger, but there is no delay in run time
Dynamic library(.dylib) - library which has a single copy in a system where linking happens during run time. That is why compile time is faster, footprint of output file is smaller but there are some delays in runtime. Dynamic library is prerogative of OS(a lot of system libraries are dynamic) and as a developer you are not able to create it. Since such type of library is shared between different applications it should be secure and support IPC
Dynamic framework - framework with Dynamic library inside. Apple presented Dynamic framework and App extension[About] from iOS v8. You are able to use it inside single application to share common code and resources inside app sandbox
[Vocabulary]
Related
I am creating an 'SDK' which will enable communication with a piece of custom hardware (via BLE, abstracting my comm protocol to async methods/callbacks, on various classes all Obj-C). I wish to package this SDK so I can distribute it to users so they can build apps using this hardware. I want to provide an .h file(s) and a pre-compiled library (closed-source).
What's the best practice here? Shall I choose to create a .framework, .a, .dylib?
what's the difference between them and their usage cases? what's the correct way to create the needed library?
many thanks
You cannot create dylib for iOS. User cannot link his project with that library dynamically on iOS, it is platform restrictions.
You can create framework or .a file (static library).
There can be some issues with resources from you library (framework)
It is dublicate question, see Difference between framework and static library in xcode4, and how to call them
As is known to everyone, static libraries can work well in an Iphone App and your App can be easily approved by IOS App Store
Unfortunately, the two static libraries I'm using now have the some C functions and variables.
so I compiled them into *.dylib (dynamic libraries), and copy them to "Bundle Resources" in XCode.
dylib_handle = dlopen(dylib_path_in_resource_bundle, RTLD_LAZY);
func = dlsym(dylib_handle, "func");
// invoke func();
This works well in simulator and Ipad (of course, different dynamic libraries).
I noticed that somebody said Iphone app does not support any third party dynamic libraries and my app will be rejected. (see here)
but I carefully read the "App Store Review Guidelines", I found no item meet my question.
I'm confused now!
Does iphone app support dynamic libraries? Does IOS AppStore allow this?
Who can give me an official response.
As Bernardo Ramos states in a comment: "Since iOS8 we can use dynamic libraries".
Dynamic libraries are not allowed by the App Store. No code may be loaded at run-time. The answer is to convert them to static libraries and compile them into the application.
From iPhoneOSTechOverview:
"If you want to integrate code from a framework or dynamic library into your application, you should link that code statically into your application’s executable file when building your project."
Read "should" as "must"
See SO Answer: Can create dynamic library for iOS?
No, dynamic libraries are not allowed.
But you can create static libraries, and even "static frameworks" (that is, like a classic framework is, a folder with the ".framework" extension and containing your Headers, resource files if any, and the lib itself, except that your lib must be a static library).
I have created a static library for my application. Now, my application uses sources like plists & images which I am referring in my application.
How can I bundle those images and deliver them with the static library and also what changes do I need to do in my source loading code to load it from that bundle.
Right now I using [UIImage imageNamed:"my.png"] to load the image.
A library cannot have "resources". A library will just provide some algorithm or logic to get the things done. So you cannot include any resources with in your library. Along with your library, you have to distribute the resources also. Or else the app that is using the library must have the resources with the same name that you hard coded.
That is exactly the reason to create a Framework - in a Framework you have:
A static library (with binaries for
simulator and phone melded together)
Include files a user of the framework
needs
Resources the framework needs, which
can be anything including .plist
files, images or xib.
Edit:
Removed link that was dead. You no longer need to know how to construct frameworks for iOS, because starting with iOS8 you can have Xcode create an iOS framework project.
In fact this is a great approach also, because frameworks can easily be imported into Playgrounds to call.
I am creating an SDK for a client that includes predefined view controllers. What is the recommended way to package everything (static lib, .xib(s), and .png(s)) for easy use?
SDKs that I've used (e.g. Pinch Media) do a good job of just providing a .h and .a file that expose only user accessible functionality and hiding everything else. As I read Apple's documentation, a framework would be ideal but is not permitted on iPhoneOS.
Some key requirements:
Don't expose source or object
internals.
Be easy to use & set up.
Work on both the device and simulator.
Thanks!
Frameworks would be ideal, but as you said, aren't allowed on the iPhone. I think in the end you'll need to provide at least 3 files: a header file, a static library, and a resource bundle.
The header file would simply have all the API's you do want to expose. If you have multiple classes you may want to provide multiple headers.
For the static library I recommend compiling it like normal for each architecture (Device and Simulator), and then use lipo to combine them like so (replacing paths as necessary):
lipo -create -output output/file/path device/file/path simulator/file/path
With the bundle you can make a new target in Xcode to create a bundle, but really it's just a folder. You would also need to make you're SDK know how to load the bundle, and get to the resources. You can't load executable code from the bundle however; that is the reason frameworks don't work on the iPhone.
Is it possible to create an own obj-C Cocoa Touch framework which can be used by other developers? And furthermore can you protect this framework?
I've created templates for Xcode 4 that allow you to build universal iOS frameworks (which work in both device and simulator).
Once the templates are installed, you simply select "Static iOS Framework" when creating a new project and it does the rest. It also works with unit tests.
https://github.com/kstenerud/iOS-Universal-Framework
You can create a static library. There is an option in the XCode project chooser to do this. You'll have to distribute the compiled static library file and the header files to users of your library. Your actual implementation files (.m) do not need to be distributed.
GHUnit does a good job of this - packaging up the libraries for both simulator and device - so I recommend looking at this project. (I also recommend using this library for unit testing :-)
The frameworks in Objective C are typically just C / ObjC code and a bunch of classes, nothing amazingly special. As such, you can create your own if you'd like, and then just include that in your project when you build it. The iPhone doesn't care about the difference, it just knows to put all that code into your app, along with everything else.
Have a look at the Framework Programming Guide on Apple's website. It will get you started. Essentially what you'll do is create a Framework project in XCode and then go from there.
As for "protecting" your framework, I assume you mean making your code unreadable. I'm not sure if and how you can do this, but perhaps Apple's guide will say something about it.
Yes you can create frameworks for use with Cocoa Touch.
However there are these caveats:
has to be a statically linked libary, no dynamic loading (dyld) for us
should be a combined (lipo) library for i386 (simulator), arm6 and arm7
you need to hack a bundle project into a framework
you should embed (small and few) images into the library so that the developer does not have to mess around with resources but just drags/drops it into his project
... or if you have large and many images build a bundle with these
I have guides for these things on my site.
1+2 = http://www.drobnik.com/touch/2010/04/universal-static-libraries/
The other links you have to google because this site does not let me post more than one URL.
You could make a static library available as binary (i.e. rudimentary "protection") to third parties, but not a dynamic one, as Apple's App Store policy prevents dynamic linking.
Take a look at a worked example for static libraries given at
this site
If you're going to do it, in my opinion JSON.framework is a great example to follow. To hide/obfuscate the source code is a different story, and a different question entirely,
When creating a new project, navigate to iOS > Framework & Library > Cocoa Touch Framework, it's as simple as that. When you are successfully compile, .framework will be created under Products folder in XCode. Right click to show in Finder, and you can find the output.
It's unlikely this will work the way you want it to because the other developers won't be able to use your framework. This StackOverflow Question explains why.