iOS - Add “objects” to existing app (jailbroken)

Question

How do you add \"objects\" to an existing app ?

For example, the EasyRefresh for Chrome tweak, enables a new button inside the iOS Chrome app, as do many other tweak

Answer 1

You need in order to do this to understand how the Objective-C runtime works. Especially the messaging system (ie. calling a method). In particular, the methods to call are determined at runtime, vs other languages where it is at compile time. This allows for global changing of particular methods, aka method swizzling.

Using the Mobile Substrate library you will be allowed to replace any method implementation with your own, and even call the original implementation. You need for that, of course, to know the method's name and the argument it takes, as well as the class it belongs to.

So to modify the SpringBoard for instance, you'd have to know which class in contains and which method. You'll have to use the class-dump or class-dump-z utility which does that for you (class-dump-z is more recent and more used for iOS dev, class-dump is more versatile and compatible with older binaries as well as 64 bit).

So to class-dump the SpringBoard, you'd need to enter in Terminal.app

class-dump -H /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.0.sdk/System/Library/CoreServices/SpringBoard.app/SpringBoard -o ~/Desktop/SpringBoard

For class-dump-z, the -p option will generate @property instead of getters/setters, which is more clear, so you'd probably type in

class-dump-z -p -H /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.0.sdk/System/Library/CoreServices/SpringBoard.app/SpringBoard -o ~/Desktop/SpringBoard

That line will create a folder on your desktop with all the classes definitions of SpringBoard. Of course you might need to change path to one suited to your system (about that, for recent versions of Xcode, the Developer folder is in Xcode, so you'd need something like

/Applications/Xcode/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.1.sdk/System/Library/CoreServices/SpringBoard.app/SpringBoard

You can also find on the internet people who did that for you for most of the existing frameworks, this is pretty handy if you make sure they are at the right version for you're system.

Now, for AppStore applications, you will first need to decrypt them as they are protected. You will probably need to find the names and links of that yourselves as this is probably against the ToS of Stack Overflow, though using gdb can achieve that purpose.

To ease the work, some tools such as Logos (you will probably also need to see Theos) has been created that reduce the boilerplate code needed. There also is a (quite old) xcode template & tutorial for mobilesubstrate that provides good help.

Logos makes it easy to hook method method from class classname :

%hook classname //declares the class from your application you're going to override

-(void)method {

    dosomethingnew(); //put all your new code for the method here
    return %orig;     //this calls the original definition of the method
}
%end //end hooking classname

For a list of the frameworks in the system and what they are usefull to, see here

Last thing : a list of popular tweaks that are opensourced (links to GitHub when possible) :

• Chrome Customizer
• MobileNotifier
• UISettings (iOS 5 version was here also but seems to be pulled ?)
• Spire
• IconRenamer
• Maxoimizer
• IconRotator
• QuickReply
• WinterBoard
• Veency

Some little tweaks

Finally, have a look at the WeekTweak, they release opensource tweak each week so you can learn by looking at someone else's source to try & do your own stuff. And the #theos chan on IRC (irc.saurik.com) will also provide help if you ask it kindly.