Hooking Instance Variables

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This page is dedicated to the use of the MSHookIvar function, included in Cydia Substrate, to modify instance variables. This function is meant to be used when one can't get an instance variable through instance methods.

Header definition

template <typename Type_>
static inline Type_ &MSHookIvar(id self, const char *name);

Used like this:

type ivar = MSHookIvar<type>(object, ivar_name);

Where:

  1. type is a primitive type (int, char, struct CGRect, a pointer or a reference to), a C++ class or an Objective-C class (NSObject *, UILabel *).
  2. object is the variable that contains the target instance variable.
  3. ivar_name is a C string, not an Objective-C string (so no @ sign).

Example usage

// Given a private class
@interface SBIconController : NSObject {
	SBIconContentView *_contentView;
}
+ (id)sharedInstance;
@end

// In some block of code:
{
	...
	SBIconController *iconController = [%c(SBIconController) sharedInstance];
	SBIconContentView *contentView = MSHookIvar<SBIconContentView *>(iconController, "_contentView");
	// Would return the same as [[%c(SBIconController) sharedInstance] contentView];
	...
}