#import <substrate.h> // necessary
#import <Foundation/Foundation.h>

@interface TheClassYouAreHooking : NSObject {
    NSString *_exampleVariable;
}
- (void)doSomething;
@end

NSString *_exampleVariableHooked;

%hook TheClassYouAreHooking
- (void)doSomething 
{
    // 'Hook' the variable
    exampleVariableHooked = MSHookIvar<NSString *>(self, "_exampleVariable");
 
    exampleVariableHooked = @"Hello World";

}
%end

MSHookIvar 還能hook BOOL floats 等 .

exampleVariableHooked = MSHookIvar<BOOL>(self, "_someBOOL");

來自：https://stackoverflow.com/questions/11918934/theos-trying-to-take-over-uiview-subjectline-from-ckcontententryview-in-chatki