p7_mshookivar.md

How Do You Create a Tweak?

What is MSHookIvar?

MSHookIvar is a function present in the MobileSubstrate API, used to obtain ivar values of an object or instance. It can only be used in .xm files, so if it is needed to be used, the file should be renamed to have a .xm extension.

What is its syntax?

MSHookIvar<type>(object, name_of_ivar);

• type - This is the type of the ivar, so if the ivar for example is a UIView, then UIView * would be put there.
• object - This is where the ivar is located, so for example it could be self or an instance of a class.
• name_of_ivar - This is obviously the name of the ivar, it has to be written as a C string rather than an NSString, so no @ before the string.

Example use-case

#import <UIKit/UIKit.h>

%hook PSTableCell

-(void)didMoveToWindow {
    UITableViewLabel *detail = MSHookIvar<UITableViewLabel *>(self, "_detailTextLabel");
    detail.textColor = UIColor.redColor;
    %orig;
}

%end

Alternative to MSHookIvar

-valueForKey: is an alternative to MSHookIvar when it cannot be used. Its syntax looks like this:

[object valueForKey:name_of_ivar];

• object - This is where the ivar is located, so for example it could be self or an instance of a class.
• name_of_ivar - This is obviously the name of the ivar. In valueForKey it can be written as a NSString though. Bare in mind though that despite MSHookIvar "ugly" syntax, it tends to be more effective.

Another Example use-case

#import <UIKit/UIKit.h>

%hook PSTableCell

-(void)didMoveToWindow {
    UITableViewLabel *detail = [self valueForKey:@"_detailTextLabel"];
    detail.textColor = UIColor.redColor;

    %orig;
}

%end

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