p2_syntax.md

How Do You Create a Tweak?

But how do we actually write code for the tweak?

Great question! Let's begin writing some code! As said previously, we will be writing this code in Objective-C. We will not be using "pure" Objective-C however, we will be using something called Logos which is a "tool" made to make hooking easier.

Let's go step by step.

We will make a tweak to hide the status bar!

First, go to your Tweak.x file. There will be a huge block of comments made there when the tweak was made by Theos. Feel free to read this, it is actually recommended to get a first glance on what the syntax is like.

We will first import UIKit. UIKit is a framework containing all the basic UI elements you see in an iOS app, such as buttons, switches, sliders, etc. This can be done like so:

#import <UIKit/UIKit.h>

or like so:

@import UIKit;

This is needed for pretty much all tweaks.

Then we will use the FLEX tweak to find the correct view to hook. How do we get it? Well let's see! Make sure you're doing this on the HomeScreen as we are hooking the SpringBoard.

1. Trigger the FLEX menu (the instructions to this are likely in the tweak description.)
2. Press the select button on the FLEX menu.
3. Then press the status bar somewhere that there is no text.
4. After that, press the views button. FLEX will automatically scroll down to the selected view.
5. Press the (i) button next to the view.
6. This is where we will find all the properties, ivars, methods, etc. pertaining to the view. In this case, we want to modify the hidden property of the view.
7. Find where it says @property BOOL hidden, press the (i) button next to it, and then flip the switch. Press done and you should see (or rather not see!) the hidden status bar!

Great! Now how do we write this in code?

First, we will find the view we are hooking. In our case, it is called _UIStatusBarForegroundView. This view inherits from UIView. You can check what a view inherits its properties from in FLEX by clicking on the (i) button next to the view and then looking at the top bar, where it should say _UIStatusBarForegroundView, then UIView, then UIResponder, and then finally NSObject. This means that _UIStatusBarForegroundView is inheriting its properties from UIView which is inheriting them from UIResponder, and so forth. So say UIView has a "hidden" property... _UIStatusBarForegroundView would also have a "hidden" property because it inherits from UIView.

UIKit only recognizes simple classes such as UIView, UIViewController, etc. so we will have to "interface" the view that we are hooking. This can be done like so:

@interface _UIStatusBarForegroundView : UIView // _UIStatusBarForegroundView inherits from UIView
@end

Alright, good! We've learned how to interface a view! Now it's time to hook it!

Logos provides an easy way to hook, it's as simple as... %hook! Basically, this is what we do.

%hook _UIStatusBarForegroundView
%end

%end is used to end the hook, so you could add a new one.

Now we need to override a method which is called by the view. Basically, a method is a "function" which gets called when a certain condition is met. So let's take as an example didMoveToWindow. As seen on its documentation page, the view is called when its "window object" changes.

How do we override it though? Well, it is easy to do. On the its documentation page, you can copy the code seen. It is the code for the method.

-(void)didMoveToWindow;

We need to change its function though, and it can be done by changing the semi-colon (;) to brackets, and then adding your new code there. Let's just say we want to print "Hello world!" to the console, for this we would use a function called NSLog. This can be done like so:

-(void)didMoveToWindow {
    NSLog(@"Hello world!");
}

If you need to initiate (call) the code that was written there originally, you can use %orig; to do that. So, looking at our previous example, we could do:

-(void)didMoveToWindow {
    %orig;
    NSLog(@"Hello world!");
}

You can put %orig; before OR after your code, or not put it at all. If you want the original code to run AFTER your code, then put the %orig; AFTER your code, if you want it BEFORE, then BEFORE.

Okay, but how do we hide it? Well, we know that hidden is a property of UIView, which _UIStatusBarForegroundView inherits from, so we could do: self.hidden = YES; (Note: you do not have to use YES, you could use true instead, or even 1 [true] and 0 [false]). self is referring to the view that we are hooking. So if we were to combine all this together, we would have something like this:

#import <UIKit/UIKit.h>

@interface _UIStatusBarForegroundView : UIView // _UIStatusBarForegroundView inherits from UIView
@end

%hook _UIStatusBarForegroundView

-(void)didMoveToWindow {
    %orig;
    self.hidden = YES;
}

%end

Compiling the tweak

make package -j

This is the simplest way to compile your tweak, there are many flags to get different results, however this is the simplest way.

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