# Code Customizations¶

Based on Loop users’ experience, there are some customizations that you may want to incorporate ahead of building your Loop app and Apple Watch app. These customizations must be done prior to building the Loop app onto your iPhone, they cannot be done from within the app itself. If you are an experienced builder - you know what to do.

## Build then Customize¶

For new builders, please build the code before you make any changes. Start with Open Loop and familiarize yourself with the interface. Later, you can make the customization(s) you desire (using Xcode as your editor) on the same download as the original build and then build again to the phone. The second build will be much faster than the first build.

### Find My Dowloaded Loop Code¶

Refer to the graphic below. The Downloads folder in Finder is highlighted on the upper left. The full path to Loop.xcworkspace is highlighted along the bottom.

• Open Finder
• Open that folder, for example, Downloads/BuildLoop/Loop-220803-1145, and inside that folder open the LoopWorkspace folder
• You can then make the customizations and build to your phone

Experienced Builders

Experienced builders will often build a fresh download to a simulator for their phone iOS (not their phone) to ensure download is good and is compatible with macOS, Xcode and phone iOS. Once the build is successful, they apply their customizations and build again to the simulator. Last step is to build the customized version to their real phone.

Be sure to read the Instructions for Finding the Lines.

Line numbers may change

Every effort will be made to update the line numbers as the code is updated, but there may be times where the screenshots and line numbers differ from the current version of Loop code.

• You may notice some customizations list line numbers for different branches

• If you cannot identify a line that looks exactly like the example - do not guess - go to your favorite social media group and ask for help

Loop 2.2.x vs Loop 3 (Loop-dev)

• Loop-dev is still being tested - but when it is released it will be Loop 3.
• To simplify the amount of changes required after the release, the labels indicate Loop 2.2.x or Loop 3, if needed.
• Users of Loop Master refer to the Loop 2.2.x examples.
• Users of Loop-dev refer to the Loop 3 examples.
• Note that some changes are in a different file for Loop-dev (part of the architecture upgrade for the app).

## Instructions for Finding the Lines¶

For each customization, you will be given landmarks to find the correct location in the code. You can choose to search using the Key_Phrase or navigate to the file in the folder structure and look for (cmd-L #) the line number. Note that the folder is listed with respect to the LoopWorkspace directory.

For each change you make in Xcode - be sure to save the file - otherwise the modification does not get built into your app.

Key_Phrase
use the copy button at right, paste into search

• Folder: Loop/subfolder1/subfolder2/etc.
• File: filename.swift, line number(s)

There may be a figure illustrating the change.

Below the figure, the original, and in some cases, the modified code will be displayed as text.

• Most customizations show the original line of code that you will be changing
• Sometimes that line is long and you may need to use the scroll bar to see the entire line in LoopDocs
• In most cases, an example customization is shown to assist you in deciding how to edit the line to meet your needs

To search using the Key_Phrase (see graphic below for clarification):

• A copy button is available when you hover your mouse in the right-hand side of the block below the title Key_Phrase; click on it to copy the phrase
• In Xcode, tap the Find menu item and select Find in Workspace
• Paste the text into the Find search-box that opens on upper left of Xcode screen and hit enter
• You should see a message 1 result in 1 file (for most cases)
• Some customizations will show more than one result, but that will be explained in the directions for that customization
• The file in which the line is located is reported showing the line in that file containing the Key_Phrase
• Click on the one you think is correct and it will display in the main middle window of Xcode with the Keyword highlighted on the line you selected
• The Key_Phrase was selected to limit the search to just the relevant line (if possible)
• In some cases, the Key_Phrase gets you close but not exactly on the line where you need to make the modifications - please read carefully

### Folders and Icons¶

The folders listed in the code customization steps below are the actual directory names as stored on your computer. However, a shortened name is used for some folders when being displayed as icons in Xcode. Some people prefer to search through the folder icons to find a file instead of using the Find in Workspace feature.

In the graphic below, the user searched for an item found for both Eros and DASH pods (in two different files). The top part of the graphic shows the result of the search with user clicking on one instance. On the right side of the top graphic (highlighted by red rectangle) is the name of the selected file on the computer with the full directory name.

• Inset 1: User clicked on the folder icon (highlighted by red square) to see the list of icons for folders included in the LoopWorkspace
• Inset 2: User opens folders under RileyLink icon to open OmniKit, then OmnipodCommon to find the Pod.swift file

These folder icon names are different from the directory names on the computer:

Folder Icon Name Directory Name
ShareClient dexcom-share-client-swift
Amplitude Amplitude-iOS

All other icons and directory names match.

## Disable Authentication for Bolusing¶

Depending on your iPhone preferences and model, you may have Face ID or Touch ID enabled. Those security features will also be used to authenticate bolus delivery in Loop. You can choose to disable authentication (i.e., not require Face ID, Touch ID, or passcode for bolusing) through the following code customization.

Loop 3

For Loop 3 (under test as Loop-dev), this controls the authorization requirement to modify Therapy Settings as well as to confirm bolus delivery.

Key_Phrase
canEvaluatePolicy(.deviceOwnerAuthentication

• Loop 2.2.x
• Folder: Loop/View Controllers
• File: BolusViewController.swift, Line 529
• Loop 3
• Folder: LoopKit/LoopKitUI/Extensions/
• File: Environment+Authenticate.swift, Line 20

The screenshot below was taken with Loop v2.0 when the line number was 201; with Loop 2.2.x versions, that same code is found at line 529. Add the false && as shown in the screenshot below:

#### Loop 2.2.x¶

Code Before Modification

if context.canEvaluatePolicy(.deviceOwnerAuthentication, error: nil) {


Code After Modification

if false && context.canEvaluatePolicy(.deviceOwnerAuthentication, error: nil) {


#### Loop 3¶

Code Before Modification

if context.canEvaluatePolicy(.deviceOwnerAuthentication, error: &error) {


Code After Modification

if false && context.canEvaluatePolicy(.deviceOwnerAuthentication, error: &error) {


## Default Carb Absorption Times¶

Loop’s default carb absorption times are based on the high, medium, and low glycemic index absorption curves presented in Think Like A Pancreas by Gary Scheiner. With Loop 2.2.x, the lollipop (fast) icon is set for 2 hours, taco (medium) icon for 3 hours, and pizza (slow) icon for 4 hours. This is modified for Loop 3 to 30 minutes, 3 hours and 5 hours respectively.

Key_Phrase
defaultCarbAbsorptionTimes: CarbStore.DefaultAbsorptionTimes

• Loop 2.2.x

• Folder: Loop/LoopCore
• File: LoopSettings.swift
• Line: 16 (2.2.4 master), 41 (2.2.4 AB), 50 (2.2.5 and later)
• Loop 3

• Folder: Loop/LoopCore
• File: LoopCoreConstants.swift
• Line: 16

For example, if you wanted to modify Loop 2.2.9 so that lollipop represents a 30 minute absorption and pizza a 5 hour absorption, the edit would be as follows:

Code Before Modification for Loop 2.2.x

public static let defaultCarbAbsorptionTimes: CarbStore.DefaultAbsorptionTimes = (fast: .hours(2), medium: .hours(3), slow: .hours(4))


Code After Modification or default for Loop 3

public static let defaultCarbAbsorptionTimes: CarbStore.DefaultAbsorptionTimes = (fast: .minutes(30), medium: .hours(3), slow: .hours(5))


Note that if you change from 2 hours to 30 minutes, you must also change the indication before the parentheses.

## Adjust Percent Bolus for Automatic Bolus¶

If you are mostly happy with the Dosing Strategy of Automatic Bolus but wish it delivered more or less insulin during every Loop interval, then this customization is for you.

This customization changes the percent of the recommended bolus used for automatic delivery. The method for calculating that recommendation is not changed by this modification. The default value is 40% (0.4). It is recommended you take small changes of 0.1 at a time. Once you modify it once and try it out for a while, it’s easy to go back and change it again.

With Loop 2.2.x, the end of the line has a comment // %, whereas with Loop 3, there is an explanatory comment (line starting with //) before the line.

Change just the number and double check that the value is less than 1.

Key_Phrase
let bolusPartialApplicationFactor

• Loop 2.2.x

• Folder: Loop/LoopCore
• File: LoopSettings.swift
• Line: 89 (2.2.5 and later)
• Loop 3

• Folder: Loop/Loop/Models
• File: LoopConstants.swift
• Line: 44

Code Before Modification

public let bolusPartialApplicationFactor = 0.4


Code After Modification to 50% of recommended insulin

public let bolusPartialApplicationFactor = 0.5


Do not exceed 1.0

This number should never be bigger than 1 (you’d be getting more than Loop recommends). If you think you need more than 1, consider your settings and meal entries.

## Modify Override Sensitivity¶

Some people want finer settings on the override sensitivity picker and may want to limit the overall range for overrides – especially for children.

1% Settings Available without Customization

With the advent of Loop 3, the Override Sensitivity values are not limited by the default picker values of 10%.

Any override more than a factor of 2 from 100% can cause Loop predictions to be wrong – especially if a carb count is entered. (An override is NOT the same as a manual temp basal - it changes insulin sensitivity factor and carb ratio in addition to the basal rate needed for zero change in IOB for the duration of the override.)

This example customization changes the lower bound for sensitivity to 50% (factor of 2 smaller than 100%) and provides 5% steps.

Key_Phrase
let allScaleFactorPercentages

• Loop 2.2.x and Loop 3
• Folder: LoopKit/LoopKitUI/Views
• File: InsulinSensitivityScalingTableViewCell.swift, Line 19

Code Before Modification

private let allScaleFactorPercentages = Array(stride(from: 10, through: 200, by: 10))


Code After Modification to 50% to 200% by steps of 5%

private let allScaleFactorPercentages = Array(stride(from: 50, through: 200, by: 5))


## Modify Maximum Carb Entry¶

Some people want to limit the maximum number of carbs that can be entered in one entry – especially for children or folks who eat lower carb. This helps prevent accidental typos, e.g., entry of 115 g instead of 15 g for a meal.

Key_Phrase
maxQuantity =


As shown in the graphic below, this phrase shows up in 2 places, only the first one should be modified.

• Loop 2.2.x and Loop 3
• Folder: Loop/Loop/View Controllers
• File: CarbEntryViewController.swift, Line 33 (Loop 2.2.x) or 36 (Loop 3)

Code Before Modification

var maxQuantity = HKQuantity(unit: .gram(), doubleValue: 250)


Code After Modification to limit carb entry to 99 g

var maxQuantity = HKQuantity(unit: .gram(), doubleValue: 99)


## Pods: Add Extra Insulin on Insertion¶

The default value is 0.0 u of extra insulin. If you use this customization, start with a small number and work your way up. If you are coming from manual podding and routinely gave yourself an extra bolus with your PDM at pod change time, you may not need nearly as much with Loop - be conservative.

Note that Loop does not include the amount of insulin in the prime or insertion steps in your IOB. The pod reports every pulse that it delivers to Loop. If you look in the Pod Settings insulin delivered row, that is the total delivered by the pod minus the (prime plus insertion) amounts. The only way to know that you successfully made this change is to count the clicks. Normal insertion is 0.5 U (0.5 U / 0.05 U per click = 10 clicks). So if you add 0.35 U to the "extra" value, you should get 0.35 / 0.05 = 7 extra clicks. In other words, 17 total clicks after you press insert.

This code change is found in one location for Eros Pods (called Omnipod throughout the app) and DASH Pods (called Omnipod Dash throughout the app). I tend to change both files, but if you're only using one kind of pod, that is really not necessary.

Key_Phrase
let cannulaInsertionUnitsExtra

• Loop 2.2.x: Eros Pod (ones that require a RileyLink compatible device)
• File: Pod.swift, Line 72 (Loop 2.2.x)
• Eros or DASH Pod (Loop 3 only)
• Folder: OmniBLE/OmniBLE/OmnipodCommon (DASH)
• File: Pod.swift, Line 87 (Eros); Line 82 (DASH)

When finding the file using the folder icons in Xcode, instead of using the Key_Phrase in Find in Workspace, the RileyLink icon represents the rileylink_ios folder name on the computer.

Code Before Modification

public static let cannulaInsertionUnitsExtra = 0.0 // edit to add a fixed additional amount of insulin during cannula insertion


Code After Modification to add 0.35 U

public static let cannulaInsertionUnitsExtra = 0.35 // edit to add a fixed additional amount of insulin during cannula insertion


## Modify the Guardrails¶

The Therapy Setting Guardrails are for Loop 3 (Loop-dev) only.

If you build Loop-dev over a version of Loop 2.2.x or FreeAPS where the Correction Range is lower than the default value of 87 mg/dL (4.8 mmol/L), your app will crash when you try to onboard.

The solution (until this is fixed) is to customize and lower the minimum value to be at or below the value you have currently set. Rebuild the app with the modified settings and you should be able to continue the onboarding process.

Key_Phrase
Guardrail(absoluteBounds:

• Loop 3 only
• Folder: LoopKit/Extensions
• File: Guardrail+Settings.swift
• Line: 12 for suspendThreshold
• Line: 26 for correctionRange

Code Before Modification

static let suspendThreshold = Guardrail(absoluteBounds: 67...110, recommendedBounds: 74...80, unit: .milligramsPerDeciliter, startingSuggestion: 80)


and

static let correctionRange = Guardrail(absoluteBounds: 87...180, recommendedBounds: 100...115, unit: .milligramsPerDeciliter, startingSuggestion: 100)


Modify the 67 for suspendThreshold or 87 for correctionRange to the desired value. Loop automatically converts from mg/dL. So you must enter values reasonable for mg/dL (18 times higher than for mmol/L).

If fixing a crashed app during onboarding, you must lower the 87 to match or be less than what is in your old settings.

## Adjust Future Carbs Time Interval¶

Loop 3 (Loop-dev) limits the future time change allowed to 1 hour.

Key_Phrase
cell.datePicker.maximumDate = date.addingTimeInterval

• Loop 3 only:
• Folder: Loop/Loop/View Controllers
• File:CarbEntryViewController.swift
• Line: 361
• Default shown below (for maximum and minimum):

Code Before Modification

cell.datePicker.maximumDate = date.addingTimeInterval(.hours(1))


Change the maximumDate to the number of hours in the future you desire. Remember that Loop may increase insulin dosing for future carbs - make sure that they actually arrive.

The minimumDate is how far back in the past you can modify time. The default is 12 hours in the past.

## Adjust the Watch Crown Sensitivity¶

The rate of change of the carb and bolus entry pickers when using the digital crown can be altered as can the rotation required to confirm a bolus on the watch. If you are running an older series watch - you may want to make these customizations. When I switched from Series 3 to Series 7 watch - it was amazing. I got a graph on the main watch screen I didn't even know existed and the bolus acceptance was a breeze!

There are a number of places where you need to make changes (2 for sensitivity and 2 for bolus confirmation for Loop 2.2.x), so walk though them one at a time. For the Watch Crown Sensitivity, the 1/24 value is the ratio of rotations of the crown to the amount of change in the value. Changing it to 1/12 would mean that half as many turns would be needed for the same amount of carb or bolus entry.

• The Loop 2.2.x customizations are throughly tested by many users.
• The Loop 3 customization is provided from code inspection and one test - use with care.

### Loop 2.2.x Sensitivity¶

Key_Phrase
let rotationsPerIncrement

• Folder: Loop/WatchApp Extension/Controllers
• Initial Value: 1/24; try 1/12 to increase change in picker value for a given motion

Key_Phrase
let rotationsPerValue

• Folder: Loop/WatchApp Extension/Controllers
• File: BolusInterfaceController.swift, Line: 191
• Initial Value: 1/24; try 1/12 to increase change in picker value for a given motion

### Loop 2.2.x Bolus Confirmation¶

In order to reduce the amount the user has to spin the watch crown to confirm a bolus, there are 3 numbers on 2 lines that must be modified. You will be working in the same file you just used to modify the watch sensitivity to adjusting the bolus amount, BolusInterfaceController.swift.

For example to change rotation required to 70% of the default, change 1.0 to 0.7 in 3 places on those 2 lines. This Key_Phrase returns 3 lines, the second 2 of which are the ones in that file where the change is required:

Key_Phrase
abs(accumulatedRotation)

• Folder: Loop/WatchApp Extension/Controllers
• File: BolusInterfaceController.swift, Lines: 311 and 360
• Initial Value: 1.0; try 0.7 to decrease how much is needed to confirm bolus

### Loop 3 Digital Crown Adjustments¶

These are new instructions and the user should take care - and please report back if you have problems.

First - try it with no customization. Then make small changes.

This key phrase will indicate three different files in the same folder as shown in the graphic below - you can adjust each in turn as you desire. When you click on the line, the quantity you change is a few lines below where you find the Key_Phrase, except for the CarbAndDateInput file.

Key_Phrase
.digitalCrownRotation

• Folder: Loop/WatchApp Extension/Views/Carb Entry & Bolus

#### Modify Bolus Confirmation Motion¶

• File: BolusConfirmationView.swift, line 59
• Initial Value for scalingRotationBy is 4
• Decrease to require less motion to confirm bolus (use whole numbers only), start with 3

#### Modify Bolus Picker Sensitivity¶

• File: BolusInput.swift, line 53
• Initial Value for rotationsPerIncrement is 1/24
• A change to 1/12 increases the change in picker value for a given motion

#### Modify Carb and Time Picker Sensitivity¶

• File: CarbAndDateInput.swift, line 68
• Initial Value for rotationsPerIncrement is 1/24
• A change to 1/12 increases the change in picker value for a given motion

An expiration notification feature has been added to Loop. You get a notification when you open the Loop app to alert you that the expiration is approaching. (Not available with version v2.2.4 and earlier.)

If you prefer a different notification time and frequency, there are two lines you can modify:

• Loop 2.2.x and Loop 3
• Folder: Loop/Managers
• Line 16: modify how long before expiration you get the FIRST notification
• Line 28: modify how frequently you will be notified
Key_Phrase
expirationAlertWindow: TimeInterval

Key_Phrase
 minimumTimeBetweenAlerts: TimeInterval


Default code for line 16:

    static let expirationAlertWindow: TimeInterval = .days(20)


• 30 days: change .days(20) to .days(30)
• 12 hours: change .days(20) to .hours(12)

Default code for line 28:

    let minimumTimeBetweenAlerts: TimeInterval = timeUntilExpiration > .hours(24) ? .days(2) : .hours(1)


Modify Frequency of Repeated Notifications (Three Values):

• This phrase: > .hours(24) ? .days(2) : .hours(1)
• Rewritten as: > Time_A ? Frequency_A : Frequency_B, means:
• Use Frequency_A if there is more time between now and the expiration date than Time_A
• Use Frequency_B if there is less time between now and the expiration date than Time_A

You can enter Time or Frequency as .days(value), .hours(value) or .minutes(value).

Free App Users:

An example change that a Free Loop App user (who has to build once a week) might choose is:

     > .hours(4) ? .days(10) : .hours(2)

Combined with an .hours(12) on line 16, they would get notified at 12 hours, 4 hours and 2 hours before expiration on the day of expiration and only when the app is opened. Since you'll be building once a week, you can play around with these values until you are happy.

## Exponential Insulin Curve¶

The Exponential Insulin Curve Models (Rapid-Acting Adult, Rapid-Acting Child, and Fiasp) default to an insulin duration of 360 minutes...but the peak activity of the various curves differs, as follows:

• Rapid-acting adult curve peaks at 75 minutes
• Rapid-acting child curve peaks at 65 minutes
• Fiasp peaks curve peaks at 55 minutes

If you wish to customize these values, please make sure you know what you are doing. This is not a modification recommended for Loop novices. For Loop 3 users, the file is in a different submodule and includes more models.

Key_Phrase
MARK: - Model generation

• Loop 2.2.x
• Folder: Loop/LoopCore/Insulin
• File: ExponentialInsulinModelPreset.swift
• Lines:
• actionDuration (20 to 29)
• peakActivity (31 to 40)
• effectDelay (42 to 51)
• Loop 3 << NOTE more models
• Folder: LoopKit/LoopKit/Insulin/ << NOTE new location
• File: ExponentialInsulinModelPreset.swift
• Lines:
• actionDuration (19 to 32)
• peakActivity (34 to 47)
• effectDelay (49 to 62)

If you want an app logo other than the default green circle for your Loop app, you can easily customize this. To make it easy to generate the correct sizes of icons, you can use a site like appicon.build or appicon.co and just drag and drop your source image. The source image needs to be 1024 pixels x 1024 pixels. The site will email you a zip file or automatically download a set of files. Highlight and copy the contents of the Appicon.appiconset that you are sent, including the Contents.json file

Use Finder to Navigate to the LoopWorkspace folder. These instructions assume you used the Build-Select Script - if your files are in a different folder, make the appropriate adjustment.

1. Use Finder to navigate to Downloads / BuildLoop and open the folder with the most recent date (e.g., Loop-Master-211006-0524)
2. Double-click on the LoopWorkspace folder
3. Double-click on the AdditionaAssets.xcassets folder
4. Double-click on the CustomLoopIcon.appiconset folder
5. Replace the contents of the Appicon.appiconset with your copied images and Contents.json file.

You may see a yellow alert that there are “unassigned children” depending on the images the app icon generator tool produced. The unassigned children alert will not prevent your app from building, it’s simply because there are more sizes of images than Loop app uses. You can just leave the unassigned children alone (wow...how often do you get to say that phrase?).

And now you'll be the proud new owner of a custom Loop icon.