iOS app size-reduction cheat sheet

Here you will find some advices and configurations to reduce iOS app size.

General recommendations

Use final class attribute in classes if no other class can inherit from it.
Use private whenever you can.
Avoid open/public if you don’t need them.
Use static libraries instead of dynamic ones.
- This will only reduce the size if you don't have the -ObjC flag, if you do, don't remove it! you don't want to screw up the linking of your project, right?
- Independently of -ObjC flag, I still recommend that you migrate to static instead of dynamic. This will reduce the launch time of your app.
Find and remove unused code. You can use Periphery for that.
Inspect your .ipa to find any duplicated or unexpected assets
- First, make an archive an export the .ipa, if you don't know how to do it, check this question in stackoverflow
- Find the .ipa and change the extension to .zip, then unzip it
- Inspect it.
- Remove duplicate asstes from your assets catalog, or your bundles.
- Remove or exclude from "Release" files that don't contribute to the final version of the .ipa. For example README.md, JSON mockups, etc.
If you have string files (eg Localizables), remove the comments. Thanks uber-mahyar2 for the advice.

Build Settings to optimize size

Clang

Select your target > Build Setting > Apple Clang - Code generator > Optimization Level > Release > -Oz

Swift compiler configuration

Select your target > Build Setting > Swift Compiler - Code generator > Optimization Level > Release > -Osize
Select your target > Build Setting > Swift Compiler - Code generator > Compilation Moode > Release > Whole Module

Others

Select your target > Build Setting > Asset Catalog Compiler - Options > Optimization > Release > space
Select your target > Build Setting > Enable Testability > Release > No

CocoaPods

We should apply the above settings to all of our CocoaPods targets. Doing it manually will take forever, and they will be overwritten with every pod install

Add the following post_install at the end of your podfile to automatically apply the settings along with the pod install

post_install do |installer|
  installer.pods_project.targets.each do |target|
    target.build_configurations.each do |config|
      if config.name == 'Release'
        config.build_settings['SWIFT_OPTIMIZATION_LEVEL'] = '-Osize'
        config.build_settings['ASSETCATALOG_COMPILER_OPTIMIZATION'] = 'space'
        config.build_settings['GCC_OPTIMIZATION_LEVEL'] = 'z'
        config.build_settings['ENABLE_TESTABILITY'] = 'NO'
        config.build_settings['SWIFT_COMPILATION_MODE'] = 'wholemodule'
      end
    end
  end
end

If you want to move to static libraries use use_frameworks! :linkage => :static instead of use_frameworks

target 'YourTargertName' do
  use_frameworks! :linkage => :static
  # your pods
end

If you don't have at least CocoaPods 1.9.0, you will have to use use_modular_headers!

target 'YourTargertName' do
  use_modular_headers!
  # your pods
end