Principle.md

Principle

In order to achieve the theme switching, the following five problems are mainly solved:

1. How to elegantly set theme properties

By extending the namespace property theme to the control, similar to the snp of SnapKit and the kf of Kingfisher, you can concentrate the properties that support the theme modification to the theme property. This is more elegant than directly extending the property 'theme_backgroundColor` to the control. The core code is as follows:

view.theme.backgroundColor = ThemeProvider({ (style) in
    If style == .dark {
        Return .white
    }else {
        Return .black
    }
})

2. How to configure the corresponding value according to the incoming style

Reference the iOS13 system API UIColor(dynamicProvider: <UITraitCollection) -> UIColor>). Customize the ThemeProvider structure, the initializer is init(_ provider: @escaping ThemePropertyProvider<T>). The passed argument ThemePropertyProvider is a closure defined as: typealias ThemePropertyProvider<T> = (ThemeStyle) -> T. This allows for maximum customization of different controls and different attribute configurations. The core code refers to the first step sample code.

3. How to save the theme properties configuration closure

Add the Associated object property providers to the control to store ThemeProvider. The core code is as follows:

Public extension ThemeWrapper where Base: UIView {
    Var backgroundColor: ThemeProvider<UIColor>? {
        Set(new) {
            If new != nil {
                Let baseItem = self.base
                Let config: ThemeCustomizationClosure = {[weak baseItem] (style) in
                    baseItem?.backgroundColor = new?.provider(style)
                }
                / / Stored in the extended properties provider
                Var newProvider = new
                newProvider?.config = config
                Self.base.providers["UIView.backgroundColor"] = newProvider
                ThemeManager.shared.addTrackedObject(self.base, addedConfig: config)
            }else {
                self.base.configs.removeValue(forKey: "UIView.backgroundColor")
            }
        }
        Get { return self.base.providers["UIView.backgroundColor"] as? ThemeProvider<UIColor> }
    }
}

4. How to track controls that support theme properties

In order to switch to the theme, notify the control that supports the theme property configuration. By tracking the target control when setting the theme properties. The core code is the code in step 3:

ThemeManager.shared.addTrackedObject(self.base, addedConfig: config)

5. How to switch the theme and call the closure of theme property

The theme is switched by ThemeManager.changeTheme(to: style), and the method internally calls the ThemeProvider.provider theme property in the providers of the tracked control to configure the closure. The core code is as follows:

Public func changeTheme(to style: ThemeStyle) {
    currentThemeStyle = style
    self.trackedHashTable.allObjects.forEach { (object) in
        If let view = object as? UIView {
            view.providers.values.forEach { self.resolveProvider($0) }
        }
    }
}
Private func resolveProvider(_ object: Any) {
    //castdown generic
    If let provider = object as? ThemeProvider<UIColor> {
        Provider.config?(currentThemeStyle)
    }else ...
}