Updated for Xcode 14.0 beta 1
SwiftUI gives us both @Environment
and @EnvironmentObject
property wrappers, but they are subtly different: whereas @EnvironmentObject
allows us to inject arbitrary values into the environment, @Environment
is specifically there to work with SwiftUI’s own pre-defined keys.
For example, @Environment
is great for reading out things like a Core Data managed object context, whether the device is in dark mode or light mode, what size class your view is being rendered with, and more – fixed properties that come from the system. In code, it looks like this:
@Environment(\.horizontalSizeClass) var horizontalSizeClass
@Environment(\.managedObjectContext) var managedObjectContext
On the other hand, @EnvironmentObject
is designed for arbitrary objects to be read from the environment, like this:
@EnvironmentObject var order: Order
That difference might sound small, but it’s important because of the way @EnvironmentObject
is implemented. When we say that order
is of type Order
SwiftUI will look through its environment to find an object of that type and attach it to the order
property. However, when using @Environment
the same behavior isn’t possible, because many things might share the same data type.
For example:
@Environment(\.accessibilityReduceMotion) var reduceMotion
@Environment(\.accessibilityReduceTransparency) var reduceTransparency
@Environment(\.accessibilityEnabled) var accessibilityEnabled
All three of those environment keys return a Boolean, so without specifying exactly which key we mean it would be impossible to read them correctly.
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