Widget Families define the sizes your widget supports.
Each size gives you more space to show more information.

The 3 Main Sizes

.systemSmall   → 2x2 grid units  → one glanceable piece of info
.systemMedium  → 4x2 grid units  → current state + supporting info
.systemLarge   → 4x4 grid units  → full dashboard view

Declaring Support

.supportedFamilies([.systemSmall, .systemMedium, .systemLarge])

You decide which sizes to support.
If you only list .systemSmall → user can only add the small version.

Reading the Current Size

@Environment(\.widgetFamily) var family

WidgetKit injects the current family at runtime.
Use it to switch between different layouts.

From the Project

struct SampleWidgetEntryView: View {
    @Environment(\.widgetFamily) var family
    var entry: Provider.Entry

    var body: some View {
        switch family {
        case .systemSmall:  SmallWidgetView(entry: entry)
        case .systemMedium: MediumWidgetView(entry: entry)
        case .systemLarge:  LargeWidgetView(entry: entry)
        default:            SmallWidgetView(entry: entry)
        }
    }
}

One entry view → routes to three completely different layouts
Same data, different presentation per size

How Each Size Was Used in the Project

Small  → icon pill + main value + progress bar
         one focused piece of info

Medium → left: current session
         right: all 5 sessions with checkmarks
         split layout via Divider()

Large  → header + hero text + big icon
         progress bar with percentage
         full session list with icon circles + "Now" pill

The default Case

default: SmallWidgetView(entry: entry)

Required by Swift because widgetFamily has other cases
e.g. .systemExtraLarge, .accessoryCircular, .accessoryRectangular

If you don't handle them → fall back to small

Other Families You Can Support

.systemExtraLarge    → iPad only, very wide
.accessoryCircular   → lock screen / watch, circular
.accessoryRectangular→ lock screen, rectangular bar
.accessoryInline     → lock screen, single line of text

Mental Model