🔰flexible column

SwiftUI ⟩ Layout ⟩ Grids ⟩ flexible column

💈範例

雖然本範例的兩個欄位都是 flexible columen 有且最小寬度 minimum 屬性分別為 50, 120：

let columns = [
    GridItem(.flexible(minimum: 50)),    // ⭐ flexible
    GridItem(.flexible(minimum: 120))    // ⭐ flexible
]

但真正跑出來的欄位寬度，卻超乎我們的想像。

final layout

2 passes

screenshot

⬆️ 需要： 👔 VGridForEach

struct ContentView: View {
    
    let columns = [
        GridItem(.flexible(minimum: 50)),    // ⭐ flexible
        GridItem(.flexible(minimum: 120))    // ⭐ flexible
    ]
    
    var body: some View {
        grid(columns)
    }
}

extension ContentView {
    
    /// a grid of swatches
    func grid(_ columns: [GridItem]) -> some View {
        // 👔 VGridForEach
        VGridForEach(0..<6, columns: columns){ 
            numberSwatch($0)
        }
        .frame(width: 200)        // grid width = scroll view width ⭐ 
        .border(Color.yellow)     // scroll view border (yellow)
        .padding()
        .border(Color.blue)       // padding border (blue)
        .frame(height: 300)
    }
    
    /// a color swatch with a number on it
    @ViewBuilder func numberSwatch(_ i: Int) -> some View {
        let color: Color = i % 2 == 0 ? .green : .pink
        color
            .opacity(0.5)
            .frame(height: 40)
            .overlay(Text("\(i)").font(.title))
    }
}

欄位寬度的計算方式：👉 grid layout algorithm

// initial values
r = 200    // remaining width (intial = grid width)
n = 2      // # of remaining cols

// r -= (fixed widths) + (spacing between cols)
r -= 8     // 192

// 1st col width
w1 = clamp(r/n)     // 192/2 = 96
   = 96             // clamped to [50, .inf)

// update r, n
r -= w1             // 192 - 96 = 96
n -= 1              // 1

// 2nd col width
w2 = clamp(r/n)      // 96/1 = 96
   = 120             // clamped to [120, .inf) ⭐

// overall width
W = 96 + 8 + 120
  = 224               // larger than original (200) ⭐
                      // frame stretched out 12 pts both sides
                      
// ----------------------------
//     2nd (rendering) pass 
// ----------------------------

r = W     // 224: start with overall width
n = 2     // # of remaining cols

// r -= (fixed widths) + (spacing between cols)
r -= 8             // 216

// 1st col width
w1 = clamp(r/n)    // 216/2 = 108
   = 108           // clamped to [50, .inf)
   
// update r, n
r -= w1            // 108
n -= 1             // 1

// 2nd col width
w2 = clamp(r/n)     // 108/1 = 108
   = 120            // clamped to [120, .inf)
   
// overall width
W = 108 + 8 + 120    // final layout ⭐
  = 236              // grid appears out of center by 6 pts ⭐

📘 手冊

• SwiftUI ⟩ Layout ⟩ LazyVGrid ⟩ .init(columns:alignment: ...)

📗 參考

• objc ⟩ SwiftUI’s Grid Views ⭐️⭐️ - how flexible/adaptive columns behave. (💈例一)

👥 相關

• grid layout algorithm

• adaptive column