如何在 Swift 中解決轉義閉包捕獲“inout”參數？

Question

我想用一個函數更新一個狀態值，在這個函數中我想使用一個DispatchQueue但我收到這個錯誤：

Escaping closure captures 'inout' parameter 'currentValue'

我該如何解決這個問題？

struct ContentView: View {
    
    @State private var offset: CGFloat = CGFloat()
    
    var body: some View {
        
        Color.yellow
            .overlay(
                
                Circle()
                    .fill(Color.red)
                    .frame(width: 100.0, height: 100.0, alignment: .center)
                    .offset(y: offset)
                
            )
            .overlay(
                
                Button("update") {
                    
                    updater(currentValue: &offset, goalValue: 300.0)
                    
                }
                .font(Font.body.bold())
                .padding()
                
                , alignment: .bottom)
        
    }
    
}

---

func updater(currentValue: inout CGFloat, goalValue: CGFloat) {
    
    if (currentValue + 1.0) <= goalValue {
        
        currentValue += 1.0
        
        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + DispatchTimeInterval.milliseconds(1000)) {

            updater(currentValue: &currentValue, goalValue: goalValue)

        }
        
    }
    
}

Answer 1

您可以通過創建一個額外的變量來修復您的錯誤。 像這樣

func updater(currentValue: inout CGFloat, goalValue: CGFloat) {
        var currentValue = currentValue // <--- Here
        if (currentValue + 1.0) <= goalValue {
            
            currentValue += 1.0
            
            DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + DispatchTimeInterval.milliseconds(1000)) {
                updater(currentValue: &currentValue, goalValue: goalValue)
            }
        }
    }

但是通過這樣做，您的視圖無法更新。 您可以通過此修改您的代碼

struct ContentView: View {
    
    @State private var offset: CGFloat = CGFloat()
    
    var body: some View {
        
        Color.yellow
            .overlay(
                
                Circle()
                    .fill(Color.red)
                    .frame(width: 100.0, height: 100.0, alignment: .center)
                    .offset(y: offset)
                
            )
            .overlay(
                
                Button("update") {
                    
                    updater(goalValue: 300.0)
                    
                }
                .font(Font.body.bold())
                .padding()
                
                , alignment: .bottom)
        
    }
    
    func updater(goalValue: CGFloat) {
        if (offset + 1.0) <= goalValue {
            
            offset += 1.0
            
            DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + DispatchTimeInterval.milliseconds(1000)) {
                updater(goalValue: goalValue)
            }
        }
    }
}