Swift Combine - 观察 N 个对象数组内对象中的属性并与其他属性合并

Question

我正在为 iOS 构建一个图形应用程序。这是我的代码。

class Group {

    /// All the shapes contained in the group
    public var shapes: CurrentValueSubject<[Shape], Never>

    /// The frame of the group
    var frame: CurrentValueSubject<CGRect, Never>

    /// The path to be calculated and displayed to users from the contained shapes
    var cgPath: CurrentValueSubject<CGPath, Never>
}

class Shape {
    var path: CurrentValueSubject<Path, Never>  = .init(Path())
}

struct Path {
    public var points = [CGPoint]()
}

所以，这就是我想要做的，但不知道如何使用 Combine 来做。

我想让Group 观察它自己的frame、shapes 和它的形状的path（我需要合并所有这些），所以每次它们改变时，我都可以计算出新的要显示的 CGPath 并将其分配给 cgPath 属性（绘制所有内容的 View 将观察到该属性）。

请让我知道这是否可行，或者是否有更好的方法来解决所有这些问题。

提前致谢。

Answer 1

使用 CombineLatest

只需将@Published 属性包装器添加到您感兴趣的属性中。Combine 已经有一个预定义的CombineLatest3 方法来创建一个您可以订阅的Publisher。玩得开心。

import Foundation
import Combine
import CoreGraphics

class Group {

    init(shapes: [Shape], frame: CGRect, path: Path) {
        self.shapes = shapes
        self.frame = frame
        self.path = path
        self.observer = Publishers.CombineLatest3($shapes, $frame, $path)
            .sink(receiveCompletion: { _ in }, receiveValue: { (combined) in
                let (shapes, frame, path) = combined
                // do something
                print(shapes, frame, path)
            })
    }

    @Published var shapes: [Shape]
    @Published var frame: CGRect
    @Published var path: Path

    private var observer: AnyCancellable!
}

class Shape {
    var path: CurrentValueSubject<Path, Never>  = .init(Path())
}

struct Path {
    var points = [CGPoint]()
}

注意每次更改如何触发接收器关闭。

let group = Group(shapes: [Shape(), Shape()], frame: CGRect.zero, path: Path())
group.shapes = [Shape(), Shape(), Shape()]
group.frame = CGRect(x: 1, y: 1, width: 1, height: 1)
group.path.points = [CGPoint(x: 1, y: 1)]