如何用 combine 观察数组的新值？

Question

如果我有一个数组：

var arr = [0,1,2]

以及它的 Combine 发布者：

arr.publisher
    .sink { completion in print("Completed with \(completion)")
    } receiveValue: { val in
        print("Received value \(val)")
    }
arr.append(3)

为什么它立即结束：

Received value 0
Received value 1
Received value 2
Completed with finished

如何让 Combine 每次向数组追加值时都执行代码？

Answer 1

数组的 publisher 方法正是这样做的 - 发出数组的每个元素然后完成，因为调用发布者时数组的元素数量是有限的。

如果您希望每次数组更改时都收到通知（不仅仅是在附加内容时，而是在任何更改时），请为数组创建一个 @Published var 并将观察器附加到它：

@Published var arr = [1,2,3]

cancellable = $arr
    .sink { completion in print("Completed with \(completion)")
    } receiveValue: { val in
        print("Received value \(val)")
    }

arr.append(4)

输出将是：

Received value [1, 2, 3]
Received value [1, 2, 3, 4]

但看起来您真正想要的是收听一次一个发出的数字流。然后定义一个那个类型的@Published var，听听。每次 var 更改时都会调用您：

@Published var value = 1

cancellable = $value
    .sink { completion in print("Completed with \(completion)")
    } receiveValue: { val in
        print("Received value \(val)")
    }

value = 2
value = 3
value = 4

输出将是：

Received value 1
Received value 2
Received value 3
Received value 4

如何用 combine 观察数组的新值？

How to observe array's new values with combine?

swift

combine