Promise
Promise 创建时实例化action实例， filfull, reject 两个闭包是action的两个入参，主要是负责succ和fail的处理，action是把filfull, reject合并后，通过then函数处理。
then函数是Promise内部函数，可以action中filfull，reject中的值处理后，再通过Promise包装返回，形成一个调用链。
// then 处理
func then<U>(exec: @escaping (T) -> Promise<U>?) -> Promise<U> {
return Promise<U>{ [unowned self] (resolve, reject) in
let c1:fulfilled = { v in
exec(v)?.doExec(callback: { (obj) in
resolve(obj)
})
}
let c2:rejected = { e in
reject(e)
}
self.executor(c1, c2)
}
}
处理Promise结果时，可以通过then获取上次Promise对象的action中携带的值，然后实例化 fulfilledCallback，rejectedCallback接受返回成功值，后者异常值
// 处理fail
func doCatch(callback: @escaping rejected) {
rejectedCallback = callback
let c1:fulfilled = { _ in }
let c2:rejected = { [unowned self] err in
self.reject(err: err)
}
executor(c1, c2)
}
完整实现
class Promise<T> {
typealias fulfilled = (T) -> Void
typealias rejected = (Error) -> Void
typealias action = (@escaping fulfilled,@escaping rejected) -> Void
// 实例化执行器
private let executor:action
// 成功回调
private var fulfilledCallback:fulfilled?
// 异常回调
private var rejectedCallback:rejected?
init(exec:@escaping action) {
executor = exec
}
// 处理成功结果
private func resolve(result: T) {
if fulfilledCallback == nil {
return
}
fulfilledCallback!(result)
}
// 处理异常结果
private func reject(err:Error) {
if rejectedCallback == nil {
return
}
rejectedCallback!(err)
}
// 处理succ
func doExec(callback:@escaping fulfilled) {
fulfilledCallback = callback
let c1:fulfilled = { [unowned self] v in
self.resolve(result: v)
}
let c2:rejected = { _ in }
executor(c1, c2)
}
// 处理fail
func doCatch(callback: @escaping rejected) {
rejectedCallback = callback
let c1:fulfilled = { _ in }
let c2:rejected = { [unowned self] err in
self.reject(err: err)
}
executor(c1, c2)
}
// then 处理
func then<U>(exec: @escaping (T) -> Promise<U>?) -> Promise<U> {
return Promise<U>{ [unowned self] (resolve, reject) in
let c1:fulfilled = { v in
exec(v)?.doExec(callback: { (obj) in
resolve(obj)
})
}
let c2:rejected = { e in
reject(e)
}
self.executor(c1, c2)
}
}
}
测试
// fun1
func getStr(pwd:String? = nil) -> Promise<String> {
// exec pwd
let v = Promise<String>.init { (fulfill, reject) in
let v1 = Int(arc4random())%100 > 10 ? true : false
if v1 {
fulfill("true")
} else {
reject(MyErr.net)
}
}
return v
}
// fun2
func getInt(value:String? = nil) -> Promise<Int> {
// exec value
let v = Promise<Int>.init { (fulfill, reject) in
fulfill(0)
}
return v
}
getStr().then { (v) -> Promise<Int>? in
return getInt(value: v)
}.doExec { (v) in
print(v)
}
