“不能在属性初始化器中使用实例成员“缓解”;属性初始化器在可用的“自我”之前运行

Question

var allEvents: [String] = ["SOUTHERN STATES PASS LAWS TO DISENFRANCISE BLACKS", "THEODORE ROOSEVELT ELECTED VICE PRESIDENT", "WRIGHT BROTHERS FIRST FLIGHT", "SAN FRANCISCO EARTHQUAKE", "FORD INTRODUCES MODEL T", "WORLD WAR I BEGINS IN EUROPE", "WORLD WAR I ENDS", "TR DIES – CARNEGIE DIES", "GERMAN MONEY HYPER INFLATES", "TREATY OF VERSAILLES, 19TH AMENDMENT", "HINDENBURG ELECTED PRESIDENT OF GERMANY", "STOCK MARKET CRASHES, DEPRESSION BEGINS", "HITLER’S NAZI PARTY GAINS MAJORITY IN PARLIAMENT", "HITLER BEGINS TO TAKE POWER IN GERMANY", "FRANKLIN ROOSEVELT ELECTED PRESIDENT", "FDR INAUGURATED “100 DAYS”", "HINDENBURG DIES, HITLER APPOINTS HIMSELF PRESIDENT  -  “ FUEHRER”", "FDR RE-ELECTED", "German airship HINDENBURG BURNS IN NEW JERSEY", "“MUNICH” – British P.M. Chamberlain agrees that Hitler can have Czechoslovakia.", "Germany invades Holland, Belgium and France – Churchill becomes P.M.", "Germany invades Russia", "JAPANESE ATTACK PEARL HARBOR – U.S. DECLARES WAR ON JAPAN", "HITLER DECLARES WAR ON U.S."]
var eventIndex1: Int = 0
var eventIndex2: Int = 0
var eventIndex3: Int = 0
var eventIndex4: Int = 0
func generateRandomIndex() -> [Int] {
    while (eventIndex1 == eventIndex2) && (eventIndex2 == eventIndex3) && (eventIndex1 == eventIndex3) && (eventIndex1 == eventIndex4) && (eventIndex2 == eventIndex4) && (eventIndex3 == eventIndex4) {
        eventIndex1 = GKRandomSource.sharedRandom().nextInt(upperBound: allEvents.count)
        eventIndex2 = GKRandomSource.sharedRandom().nextInt(upperBound: allEvents.count)
        eventIndex3 = GKRandomSource.sharedRandom().nextInt(upperBound: allEvents.count)
        eventIndex4 = GKRandomSource.sharedRandom().nextInt(upperBound: allEvents.count)
    }
    return [eventIndex1, eventIndex2, eventIndex3, eventIndex4]
}
var eventIndexes = generateRandomIndex()
var index1 = eventIndexes[0]
var index2 = eventIndexes[1]
var index3 = eventIndexes[2]
var index4 = eventIndexes[3]
var event1 = allEvents[index1]
var event2 = allEvents[index2]
var event3 = allEvents[index3]
var event4 = allEvents[index4]

上面的以下代码基本上是使用该函数应该生成的无缩写随机索引从促进阵列中拉出的。除每个事件变量外，在属性初始化器中都有一个"无法使用实例成员"的"缓解"；属性初始化器在"自我"可用之前运行。有什么建议么？不知道如何修复。

Answer 1

您不能初始化具有另一个属性值的标准属性（并且没有保证将按照您假设将是的方式在源代码顺序中初始化它们）。您可以初始化具有另一个值的lazy属性，但对于此问题而言，这太复杂了。访问对象的属性需要初始化整个对象，并且在设置所有属性之前都不会初始化。

这种逻辑最好在init中完成。这是我自己写的方式（随着洗牌扩展）：

class ViewController {
    //There's just one of these in the world, not one per class. And I can't
    // imagine it changing (so should be let)
    static let allEvents = ["SOUTHERN STATES PASS LAWS TO DISENFRANCISE BLACKS", "THEODORE ROOSEVELT ELECTED VICE PRESIDENT", "WRIGHT BROTHERS FIRST FLIGHT", "SAN FRANCISCO EARTHQUAKE", "FORD INTRODUCES MODEL T", "WORLD WAR I BEGINS IN EUROPE", "WORLD WAR I ENDS", "TR DIES – CARNEGIE DIES", "GERMAN MONEY HYPER INFLATES", "TREATY OF VERSAILLES, 19TH AMENDMENT", "HINDENBURG ELECTED PRESIDENT OF GERMANY", "STOCK MARKET CRASHES, DEPRESSION BEGINS", "HITLER’S NAZI PARTY GAINS MAJORITY IN PARLIAMENT", "HITLER BEGINS TO TAKE POWER IN GERMANY", "FRANKLIN ROOSEVELT ELECTED PRESIDENT", "FDR INAUGURATED “100 DAYS”", "HINDENBURG DIES, HITLER APPOINTS HIMSELF PRESIDENT  -  “ FUEHRER”", "FDR RE-ELECTED", "German airship HINDENBURG BURNS IN NEW JERSEY", "“MUNICH” – British P.M. Chamberlain agrees that Hitler can have Czechoslovakia.", "Germany invades Holland, Belgium and France – Churchill becomes P.M.", "Germany invades Russia", "JAPANESE ATTACK PEARL HARBOR – U.S. DECLARES WAR ON JAPAN", "HITLER DECLARES WAR ON U.S."]
    // Do you really need both of these? If so, I'd probably actually just keep
    // eventIndices and compute events when needed, but if you access it a lot,
    // this is fine. But "event1" "event2" etc is bad practice
    let eventIndices: [Int]
    let events: [String]
    init() {
        eventIndices = Array(ViewController.allEvents.indices.shuffled().prefix(4))
        events = eventIndices.map { ViewController.allEvents[$0] }
    }
}

好吧，这就是我的方式，但是如果我们想以您的风格保持它，我们仍然可以做到这一点。但是，您仍然需要allEvents为static。

class ViewController {
    static let allEvents: [String] = ["SOUTHERN STATES PASS LAWS TO DISENFRANCISE BLACKS", "THEODORE ROOSEVELT ELECTED VICE PRESIDENT", "WRIGHT BROTHERS FIRST FLIGHT", "SAN FRANCISCO EARTHQUAKE", "FORD INTRODUCES MODEL T", "WORLD WAR I BEGINS IN EUROPE", "WORLD WAR I ENDS", "TR DIES – CARNEGIE DIES", "GERMAN MONEY HYPER INFLATES", "TREATY OF VERSAILLES, 19TH AMENDMENT", "HINDENBURG ELECTED PRESIDENT OF GERMANY", "STOCK MARKET CRASHES, DEPRESSION BEGINS", "HITLER’S NAZI PARTY GAINS MAJORITY IN PARLIAMENT", "HITLER BEGINS TO TAKE POWER IN GERMANY", "FRANKLIN ROOSEVELT ELECTED PRESIDENT", "FDR INAUGURATED “100 DAYS”", "HINDENBURG DIES, HITLER APPOINTS HIMSELF PRESIDENT  -  “ FUEHRER”", "FDR RE-ELECTED", "German airship HINDENBURG BURNS IN NEW JERSEY", "“MUNICH” – British P.M. Chamberlain agrees that Hitler can have Czechoslovakia.", "Germany invades Holland, Belgium and France – Churchill becomes P.M.", "Germany invades Russia", "JAPANESE ATTACK PEARL HARBOR – U.S. DECLARES WAR ON JAPAN", "HITLER DECLARES WAR ON U.S."]
    static func generateRandomIndex() -> [Int] {
        var eventIndex1: Int = 0
        var eventIndex2: Int = 0
        var eventIndex3: Int = 0
        var eventIndex4: Int = 0
        while (eventIndex1 == eventIndex2) || (eventIndex2 == eventIndex3) || (eventIndex1 == eventIndex3) || (eventIndex1 == eventIndex4) || (eventIndex2 == eventIndex4) || (eventIndex3 == eventIndex4) {
            eventIndex1 = GKRandomSource.sharedRandom().nextInt(upperBound: allEvents.count)
            eventIndex2 = GKRandomSource.sharedRandom().nextInt(upperBound: allEvents.count)
            eventIndex3 = GKRandomSource.sharedRandom().nextInt(upperBound: allEvents.count)
            eventIndex4 = GKRandomSource.sharedRandom().nextInt(upperBound: allEvents.count)
        }
        return [eventIndex1, eventIndex2, eventIndex3, eventIndex4]
    }
    let index1: Int
    let index2: Int
    let index3: Int
    let index4: Int
    let event1: String
    let event2: String
    let event3: String
    let event4: String
    init() {
        let eventIndexes = ViewController.generateRandomIndex()
        index1 = eventIndexes[0]
        index2 = eventIndexes[1]
        index3 = eventIndexes[2]
        index4 = eventIndexes[3]
        event1 = ViewController.allEvents[index1]
        event2 = ViewController.allEvents[index2]
        event3 = ViewController.allEvents[index3]
        event4 = ViewController.allEvents[index4]
    }
}

如果不需要在此文件之外看到allEvents，则可以通过将其吊起以文件范围来简单：

fileprivate let allEvents: [String] = ["SOUTHERN STATES PASS LAWS TO DISENFRANCISE BLACKS", "THEODORE ROOSEVELT ELECTED VICE PRESIDENT", "WRIGHT BROTHERS FIRST FLIGHT", "SAN FRANCISCO EARTHQUAKE", "FORD INTRODUCES MODEL T", "WORLD WAR I BEGINS IN EUROPE", "WORLD WAR I ENDS", "TR DIES – CARNEGIE DIES", "GERMAN MONEY HYPER INFLATES", "TREATY OF VERSAILLES, 19TH AMENDMENT", "HINDENBURG ELECTED PRESIDENT OF GERMANY", "STOCK MARKET CRASHES, DEPRESSION BEGINS", "HITLER’S NAZI PARTY GAINS MAJORITY IN PARLIAMENT", "HITLER BEGINS TO TAKE POWER IN GERMANY", "FRANKLIN ROOSEVELT ELECTED PRESIDENT", "FDR INAUGURATED “100 DAYS”", "HINDENBURG DIES, HITLER APPOINTS HIMSELF PRESIDENT  -  “ FUEHRER”", "FDR RE-ELECTED", "German airship HINDENBURG BURNS IN NEW JERSEY", "“MUNICH” – British P.M. Chamberlain agrees that Hitler can have Czechoslovakia.", "Germany invades Holland, Belgium and France – Churchill becomes P.M.", "Germany invades Russia", "JAPANESE ATTACK PEARL HARBOR – U.S. DECLARES WAR ON JAPAN", "HITLER DECLARES WAR ON U.S."]
class ViewController {
    ...
        event1 = allEvents[index1]
        event2 = allEvents[index2]
        event3 = allEvents[index3]
        event4 = allEvents[index4]
    ...

但是，所有这些的关键课程是您在初始化对象之前无法访问对象中的属性。