在 Swift 中，我试图在 0 和 1 之间获得一个随机浮点数，但我似乎无法让类型转换起作用。
func randomCGFloat() -> CGFloat {
return CGFloat(arc4random()) / UINT32_MAX
}
我收到“CGFloat”不可转换为“UInt8”错误
运行 Xcode 6。
【问题讨论】：
标签： swift random arc4random cgfloat
这是Int、Double、Float、CGFloat
的随机数的扩展Swift 3 & 4 & 5 语法
import Foundation
import CoreGraphics
// MARK: Int Extension
public extension Int {
/// Returns a random Int point number between 0 and Int.max.
static var random: Int {
return Int.random(n: Int.max)
}
/// Random integer between 0 and n-1.
///
/// - Parameter n: Interval max
/// - Returns: Returns a random Int point number between 0 and n max
static func random(n: Int) -> Int {
return Int(arc4random_uniform(UInt32(n)))
}
/// Random integer between min and max
///
/// - Parameters:
/// - min: Interval minimun
/// - max: Interval max
/// - Returns: Returns a random Int point number between 0 and n max
static func random(min: Int, max: Int) -> Int {
return Int.random(n: max - min + 1) + min
}
}
// MARK: Double Extension
public extension Double {
/// Returns a random floating point number between 0.0 and 1.0, inclusive.
static var random: Double {
return Double(arc4random()) / 0xFFFFFFFF
}
/// Random double between 0 and n-1.
///
/// - Parameter n: Interval max
/// - Returns: Returns a random double point number between 0 and n max
static func random(min: Double, max: Double) -> Double {
return Double.random * (max - min) + min
}
}
// MARK: Float Extension
public extension Float {
/// Returns a random floating point number between 0.0 and 1.0, inclusive.
static var random: Float {
return Float(arc4random()) / 0xFFFFFFFF
}
/// Random float between 0 and n-1.
///
/// - Parameter n: Interval max
/// - Returns: Returns a random float point number between 0 and n max
static func random(min: Float, max: Float) -> Float {
return Float.random * (max - min) + min
}
}
// MARK: CGFloat Extension
public extension CGFloat {
/// Randomly returns either 1.0 or -1.0.
static var randomSign: CGFloat {
return (arc4random_uniform(2) == 0) ? 1.0 : -1.0
}
/// Returns a random floating point number between 0.0 and 1.0, inclusive.
static var random: CGFloat {
return CGFloat(Float.random)
}
/// Random CGFloat between 0 and n-1.
///
/// - Parameter n: Interval max
/// - Returns: Returns a random CGFloat point number between 0 and n max
static func random(min: CGFloat, max: CGFloat) -> CGFloat {
return CGFloat.random * (max - min) + min
}
}
使用：
let randomNumDouble = Double.random(min: 0.00, max: 23.50)
let randomNumInt = Int.random(min: 56, max: 992)
let randomNumFloat = Float.random(min: 6.98, max: 923.09)
let randomNumCGFloat = CGFloat.random(min: 6.98, max: 923.09)
【讨论】：
return Float(arc4random()) / 0xFFFFFFFF 行现在会发出警告：'4294967295' is not exactly representable as 'Float'; it becomes '4294967296'。知道如何解决该警告吗？我正在考虑除以Float(UInt32.max)。
斯威夫特 5
let randomFloat = CGFloat.random(in: 0...1)
【讨论】：
为 Swift 3 更新 Sandy Chapman's answer：
extension ClosedRange where Bound : FloatingPoint {
public func random() -> Bound {
let range = self.upperBound - self.lowerBound
let randomValue = (Bound(arc4random_uniform(UINT32_MAX)) / Bound(UINT32_MAX)) * range + self.lowerBound
return randomValue
}
}
现在你可以说像(-1.0...1.0).random() 这样的东西了。
编辑我认为今天（Swift 4）我会这样写：
extension ClosedRange where Bound : FloatingPoint {
public func random() -> Bound {
let max = UInt32.max
return
Bound(arc4random_uniform(max)) /
Bound(max) *
(upperBound - lowerBound) +
lowerBound
}
}
注意 Swift 4.2 引入了本机随机数生成，所有这些都变得毫无意义。
【讨论】：
swift 4.2：
let randomFloat = Float.random(in: 0..<1)
【讨论】：
drand48()
如果你需要[双]。介于 0 和 1 之间。仅此而已。
【讨论】：
Xcode：9.2，斯威夫特 4
extension BinaryInteger {
static func rand(_ min: Self, _ max: Self) -> Self {
let _min = min
let difference = max+1 - _min
return Self(arc4random_uniform(UInt32(difference))) + _min
}
}
extension BinaryFloatingPoint {
private func toInt() -> Int {
// https://stackoverflow.com/q/49325962/4488252
if let value = self as? CGFloat {
return Int(value)
}
return Int(self)
}
static func rand(_ min: Self, _ max: Self, precision: Int) -> Self {
if precision == 0 {
let min = min.rounded(.down).toInt()
let max = max.rounded(.down).toInt()
return Self(Int.rand(min, max))
}
let delta = max - min
let maxFloatPart = Self(pow(10.0, Double(precision)))
let maxIntegerPart = (delta * maxFloatPart).rounded(.down).toInt()
let randomValue = Int.rand(0, maxIntegerPart)
let result = min + Self(randomValue)/maxFloatPart
return Self((result*maxFloatPart).toInt())/maxFloatPart
}
}
print("\(Int.rand(1, 20))")
print("\(Float.rand(5.231233, 44.5, precision: 3))")
print("\(Double.rand(5.231233, 44.5, precision: 4))")
print("\(CGFloat.rand(5.231233, 44.5, precision: 6))")
import Foundation
import CoreGraphics
func run() {
let min = 2.38945
let max = 2.39865
for _ in 0...100 {
let precision = Int.rand(0, 5)
print("Precision: \(precision)")
floatSample(min: Float(min), max: Float(max), precision: precision)
floatSample(min: Double(min), max: Double(max), precision: precision)
floatSample(min: CGFloat(min), max: CGFloat(max), precision: precision)
intSample(min: Int(1), max: Int(10000))
print("")
}
}
private func printResult<T: Comparable>(min: T, max: T, random: T) {
let result = "\(T.self) rand[\(min), \(max)] = \(random)"
print(result)
}
func floatSample<T: BinaryFloatingPoint>(min: T, max: T, precision: Int) {
printResult(min: min, max: max, random: T.rand(min, max, precision: precision))
}
func intSample<T: BinaryInteger>(min: T, max: T) {
printResult(min: min, max: max, random: T.rand(min, max))
}
【讨论】：
基于 YannickSteph 的回答
要使其适用于任何浮点类型，例如Double、Float、CGFloat 等，您可以为BinaryFloatingPoint 类型进行扩展：
extension BinaryFloatingPoint {
/// Returns a random floating point number between 0.0 and 1.0, inclusive.
public static var random: Self {
return Self(arc4random()) / 0xFFFFFFFF
}
/// Random double between 0 and n-1.
///
/// - Parameter n: Interval max
/// - Returns: Returns a random double point number between 0 and n max
public static func random(min: Self, max: Self) -> Self {
return Self.random * (max - min) + min
}
}
【讨论】：
这里的框架在 Swift 中生成随机数数据方面做得很好： https://github.com/thellimist/SwiftRandom/blob/master/SwiftRandom/Randoms.swift
public extension Int {
/// SwiftRandom extension
public static func random(lower: Int = 0, _ upper: Int = 100) -> Int {
return lower + Int(arc4random_uniform(UInt32(upper - lower + 1)))
}
}
public extension Double {
/// SwiftRandom extension
public static func random(lower: Double = 0, _ upper: Double = 100) -> Double {
return (Double(arc4random()) / 0xFFFFFFFF) * (upper - lower) + lower
}
}
public extension Float {
/// SwiftRandom extension
public static func random(lower: Float = 0, _ upper: Float = 100) -> Float {
return (Float(arc4random()) / 0xFFFFFFFF) * (upper - lower) + lower
}
}
public extension CGFloat {
/// SwiftRandom extension
public static func random(lower: CGFloat = 0, _ upper: CGFloat = 1) -> CGFloat {
return CGFloat(Float(arc4random()) / Float(UINT32_MAX)) * (upper - lower) + lower
}
}
【讨论】：
Generic iOS device 编译时不起作用。 0xffffffff 不适合 Int。试试这个 CGFloat(UInt32.max)
下面是 IntervalType 类型的扩展：
extension IntervalType {
public func random() -> Bound {
let range = (self.end as! Double) - (self.start as! Double)
let randomValue = (Double(arc4random_uniform(UINT32_MAX)) / Double(UINT32_MAX)) * range + (self.start as! Double)
return randomValue as! Bound
}
}
使用此扩展，您可以使用区间语法生成区间，然后在该区间中获取随机值：
(0.0...1.0).random()
加法
如果您希望为Ints 做同样的事情，那么您可以在CollectionType 协议上使用以下扩展：
extension CollectionType {
public func random() -> Self._Element {
if let startIndex = self.startIndex as? Int {
let start = UInt32(startIndex)
let end = UInt32(self.endIndex as! Int)
return self[Int(arc4random_uniform(end - start) + start) as! Self.Index]
}
var generator = self.generate()
var count = arc4random_uniform(UInt32(self.count as! Int))
while count > 0 {
generator.next()
count = count - 1
}
return generator.next() as! Self._Element
}
}
Ints 不要使用IntervalType。他们改用Range。对 CollectionType 类型执行此操作的好处是它会自动转移到 Dictionary 和 Array 类型。
例子：
(0...10).random() // Ex: 6
["A", "B", "C"].random() // Ex: "B"
["X":1, "Y":2, "Z":3].random() // Ex: (.0: "Y", .1: 2)
【讨论】：
jmduke 的建议似乎可以在 Playground 中使用，只是对功能稍作改动：
func randomCGFloat() -> Float {
return Float(arc4random()) / Float(UInt32.max)
}
以及从swift doc和drawag中指出的原因：类型转换必须是显式的，文档中的示例是：
let three = 3
let pointOneFourOneFiveNine = 0.14159
let pi = Double(three) + pointOneFourOneFiveNine
// pi equals 3.14159, and is inferred to be of type Double
【讨论】：
尝试将除数也初始化为浮点数，a la：
CGFloat(Float(arc4random()) / Float(UINT32_MAX))
【讨论】：
Float——只需CGFloat(arc4random()) / CGFloat(UInt32.max)。