ios - 找不到成员(member)下标

Question

我正在尝试执行以下代码并收到错误 Could not find member 'subscript on Xcode6

var b:[[Float]] = [[1,2]]

var i2 = 0 // second to last control point
var pointIm1 = CGPoint(x: 0.0,y: 0.0)
var pointI = CGPoint(x: 0.0,y: 0.0)
var pointIp1 = CGPoint(x: 0.0,y: 0.0)
var px:Float = b[0][0] * Float(pointIm1.x) + b[0][0] * Float(pointI.x) + b[0][0] + b[0][0] * Float(pointIp1.x)

谁知道为什么会报错

编辑:有没有人有更好的主意，或者我需要像 Nate 在他的回答中建议的那样为每个下标创建不同的变量

//not looks good
var bj0 = b[j][0]
var bj1 = b[j][1]
var bj2 = b[j][2]
var bj3 = b[j][3]


var px:Float = bj0 * Float(pointIm1.x) + bj1 * Float(pointI.x) + bj2 + bj3 * Float(pointIp1.x)

Answer 1

这不是下标的问题 - Swift 在尝试解析较长的多项目表达式(如最后一行)时遇到麻烦。在 Playground 上我得到这个错误:

expression was too complex to be solved in reasonable time; consider breaking up the expression into distinct sub-expressions

您需要重构该行以克服此限制 - 例如:

let b00 = b[0][0]
var px: Float = b00 * Float(pointIm1.x) + b00 * Float(pointI.x) + b00 + b00 * Float(pointIp1.x)

---

你可以把它分成两步，像这样:

var px:Float = bj0 * Float(pointIm1.x) + bj1 * Float(pointI.x)
px += bj2 + bj3 * Float(pointIp1.x)