获取错误：EXC_BAD_INSTRUCTION（code = EXC_I386_INVOP，subcode = 0x0），为什么？

Question

我的代码如下：

let mvc = MainViewController() 
    let average = mvc.defaults.array(forKey: "grades") as! [Int] 
    let averagePoints = mvc.defaults.integer(forKey: "averagePoints") 
    gradePoints = averagePoints/average.count 

在最后一行，我得到一个EXC_BAD_INSTRUCTION（代码= EXC_I386_INVOP，子码=为0x0）的错误。这是什么意思，为什么我能得到它？

谢谢你的帮助！

Answer 1

尝试这种情况：

if let average = mvc.defaults.array(forKey: "grades") as? [Int], 
    let averagePoints = mvc.defaults.integer(forKey: "averagePoints") { 
    gradePoints = averagePoints/average.count 
} 

好像grades阵列或/和averagePoints是/是零。