ios - 对于 in 循环结果有时在 EXC_BAD_ACCESS

Question

有时我会在这段代码中遇到 EXC_BAD_ACCESS 错误:

internal func downloadMultiple(files: NSMutableArray, remoteBaseUrl: NSURL, completion: (result: Int)->()) -> Void {
    self.filesToDownload = files
    self.cb = completion

    for item in files { // this line gets marked, but why this line?
        print("file ", item["file"] as! String)
        self.download(remoteBaseUrl.URLByAppendingPathComponent(item["file"] as! String)!)
    }
}

但它只是偶尔发生，知道如何找出造成这种情况的原因吗？

Answer 1

你遇到崩溃是因为 item[file] 是 nil 并且你正在使用强制展开，像这样使用可选绑定(bind)

for item in files { 
    // this line gets marked, but why this line?
    if let file = item["file"] as String {
        print("file ", file)
        self.download(remoteBaseUrl.URLByAppendingPathComponent(file)
    } else {
        print("file not available")
    }

}