对于循环的结果有时EXC_BAD_ACCESS

Question

有时我得到一个EXC_BAD_ACCESS错误在此代码：

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)!) 
    } 
} 

但它只是有时会发生，任何想法如何找出是什么原因造成的？

Answer 1

你所得到的崩溃，因为item[file]是nil和你正在使用武力展开，一起去选购这样

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") 
    } 

}