UICollectionView崩潰下載時圖像

Question

斯威夫特4： 我得到一個錯誤約

「意外發現零而展開的可選值」

和斷點是我downloadImage而我從JSON查詢中填入UICollectionView。

有關我如何使這更安全的任何建議？還是我看錯了東西？ 這裏是downloadImage代碼：

extension UIImageView { 
    @objc func downloadImage(from url: String){ 
     let urlRequest = URLRequest(url: URL(string: url)!) 
     let task = URLSession.shared.dataTask(with: urlRequest) { (data, response, error) in 

      if error != nil { 
       print(error as Any) 
       return 
      } 
      DispatchQueue.main.async { 
       if UIImage(data: data!) != nil { 
       self.image = UIImage(data: data!) 
       } 
      } 

     } 
     task.resume() 

    } 

這裏是函數填充的CollectionView它打破：

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell { 

     let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "articleCell", for: indexPath) as! ArticleCell 

     cell.title.text = self.articles?[indexPath.item].headline 

//這裏崩潰

cell.imgView.downloadImage(from: (self.articles?[indexPath.item].imageURL!)!) 

    cell.contentView.layer.cornerRadius = 0.5 
    cell.contentView.layer.borderWidth = 1.0 

    cell.contentView.layer.borderColor = UIColor.clear.cgColor 
    cell.contentView.layer.masksToBounds = true 

    cell.layer.shadowColor = UIColor.gray.cgColor 
    cell.layer.shadowOffset = CGSize(width: 0, height: 0.5) 
    cell.layer.shadowRadius = 1 
    cell.layer.shadowOpacity = 0.5 
    cell.layer.masksToBounds = false 
    cell.layer.shadowPath = UIBezierPath(roundedRect:cell.bounds, cornerRadius:cell.contentView.layer.cornerRadius).cgPath 


    return cell 


} 

這裏是控制檯輸出：

2017-12-18 06:55:08.412546+0100 Keyboard[81355:4788284] Failed to inherit CoreMedia permissions from 81260: (null) 
2017-12-18 06:55:08.634498+0100 Keyboard[81355:4788188] [MC] Lazy loading NSBundle MobileCoreServices.framework 
2017-12-18 06:55:08.635348+0100 Keyboard[81355:4788188] [MC] Loaded MobileCoreServices.framework 
2017-12-18 06:55:08.637140+0100 Keyboard[81355:4788188] [MC] System group container for systemgroup.com.apple.configurationprofiles path is /Users/me/Library/Developer/CoreSimulator/Devices/9BAC6166-3559-4962-9715-F388A162E95F/data/Containers/Shared/SystemGroup/systemgroup.com.apple.configurationprofiles 
Category: business 
true 
Fatal error: Unexpectedly found nil while unwrapping an Optional value 
2017-12-18 06:55:11.138236+0100 Keyboard[81355:4788188] Fatal error: Unexpectedly found nil while unwrapping an Optional value 
(lldb) 

這裏是調試：

libswiftCore.dylib`function signature specialization <preserving fragile attribute, Arg[2] = Dead, Arg[3] = Dead> of Swift._fatalErrorMessage(Swift.StaticString, Swift.StaticString, file: Swift.StaticString, line: Swift.UInt, flags: Swift.UInt32) -> Swift.Never: 
    0x113a5e420 <+0>: pushq %rbp 
    0x113a5e421 <+1>: movq %rsp, %rbp 
    0x113a5e424 <+4>: pushq %r15 
    0x113a5e426 <+6>: pushq %r14 
    0x113a5e428 <+8>: pushq %r13 
    0x113a5e42a <+10>: pushq %r12 
    0x113a5e42c <+12>: pushq %rbx 
    0x113a5e42d <+13>: pushq %rax 
    0x113a5e42e <+14>: movl %r9d, %r14d 
    0x113a5e431 <+17>: movq %r8, %r15 
    0x113a5e434 <+20>: movq %rcx, %rbx 
    0x113a5e437 <+23>: movl %edx, -0x2c(%rbp) 
    0x113a5e43a <+26>: movq %rsi, %r13 
    0x113a5e43d <+29>: movq %rdi, %r12 
    0x113a5e440 <+32>: leaq 0x1c6551(%rip), %rdi  ; protocol descriptor for Swift._DefaultCustomPlaygroundQuickLookable + 136 
    0x113a5e447 <+39>: movl $0x28, %esi 
    0x113a5e44c <+44>: movl $0x7, %edx 
    0x113a5e451 <+49>: callq 0x113a826b0    ; swift_rt_swift_allocObject 
    0x113a5e456 <+54>: movq %rbx, 0x10(%rax) 
    0x113a5e45a <+58>: movq %r15, 0x18(%rax) 
    0x113a5e45e <+62>: movb %r14b, 0x20(%rax) 
    0x113a5e462 <+66>: movl 0x10(%rbp), %ecx 
    0x113a5e465 <+69>: movl %ecx, 0x24(%rax) 
    0x113a5e468 <+72>: leaq 0xd4c81(%rip), %rcx  ; partial apply forwarder for closure #2 (Swift.UnsafeBufferPointer<Swift.UInt8>) ->() in Swift._fatalErrorMessage(Swift.StaticString, Swift.StaticString, file: Swift.StaticString, line: Swift.UInt, flags: Swift.UInt32) -> Swift.Never 
    0x113a5e46f <+79>: movq %r12, %rdi 
    0x113a5e472 <+82>: movq %r13, %rsi 
    0x113a5e475 <+85>: movl -0x2c(%rbp), %edx 
    0x113a5e478 <+88>: movq %rax, %r8 
    0x113a5e47b <+91>: callq 0x1138aa1b0    ; function signature specialization <preserving fragile attribute, Arg[1] = [Closure Propagated : reabstraction thunk helper from @callee_owned (@unowned Swift.UnsafeBufferPointer<Swift.UInt8>) ->() to @callee_owned (@unowned Swift.UnsafeBufferPointer<Swift.UInt8>) -> (@out()), Argument Types : [@callee_owned (@unowned Swift.UnsafeBufferPointer<Swift.UInt8>) ->()]> of generic specialization <preserving fragile attribute,()> of Swift.StaticString.withUTF8Buffer<A>((Swift.UnsafeBufferPointer<Swift.UInt8>) -> A) -> A 
-> 0x113a5e480 <+96>: ud2  
    0x113a5e482 <+98>: nopw %cs:(%rax,%rax) 

這裏是你們在詢問該URL的控制檯輸出 - 它看起來像一個類別被點擊時，它的第一類加載的圖像確定，但隨後發現零。

Optional("http://www.afr.com/content/dam/images/h/0/6/g/p/6/image.related.socialLead.620x349.h06bfz.png/1513570709452.jpg") 
Optional("http://www.afr.com/content/dam/images/h/0/6/b/z/i/image.related.afrArticleLead.620x365.h06aej.png/1513559758977.jpg") 
Optional("http://www.afr.com/content/dam/images/h/0/6/f/x/o/image.related.afrArticleLead.620x365.h06bh0.png/1513563680637.jpg") 
Optional("http://assets1.ignimgs.com/2017/12/15/15234538txuhe2cy-1513377967388_1280w.jpg") 
Optional("http://assets1.ignimgs.com/2017/12/18/the-last-jedi-2-1513558653477_1280w.jpg") 
Fatal error: Unexpectedly found nil while unwrapping an Optional value 
2017-12-18 07:07:03.222266+0100 Keyboard[87661:4872775] Fatal error: Unexpectedly found nil while unwrapping an Optional value 
(lldb) 

我該如何優雅地接受函數中的這個nil值？

Answer 1

嘗試下面的代碼，並總是試圖避免強制解包（！）。

extension UIImageView { 

@objc func downloadImage(from url: String){ 

    if let urlconvert = url.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed),let urlConvertible = URL(string:urlconvert){ 

     let urlRequest = URLRequest(url: urlConvertible) 
     let task = URLSession.shared.dataTask(with: urlRequest) { (data, response, error) in 

      if error != nil { 
       print(error as Any) 
       return 
      } 
      DispatchQueue.main.async { 
       if let data = data { 

        self.image = UIImage(data: data) 
       } 
      } 

     } 
     task.resume() 

    } 
    } 

} 

變化這一個

cell.imgView.downloadImage(from: (self.articles?[indexPath.item].imageURL!)!) 

到：

if let imageURL = self.articles?[indexPath.item].imageURL{ 

cell.imgView.downloadImage(from: imageURL) 
}