在命令行中使用WebView：解開時發現無錯誤

Question

我有一個Cocoa應用程序，它使用WebView加載一些頁面並截取屏幕截圖。

Cocoa程序代碼：

class ViewController: NSViewController, WebFrameLoadDelegate { 

    @IBOutlet var web: WebView! 

    override func viewDidLoad() { 
     super.viewDidLoad() 
     web.frame = NSRect(x: 0, y: 0, width: 1024, height: 768) 
     web.preferences.isJavaScriptEnabled = true 
     web.preferences.isJavaEnabled = true 
     web.preferences.arePlugInsEnabled = true 
     web.frameLoadDelegate = self 
     web.mainFrame.load(URLRequest(url: URL(string: "https://google.com")!)) 
     // Do any additional setup after loading the view. 
    } 

    override var representedObject: Any? { 
     didSet { 
     // Update the view, if already loaded. 
     } 
    } 
    func webView(_ sender: WebView!, didFinishLoadFor frame: WebFrame!) { 

     let queue = DispatchQueue(label: "pic") 
     let delay: DispatchTimeInterval = .seconds(2) 
     queue.asyncAfter(deadline: .now() + delay, execute: { 
      let data = self.web.layer?.data() // data() is a extension on CALayer 
      let nd = NSData(data: data!) 
      nd.write(toFile: "/Users/mac/Desktop/screenshot.png", atomically: true) 
     }) 
    } 
} 

它正常工作，我得到的網頁截圖。

現在，我想到了在命令行而不是Cocoa應用程序。

命令行代碼：

class Main1: NSObject, WebFrameLoadDelegate 
{ 
    var web: WebView! 
    override init() 
    { 
     super.init() 
     web = WebView(frame: CGRect(x: 0, y: 0, width: 1024, height: 768)) 
     web.preferences.isJavaScriptEnabled = true 
     web.preferences.isJavaEnabled = true 
     web.preferences.arePlugInsEnabled = true 
     web.frameLoadDelegate = self 
     web.shouldUpdateWhileOffscreen = true 
     web.mainFrame.load(URLRequest(url: URL(string: "https://google.com")!)) 
    } 

    func webView(_ sender: WebView!, didFinishLoadFor frame: WebFrame!) 
    { 

     let queue = DispatchQueue(label: "pic") 
     let delay: DispatchTimeInterval = .seconds(2) 
     queue.asyncAfter(deadline: .now() + delay, execute: { 
      let data = self.web.layer?.data() 
      let nd = NSData(data: data!) // <-- The data is nil error 
      nd.write(toFile: "/Users/mac/Desktop/screenshot.png", atomically: true) 
     }) 
    } 
} 

extension CALayer { 

/// Get `Data` representation of the layer. 
/// 
/// - Parameters: 
/// - fileType: The format of file. Defaults to PNG. 
/// - properties: A dictionary that contains key-value pairs specifying image properties. 
/// 
/// - Returns: `Data` for image. 

func data(using fileType: NSBitmapImageFileType = .PNG, properties: [String : Any] = [:]) -> Data { 
    let width = Int(bounds.width * self.contentsScale) 
    let height = Int(bounds.height * self.contentsScale) 
    let imageRepresentation = NSBitmapImageRep(bitmapDataPlanes: nil, pixelsWide: width, pixelsHigh: height, bitsPerSample: 8, samplesPerPixel: 4, hasAlpha: true, isPlanar: false, colorSpaceName: NSDeviceRGBColorSpace, bytesPerRow: 0, bitsPerPixel: 0)! 
    imageRepresentation.size = bounds.size 

    let context = NSGraphicsContext(bitmapImageRep: imageRepresentation)! 

    render(in: context.cgContext) 

    return imageRepresentation.representation(using: fileType, properties: properties)! 
} 

} 

let m = Main1() 
RunLoop.main.run() 

我越來越fatal error: unexpectedly found nil while unwrapping an Optional value。

爲什麼我不能在命令行中使用相同的代碼？可能是什麼原因？

如何解決？

謝謝！

P.S. CALayer的擴展名取自here

Answer 1

我在我的機器上試過了你的命令行代碼。

你明白了。

只需添加web.wantsLayer = true，你會得到的截圖，而不是錯誤:-)

提示：它創造了比phantomJS非常大的圖像。如果可能的話，儘量減小圖像大小。