由於NSAttributedString UITableView滾動不平滑

Question

我使用NSAttributedString將html字符串轉換爲attributedString。我已經轉換它，但label在單元格，所以我寫下面的代碼cellForRowAtIndex，當我應用此代碼tableview不滾動平滑。如果我用簡單的文字刪除它，它會順利滾動。

cell.lblDescription.setHTMLFromString(htmlText: model.strItineraryDescription) 

我必須轉換到html stringattributed string

extension UILabel { 

    func setHTMLFromString(htmlText: String) { 
     let modifiedFont = NSString(format:"<span style=\"font-family: '-apple-system', 'HelveticaNeue'; font-size: \(self.font!.pointSize)\">%@</span>" as NSString, htmlText) as String 


     //process collection values 
     let attrStr = try! NSAttributedString(
      data: modifiedFont.data(using: .unicode, allowLossyConversion: true)!, 
      options: [NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType, NSCharacterEncodingDocumentAttribute: String.Encoding.utf8.rawValue], 
      documentAttributes: nil) 


     self.attributedText = attrStr 
    } 

} 

我html string是

<strong><u>Featured Program</u></strong></p> 
\n<ol> 
\n <li>Arrival at Delhi airport. You will receive by our representative.</li> 
\n <li>Driving to Agra and exploring the city.</li> 
\n <li>Back to Hotel for Overnight stay.</li> 
\n</ol> 
\n<p><strong>City Features</strong></p> 
\n<ol> 
\n <li><strong>Visit to Agra Fort \U2013 </strong>Former Name Badalgarh, Shah-Jahan spent his last eight years here. You can watch the mesmerizing view of Taj Mahal from this fort just like Shah Jahan.</li> 
\n <li><strong>Visit to Taj Mahal \U2013</strong> It took 21 years to build and stood in 1653. The palace is considered as the symbol of love. Shah Jahan built this wonder in the memory of his wife Mumtaj Mahal.</li> 
\n</ol> 
\n<p><strong>(Both Agra Fort and Taj Mahal are UNESCO Declared world heritage site)</strong> 

Answer 1

這說明什麼html2AttributedString呢？它是否將HTML轉換爲cellForRowAtIndexPath上的動態屬性字符串？如果是的話，這實際上是花時間。我們可以通過在模型中緩存HTML的等效屬性字符串來加快內存速度。所以這種重新加載的方式會在單元創建或重用期間獲取準備好的屬性字符串。

例如，僞碼：

class MyModel 
{ 
    var myHTML: String = "" 
    var myHTML2AttributedString: String = "" 
} 


class ModelMapping 
{ 
    ... 
    myModel.myHTML = responseFromJSON["htmlText"] 
    myModel.myHTML2AttributedString = customFuncToConvertHTMLToAttributed(myModel.myHTML) 
    ... 
} 

class ViewController 
{ 
    ... 
    cell.lblDescription.attributedText = myModel.myHTML2AttributedString // This one would be cached Attributed string equivalent of HTML string. 
    ... 
} 

希望幫助！

編輯：從NeverHopeless

class MyModel 
{ 
    var myAttributedHTML: NSMutableAttributedString = "" 
    var strItineraryDescription: String = "" 

    func prepareHTMLFromString() { 
     let modifiedFont = NSString(format:"<span style=\"font-family: '-apple-system', 'HelveticaNeue'; font-size: \(self.font!.pointSize)\">%@</span>" as NSString, self.strItineraryDescription) as String 


     //process collection values 
     let attrStr = try! NSAttributedString(
      data: modifiedFont.data(using: .unicode, allowLossyConversion: true)!, 
      options: [NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType, NSCharacterEncodingDocumentAttribute: String.Encoding.utf8.rawValue], 
      documentAttributes: nil) 


     myAttributedHTML = attrStr.mutableCopy() 
    } 
} 

class MyViewController 
{ 
    ... 
    cell.lblDescription.attributedText = myModel.myAttributedHTML 
    ... 
} 

class ResponseHandler 
{ 
    ... 
    myModel.strItineraryDescription = responseFromServer["myHTML"] 
    myModel.prepareHTMLFromString() 
    ... 
} 

Answer 2

您需要使用調度隊列

DispatchQueue.global(qos: .background).async { 
    print("This is run on the background queue") 
    let strmy = model.strItineraryDescription.html2AttributedString    

    DispatchQueue.main.async { 
     cell.lblDescription.attributedText = strmy 

    } 
}