为什么这个f#代码中的成员字典总是空的？

Question

我想抓取所有网址的页面并将它们放入字典中.我用字典创建了一个类.但我似乎无法在其中添加元素.

type crawler =

     new()= {}
     member this.urls  = new Dictionary<string,string>()
     member this.start (url : string)=
        let hw = new HtmlWeb()
        let doc = hw.Load(url)
        let docNode = doc.DocumentNode
        let links = docNode.SelectNodes(".//a")

        for aLink in links do
            let href = aLink.GetAttributeValue("href"," ")
            if href.StartsWith("http://")  && href.EndsWith(".html") then
              this.urls.Add(href, href)

为什么字典网址是空的？

Answer 1

因为这里的url是在每次调用时都返回新字典的属性.

type Crawler() =  
    let urls = new Dictionary<string,string>()
    member this.Urls  = urls
    member this.Start (url : string)=        
        let hw = new HtmlWeb()        
        let doc = hw.Load(url)        
        let docNode = doc.DocumentNode        
        let links = docNode.SelectNodes(".//a")        
        for aLink in links do            
            let href = aLink.GetAttributeValue("href"," ")            
            if href.StartsWith("http://")  && href.EndsWith(".html") then              
                urls.Add(href, href)