Add A Callback To A Prebuilt Asynchronous Function Swift iOS -

i'm messing around pdfs @ moment. i'm attempting load pdf system , write out same pdf gain understandings of the whole procedure.

the problem i've got i'm having load pdf web , because webviewui.loadrequest asynchronous, isn't completed in time.

    override func viewdidload() {         super.viewdidload()          let filepath = getdocumentsdirectory().stringbyappendingpathcomponent("output.pdf")          let url : nsurl! = nsurl(string: "http://www.nhs.uk/nhsengland/healthcosts/documents/2014/hc5(t)%20june%202014.pdf")          loadtemplate(url, completion: {(webview: uiwebview) -> void in             print("callback started")             let pdf = self.topdf(webview)              {                 pdf!.writetofile(filepath, atomically: true)             } catch {                 // failed write file – bad permissions, bad filename, missing permissions, or more can't converted encoding             }              print("callback started")          })          print("finished viewdidload")      }      func loadtemplate(url: nsurl, completion: (webview: uiwebview) -> void) {         print("start loadtemplate")         // crunching create sketchanimation instance...         let webview = uiwebview(frame: cgrectmake(20, 100, 300, 40))         webview.loadrequest(nsurlrequest(url: url))          self.view.addsubview(webview)          // invoke completion callback         completion(webview: webview)          print("finished loadtemplate")     } 

how add callback loadrequest instead of loadtemplate?

you don't, exactly. you'd set view controller web view's delegate , implement webviewdidfinishload method. in method you'd check make sure load finished 1 after, , if so, you'd invoked code want run when load complete.

here basic example of how set up:

// //  viewcontroller.swift //  import uikit  class viewcontroller: uiviewcontroller, uiwebviewdelegate {      @iboutlet var webview: uiwebview!      var url = nsurl(string: "http://google.com")      override func viewdidload() {         super.viewdidload()          //load initial url         let req = nsurlrequest(url : url!)         webview.delegate = self         webview.loadrequest(req)     }      func webviewdidstartload(webview : uiwebview) {         print("aa")     }      func webviewdidfinishload(webview : uiwebview) {         print("bb")     }  }