application crashes trying to communicate between swift code and javascript

Would you mind showing the part of code where the error occurs ? Otherwise, nearly impossible to analyze your problem through your personal interpretation of it.

//This is the Swift Code which returns data to javascript

// Call this function when you have results to send back to javascript callbacks

// callbackId : int comes from handleCall function

// args: list of objects to send to the javascript callback

func returnResult(callbackId:Int,args:Any...) {

if callbackId==0 {

return

}

var resultArray=[Any]()

if !args.isEmpty {

for arg in args {

var argJSONString:String = ""

if JSONSerialization.isValidJSONObject(arg) {

let data = try! JSONSerialization.data(withJSONObject: arg, options: .prettyPrinted)

argJSONString=String(data:data,encoding:.utf8)!

}

resultArray.append(argJSONString)

}

}

if JSONSerialization.isValidJSONObject(resultArray) {

let data = try! JSONSerialization.data(withJSONObject: resultArray, options: .prettyPrinted)

let resultArrayString:String=String(data:data, encoding:.utf8)!

// We need to perform selector with afterDelay 0 in order to avoid weird recursion stop

// when calling NativeBridge in a recursion more then 200 times :s (fails onto 201th calls!!!)

let javascriptFuncStringLocal:String="NativeBridge.resultForCallback(\(callbackId),\(resultArrayString));"

self.perform(#selector(self.returnResultAfterDelay(javascriptFuncString:)), with: javascriptFuncStringLocal, afterDelay: 1)

}

}

@objc func returnResultAfterDelay(javascriptFuncString:String) {

self.webView.performSelector(onMainThread: #selector(self.webView.evaluateJavaScript(_:completionHandler:)), with: javascriptFuncString, waitUntilDone: false)

}

//Javascript code where response from native is handled

// Automatically called by native layer when a result is available

resultForCallback : function resultForCallback(callbackId, resultArray) {

console.log("In result for call back")

try {

var callback = NativeBridge.callbacks[callbackId];

if (!callback) return;

callback.apply(null,resultArray);

} catch(e) {alert(e)}

}

It retuns data to javascript but abruptly crashes after 2/3 call backs. It doesn't stop on any perticular line of code. It just through an exception in AppDelegate

class AppDelegate: UIResponder, UIApplicationDelegate {

Where does

NativeBridge

WKWebView

WKScriptMessage

NativeBridge

btw Your ‘perform selector after delay’ stuff is super scary because it drags you outside of Swift’s type checked environment. I recommend that you use

DispatchQueue.main.asyncAfter(…)

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

Thanks a lot. It worked. 😀

DispatchQueue.main.asyncAfter(…) solved my problem. It stopped crashing.

And yes, NativeBridge is a javascript wrapper (message come in and out point for javascript side) which communicate with swift code by posting message using WKScriptMessageHandler only.