iOS CDVWKInAppBrowser evaluateJavascript method randomly gets blocked on iOS 12

[jonathanli2]

Hi,
While testing the new ios inappbrowser plugin with wkwebview on iOS 12 device, when the javascript code calls injectScriptCode method, the application may hang.
The reason is in CDVWKInAppBrowser.m, the completing block of evaluateJavascrip method is not called, so the method stuck in the while (!finished) loop

_- (NSString *)evaluateJavaScript:(NSString *)script {
__block NSString resultString = nil;
__block BOOL finished = NO;
__block NSString _script = script;
NSLog(@"evaluateJavaScript: %@", script);
[self.inAppBrowserViewController.webView evaluateJavaScript:script completionHandler:^(id result, NSError *error) {
NSLog(@"evaluatejavascript result: %@, %@", result, error);
if (error == nil) {
if (result != nil) {
resultString = result;
NSLog(@"%@", resultString);
}
} else {
NSLog(@"evaluateJavaScript error : %@ : %@", error.localizedDescription, _script);
}
finished = YES;
}];

while (!finished)
{
    NSLog(@"CDVWKInAppbrowser evaluateJavaScript runloop");
    [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
}
NSLog(@"evaluateJavaScript: %@", resultString);
return resultString;

}_

The xcode console log has the below output. After calling evaluatejavascript method, it calls runloop method few times in while block, and then just stops, the app is idle.

2018-11-02 09:44:32.646767-0400 wk[5669:2032638] evaluateJavaScript: (function(w){if(!w._cdvMessageHandler) {w._cdvMessageHandler = function(id,d){w.webkit.messageHandlers.cordova_iab.postMessage({d:d, id:id});}}})(window)
2018-11-02 09:44:39.013119-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.013583-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.013827-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.014057-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.014336-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.014561-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.014789-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.015012-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.015234-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.015455-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.015676-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.015898-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.016120-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.016400-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.016622-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.016848-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.017239-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.021299-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.037837-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:44:39.054533-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop
2018-11-02 09:45:47.383791-0400 wk[5669:2032638] CDVWKInAppbrowser evaluateJavaScript runloop

I saw someone else also reported the same issue on ios 12 device testing at
https://stackoverflow.com/questions/26778955/wkwebview-evaluate-javascript-return-value
(see the first answer), so this may relate to the iOS 12 behavior change.

Thanks for help.

Jonathan

[jonathanli2]

Add the comment from
https://stackoverflow.com/questions/26778955/wkwebview-evaluate-javascript-return-value

"This solution IS NOT WORKING anymore. The callback now called from the main Thread and if you lock the main thread in the while loop (like in this solution), the callback handler will be never called. evaluateJavaScript waits for main thread released, but it never happens because it locked in the loop. – Mike Keskinov Sep 4 at 0:21"

[jonathanli2]

As the return value from CDVWKInAppbrowser's evaluateJavascript method is actually never used, it may well just changes the function signature to
- (void)evaluateJavaScript:(NSString *)script
and so we can remove the while loop which blocks the method from returning.

Thanks
Jonathan

[jonathanli2]

A change has been made at the pull request
#341

[janpio]

Could you take a look please @dpa99c?

[dpa99c]

The PR changes look good to me:
as @jonathanli2 points out, the synchronous return value is never used in CDVWKInAppbrowser since the result is returned asynchronously via the postMessage API.
The loop was just a hangover from the UIWebView implementation that I forgot to take out.

[jonathanli2]

Any update for this pull request?

[jonathanli2]

The pull request has been merged, and the issue is closed.

Thanks
Jonathan

[janpio]

(FYI: If you use closes #340 in the text of a PR, it will automatically close the issue when the PR is merged. Can use that for your next PR.)