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From "Shazron Abdullah (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CB-12815) WKWebView plugin will not execute Javascript while app is backgrounded
Date Mon, 22 May 2017 23:58:04 GMT

    [ https://issues.apache.org/jira/browse/CB-12815?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16020429#comment-16020429
] 

Shazron Abdullah commented on CB-12815:
---------------------------------------

Thanks Rich,
Since we are supporting iOS 9 and up only (and Promises work since iOS 8), we can possibly
use the replacement you have shown above.
(of course process is a node.js only thing, and won't run in the browser)

> WKWebView plugin will not execute Javascript while app is backgrounded
> ----------------------------------------------------------------------
>
>                 Key: CB-12815
>                 URL: https://issues.apache.org/jira/browse/CB-12815
>             Project: Apache Cordova
>          Issue Type: Bug
>          Components: cordova-plugin-wkwebview-engine
>         Environment: iOS
>            Reporter: Rich Storm
>            Assignee: Shazron Abdullah
>              Labels: Background, Javascript, WKWebView
>
> iOS 10 now has power saving requirements and will not allow background tasks to function
to save battery. For example, a VoIP app can no longer use a polling strategy to stay awake.
The new recommended way, according to Apple (https://developer.apple.com/library/content/documentation/Performance/Conceptual/EnergyGuide-iOS/OptimizeVoIP.html),
is to use VoIP silent push notifications to wake up the app and do the work. 
> I have verified that all VoIP silent push notifications arrive correctly when using the
UIWebView with a vanilla Cordova install. However, when adding the cordova-plugin-wkwebview-engine,
the Javascript callbacks do not fire correctly when receiving the VoIP silent push notification
while the app is in the background. What happens is the first notification is queued, then
the next notification forces the first notification result to the callback. Effectively, making
each push notification 1 behind. When the app is put back into the foreground, the last push
notification callback is fired.
> When the app is in the foreground, all works fine.
> The issue is with the call to "setTimeout" in the iOSExec.nativeCallback function. It
makes sense that if Apple is trying to minimize background execution to save battery, then
they would limit the use of the setTimeout feature. 
> This issue is fixed by changing the iOSExec.nativeCallback function to call the cordova.callbackFromNative
function directly without a setTimeout wrapper. I understand that removing setTimeout is not
an elegant solution and may cause deadlocks. Maybe a new argument isBackground or something
to that effect.
> src/www/ios/ios-wkwebview-exec.js
> {code:javascript}
>     iOSExec.nativeCallback = function(callbackId, status, message, keepCallback, debug)
{
>         var success = status === 0 || status === 1;
>         var args = convertMessageToArgsNativeToJs(message);
>     
>      // setTimeout(function(){
>     	    cordova.callbackFromNative(callbackId, success, status, args, keepCallback);
>      // }, 0);
>     };
> {code}



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