WKWebView in background, several strange assertion

Question

I want to find out userAgent of current browser in iOS.

So in default project created by Xcode I added:

#import "ViewController.h"
#import <WebKit/WKWebView.h>

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    dispatch_async(dispatch_get_main_queue(), ^{
        WKWebView *obj = [[WKWebView alloc] initWithFrame:CGRectZero];
        [obj evaluateJavaScript: @"navigator.userAgent" completionHandler:^(id _Nullable result, NSError * _Nullable error) {
            NSLog(@"evaluateJavaScript = %@ : %@", result, error);
            NSLog(@"To make sure that webview alive: %@", obj);
        }];
    });
}


@end

it prints what I expect:

evaluateJavaScript = Mozilla/5.0 (iPad; CPU OS 14_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Mobile/15E148 : (null)

but after that it prints:

test4[1930:101220] usage: <WKWebView: 0x7f958f817800; frame = (0 0; 0 0); layer = <CALayer: 0x60000236ed00>>

test4[1930:101220] [assertion] Error acquiring assertion: <Error Domain=RBSAssertionErrorDomain Code=3 "Target is not running or required target entitlement is missing" UserInfo={RBSAssertionAttribute=<RBSDomainAttribute| domain:"com.apple.webkit" name:"Background" sourceEnvironment:"(null)">, NSLocalizedFailureReason=Target is not running or required target entitlement is missing}>

test4[1930:101220] [ProcessSuspension] 0x102dfed00 - ProcessAssertion: Failed to acquire RBS Background assertion 'WebProcess Background Assertion' for process with PID 1933, error: Error Domain=RBSAssertionErrorDomain Code=3 "Target is not running or required target entitlement is missing" UserInfo={RBSAssertionAttribute=<RBSDomainAttribute| domain:"com.apple.webkit" name:"Background" sourceEnvironment:"(null)">, NSLocalizedFailureReason=Target is not running or required target entitlement is missing}

This doesn't look good. Is something wrong with my code, is it possible to avoid these assertions and still get userAgent string?

just read the error msg "Target is not running or required target entitlement is missing" which is also correct failure because you can apply a different userAgent string with your own implementation you just did. And you assert javascript before the view did load complete. — Ol Sen
@OlSen how did you conclude all that simply by looking at "Target is not running or required target entitlement is missing"? For me this isn't clear at all. — André Herculano
Hm how did you exactly solve this problem? I have a similar issue: stackoverflow.com/questions/67571345/… — Marcel Schürmann
@MarcelSchürmann Reference to webView should keep alive until completionHandler and destroyed in that handler, so in completionHandler I call dispatch_async and then in main queue I destroy webView. — user1244932

Alexey Shikov Alexey Shikov · Accepted Answer · 2020-12-03T16:48:00

-7

votes

Create an empty UIView and add WKWebView as a subview.

WKWebView in background, several strange assertion

1 Answers