ios - WKWebView在后台，几个奇怪的断言

Question

我想在 iOS 中找出当前浏览器的 userAgent。
所以在 Xcode 创建的默认项目中，我添加了:

#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

它打印出我的期望:

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

但之后它会打印:

test4[1930:101220] usage: <WKWebView: 0x7f958f817800; frame = (0 0; 00); layer = <CALayer: 0x60000236ed00>>

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

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

这看起来不太好。我的代码有问题吗，
是否可以避免这些断言并仍然获得 userAgent 字符串？

Answer 1

创建一个空的UIView并添加 WKWebView作为 subview 。