NSInvalidArgumentException'，原因：从 UIWebView 迁移到 WKWebView 时，'Configuration cannot be nil'

Question

I can't seem to find out what is nil. The controller calling this WKWebView is not nil. There must be some type of configuration that I'm not setting. Any Ideas?

HelpViewViewController.h

#import <UIKit/UIKit.h>
#import <WebKit/WebKit.h>

@interface HelpViewViewController : UIViewController
< WKUIDelegate, WKNavigationDelegate>{}



@property (nonatomic, strong) IBOutlet WKWebView *webView;
@property (weak, nonatomic) IBOutlet UIBarButtonItem *sidebarButton;

@property (assign) NSString *urlString;

@end

HelpViewViewController.m

#import "HelpViewViewController.h"
#import "SWRevealViewController.h"
#import "Functions.h"

@interface HelpViewViewController ()

@end

@implementation HelpViewViewController

@synthesize webView,urlString;

NSURL *urlToSave2 = nil;


- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@" start %@",urlString);

This NSLog never gets called. It is crashing before viewDidLoad is called.

    WKWebViewConfiguration *theConfiguration = [[WKWebViewConfiguration alloc] init];
    WKWebView *webView = [[WKWebView alloc] initWithFrame:self.view.frame configuration:theConfiguration];
    webView.navigationDelegate = self;
    NSURL *nsurl=[NSURL URLWithString:@"http://www.apple.com"];
    NSURLRequest *nsrequest=[NSURLRequest requestWithURL:nsurl];
    [webView loadRequest:nsrequest];
    [self.view addSubview:webView];

    
    NSLog(@" end %@",urlString);
}

Answer 1

I couldn't reproduce the error on simulator by adding a WKWebView IBOutlet.

BUT , I did reproduce it if I put a UIWebView object, and change its class in Storyboard to WKWebView .
If that's what you've done to "update your code", please don't do that.
Instead, remove the outlet in Storyboard, and add a new one which is a WKWebView . WKWebView & UIWebView are two different classes even if their "goal" is the same. But they are different, and need different initialization/parameters, and when reading it from Storyboard, when the loading occurs, it breaks everything in that case:

If you open the Storyboard (as source code, ie XML) of a newly added WKWebView outlet, you'll have:

<wkWebView contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="R9K-yX-E6A">
    <rect key="frame" x="0.0" y="0.0" width="320" height="284"/>
    <color key="backgroundColor" red="0.36078431370000003" green="0.38823529410000002" blue="0.4039215686" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
    <wkWebViewConfiguration key="configuration">
        <audiovisualMediaTypes key="mediaTypesRequiringUserActionForPlayback" none="YES"/>
        <wkPreferences key="preferences"/>
    </wkWebViewConfiguration>
</wkWebView>

If you change the class manually of a UIWebView into a WKWebView , you'll have:

<webView contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="JoT-Lq-Nq2" customClass="WKWebView">
    <rect key="frame" x="40" y="341" width="240" height="128"/>
    <color key="backgroundColor" red="0.36078431370000003" green="0.38823529410000002" blue="0.4039215686" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
</webView>

You see that the real class if webView (ie UIWebView ), set to custom WKWebView . BUT , and there is a BUT, if you check carefully the proper one (previous one), you'll see it as a wkWebViewConfiguration tag. It's set in the Storyboard. It's implicitly added when adding the outlet.

Answer 2

Although Apple documentation says that you can create a WKWebView as an outlet, I have not seen an example of that working. I suggest removing it from your xib/storyboard, making it a regular instance variable, and using your in-code initialization.

(In my case, this also required the addition of constraints when it was added as a subview.)