在 iOS 11 使用 webview 发现顶部会有一个空白条，怎么也去不掉，通过设置 contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever 就可以解决了，具体的代码如下：

//
//  ViewController.m
//  webView
//
//  Created by exchen on 18/7/14.
//  Copyright © 2018年 exchen. All rights reserved.
//
 
#import "ViewController.h"
 
@interface ViewController () 
 
@property(nonatomic, strong) UIWebView* webView;
@end
 
@implementation ViewController
 
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    CGRect screen = [[UIScreen mainScreen] bounds];
    
    //添加 UIWebView
    self.webView = [[UIWebView alloc] initWithFrame: CGRectMake(0, 0, screen.size.width, screen.size.height)];
    
    [self.view addSubview: self.webView];
    
    NSURL * url = [NSURL URLWithString: @"https://www.exchen.net"];
    NSURLRequest * request = [NSURLRequest requestWithURL:url];
    [self.webView loadRequest:request];
    self.webView.delegate = self;
    
    //解决 iOS 11 屏幕顶部显示不全
    if ([[UIDevice currentDevice].systemVersion floatValue] >= 11.0) {
        
        self.webView.scrollView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
    }
    
}
 
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
 
- (void)webViewDidStartLoad:(UIWebView *)webView {
    NSLog(@"%@",NSStringFromSelector(_cmd));
}
 
//加载失败时调用
- (void)webView:(UIWebView *)webView didFailLoadWithError:(NSError *)error {
    NSLog(@"%@",NSStringFromSelector(_cmd));
    NSLog(@"error: %@",error);
    
    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"信息" message:@"连接服务器失败，请检查网络" preferredStyle:UIAlertControllerStyleAlert];
    
    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action){
        
        exit(0);
    }];
    
    [alertController addAction:cancelAction];
    
    [self presentViewController:alertController animated:YES completion:nil];
}
 
- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType{
    
    return true;
}
 
@end

原文地址：https://www.exchen.net/%E8%A7%A3%E5%86%B3-ios-11-webview-%E9%A1%B6%E9%83%A8%E7%A9%BA%E7%99%BD%E6%9D%A1%E7%9A%84%E9%97%AE%E9%A2%98.html