#import "QLCWebViewController.h"#import 
     
      @interface QLCWebViewController ()@property (weak, nonatomic) IBOutlet UIView *contentView;@property (weak, nonatomic) IBOutlet WKWebView *webView;@property (weak, nonatomic) IBOutlet UIBarButtonItem *backItem;@property (weak, nonatomic) IBOutlet UIBarButtonItem *forwardItem;@property (weak, nonatomic) IBOutlet UIProgressView *progressView;@end@implementation QLCWebViewController- (IBAction)goBack:(id)sender {    [self.webView goBack];}- (IBAction)goForward:(id)sender {    [self.webView goForward];}- (IBAction)reload:(id)sender {    [self.webView reload];}#pragma mark - 生命周期方法- (void)viewDidLayoutSubviews{    [super viewDidLayoutSubviews];        _webView.frame = self.contentView.bounds;}- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view from its nib.    // 添加webView    WKWebView *webView = [[WKWebView alloc] init];    _webView = webView;    [self.contentView addSubview:webView];        // 展示网页    NSURLRequest *request = [NSURLRequest requestWithURL:_url];    [webView loadRequest:request];        // KVO监听属性改变    /*        Observer:观察者        KeyPath:观察webView哪个属性        options:NSKeyValueObservingOptionNew:观察新值改变             KVO注意点.一定要记得移除     */    [webView addObserver:self forKeyPath:@"canGoBack" options:NSKeyValueObservingOptionNew context:nil];    [webView addObserver:self forKeyPath:@"canGoForward" options:NSKeyValueObservingOptionNew context:nil];    [webView addObserver:self forKeyPath:@"title" options:NSKeyValueObservingOptionNew context:nil];        // 进度条    [webView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionNew context:nil];    }// 只要观察对象属性有新值就会调用- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary
      
        *)change context:(void *)context{    self.backItem.enabled = self.webView.canGoBack;    self.forwardItem.enabled = self.webView.canGoForward;    self.title = self.webView.title;    self.progressView.progress = self.webView.estimatedProgress;    self.progressView.hidden = self.webView.estimatedProgress >= 1;}#pragma mark - 对象被销毁- (void)dealloc{    [self.webView removeObserver:self forKeyPath:@"canGoBack"];    [self.webView removeObserver:self forKeyPath:@"title"];    [self.webView removeObserver:self forKeyPath:@"canGoForward"];    [self.webView removeObserver:self forKeyPath:@"estimatedProgress"];}@end