在开发过程中，iOS 中实现加载 web 页面主要有两种控件，UIWebView 和 WKWebview，两种控件对应具体的实现方法不同。WKWebView是苹果公司在iOS8系统推出的，这里主要概述WebKit中更新的WKWebView控件的新特性与使用方法，以及小编在开发过程中踩的坑。

一、相比于UIWebView的优势：

1. 在性能、稳定性、占用内存方面有很大提升；
2. 允许JavaScript的Nitro库加载并使用（UIWebView中限制）
3. 增加加载进度属性：estimatedProgress，不用在自己写假进度条了
4. 支持了更多的HTML的属性

二、WKWebview的常用属性

@property (nullable, nonatomic, readonly, copy) NSString *title;

@property (nullable, nonatomic, readonly, copy) NSURL *URL;

@property (nonatomic, readonly, getter=isLoading) BOOL loading;
//加载进度
@property (nonatomic, readonly) double estimatedProgress;

三、WKWebview的常用方法

- (nullable WKNavigation *)loadRequest:(NSURLRequest *)request;

• (nullable WKNavigation *)loadFileURL:(NSURL *)URL allowingReadAccessToURL:(NSURL *)readAccessURL API_AVAILABLE(macosx(10.11), ios(9.0));

• (nullable WKNavigation *)loadHTMLString:(NSString *)string baseURL:(nullable NSURL *)baseURL;

• (nullable WKNavigation *)loadData:(NSData *)data MIMEType:(NSString *)MIMEType characterEncodingName:(NSString *)characterEncodingName baseURL:(NSURL *)baseURL API_AVAILABLE(macosx(10.11), ios(9.0));

四、WKNavigationDelegate代理的方法

#pragma mark - WKNavigationDelegate
/* 页面开始加载 */

• (void)webView:(WKWebView *)webView didStartProvisionalNavigation:(WKNavigation *)navigation{
  NSLog(@"页面开始加载");
  }
  /* 开始返回内容 */

• (void)webView:(WKWebView *)webView didCommitNavigation:(WKNavigation *)navigation{
  NSLog(@"开始返回内容");
  }
  /* 页面加载完成 */

• (void)webView:(WKWebView *)webView didFinishNavigation:(WKNavigation *)navigation{
  NSLog(@"页面加载完成");
  }
  /* 页面加载失败 */

• (void)webView:(WKWebView *)webView didFailProvisionalNavigation:(WKNavigation *)navigation{
  NSLog(@"页面加载失败");
  }
  /* 在发送请求之前，决定是否跳转 */

• (void)webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler{
  //允许跳转
  decisionHandler(WKNavigationActionPolicyAllow);
  //不允许跳转
  //decisionHandler(WKNavigationActionPolicyCancel);
  }
  /* 在收到响应后，决定是否跳转 */

• (void)webView:(WKWebView *)webView decidePolicyForNavigationResponse:(WKNavigationResponse *)navigationResponse decisionHandler:(void (^)(WKNavigationResponsePolicy))decisionHandler{

  NSLog(@"%@",navigationResponse.response.URL.absoluteString);
  //允许跳转
  decisionHandler(WKNavigationResponsePolicyAllow);
  //不允许跳转
  //decisionHandler(WKNavigationResponsePolicyCancel);
  }

五、小编的实例Demo

首先遵守协议：

其次创建一个WKWebView

#pragma mark - 创建webView

• (void)createWebView{

  WKWebViewConfiguration *config = [[WKWebViewConfiguration alloc] init];
  config.selectionGranularity = WKSelectionGranularityDynamic;
  config.allowsInlineMediaPlayback = YES;
  WKPreferences *preferences = [WKPreferences new];
  //是否支持JavaScript
  preferences.javaScriptEnabled = YES;
  //不通过用户交互，是否可以打开窗口
  preferences.javaScriptCanOpenWindowsAutomatically = YES;
  config.preferences = preferences;
  self.webView = [[WKWebView alloc] initWithFrame:self.view.bounds];
  [self.view addSubview:self.webView];

  /* 加载服务器url的方法*/
  NSString *url = @"https://www.baidu.com";
  NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:url]];
  [self.webView loadRequest:request];

  self.webView.navigationDelegate = self;
  self.webView.UIDelegate = self;

}

这样就可以在webView中正常加载百度首页了。

不过，在开发中有时遇到网络不佳的时候，想给用户显示一个加载网页的进度，加载完成后，想再navigation中显示网页的标题，就需要对WKWebView的"estimatedProgress"和

"title"进行监听了。

首先创建一个进度条

- (void)createProgressView{
self.progressView = [[UIProgressView alloc] initWithFrame:CGRectMake(, , SCREEN_WIDTH, )];
self.progressView.progressViewStyle = UIProgressViewStyleDefault;
self.progressView.tintColor = [UIColor blueColor];
self.progressView.trackTintColor = [UIColor greenColor];
[self.view addSubview:self.progressView];
}

让webView对“进度”和“标题”进行监听

[self.webView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionNew context:nil];
[self.webView addObserver:self forKeyPath:@"title" options:NSKeyValueObservingOptionNew context:NULL];

最后，完成对KVO的回调

#pragma mark - KVO回馈
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
if ([keyPath isEqualToString:@"estimatedProgress"]) {
double progress = _webView.estimatedProgress;
self.progressView.alpha = 1.0f;
[self.progressView setProgress:progress animated:YES];
if(progress >= ){
[UIView animateWithDuration:0.25 delay:0.25 options:UIViewAnimationOptionCurveEaseOut animations:^{
self.progressView.alpha = 0.0f;
} completion:^(BOOL finished) {
[self.progressView setProgress:0.0f animated:NO];
}];
}
if ([change[@"new"] floatValue] <[change[@"old"] floatValue]) {
return;
}
if ([change[@"new"]floatValue] == 1.0) {
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(. * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

        });  
    }  
}  
else if (\[keyPath isEqualToString:@"title"\]){  
    self.title = change\[@"new"\];  
}  

}

这样就实现了对加载进度的显示了。