WKWebView 入坑指南

因專案JS互動需要，同時因為支援的系統開始從iOS 8 之後，所以就打算使用WKWebView替換掉專案中的UIWebView。本篇文章會持續更新在使用過程總碰到的問題。

1. 坑一：在使用測試環境時，因為有時後臺返回url並不規範，url不包含scheme時如果呼叫[self.webView loadRequest:request],app就會直接閃退，直接提示exc bad access，沒有任何錯誤的堆疊顯示。而在UIWebView中如果未指定scheme則是自動在url前新增file://。在訪問失敗後呼叫webView:(UIWebView *)webView didFailLoadWithError:(NSError *)error

   代理回撥中返回error。
   如：訪問url如果為www.baidu.com時，WKWebView會直接閃退。而UIWebView則呼叫訪問失敗的代理。url如果為https://www.baidu.com。兩者則都正常。

2. 坑二：在控制器直接呼叫 [self.webView.configuration.userContentController addScriptMessageHandler:self name:@"xxx"] 進行JS互動時，造成迴圈引用無法釋放控制器（self）.打破迴圈引用的方法有兩種:

   中間代理:建立一箇中間代理物件轉發

   @interface WeakScriptMessageDelegate
    
    : NSObject<WKScriptMessageHandler>
   
   @property (nonatomic, weak) id<WKScriptMessageHandler> scriptDelegate;
   
   - (instancetype)initWithDelegate:(id<WKScriptMessageHandler>)scriptDelegate;
   
   @end
   
   @implementation WeakScriptMessageDelegate
   
   - (instancetype)initWithDelegate:(id<WKScriptMessageHandler>)scriptDelegate {
       self
    
    = [super init];
        if (self) {
        _scriptDelegate = scriptDelegate;
       }
        return self;
   }
   
   - (void)userContentController:(WKUserContentController *)userContentController didReceiveScriptMessage:(WKScriptMessage *)message {
       [self.scriptDelegate userContentController:userContentController didReceiveScriptMessage:message];
   }
   @end

   使用時:
   WKUserContentController *userContentController = [[WKUserContentController alloc] init];
   [userContentController addScriptMessageHandler:[[WeakScriptMessageDelegate alloc] initWithDelegate:self] name:@"xxx"];
   

   手動釋放,在檢視控制器Appear時新增，Disappear時移除。

   
   - (void)viewWillAppear:(BOOL)animated {
   [super viewWillAppear:animated];
   WKUserContentController *controller = self.webView.configuration.userContentController;
   [self.webView.configuration.userContentController addScriptMessageHandler:self name:@"xxx"];
   
   }
   - (void)viewWillDisappear:(BOOL)animated {
       [super viewWillDisappear:animated];
       WKUserContentController *controller = self.webView.configuration.userContentController;
       [controller  removeScriptMessageHandlerForName:@"xxx"];
   }