DSBridge-iOS源码解析

DSBridge-iOS源码解析

Objective-C与JavaScript间的交互方式

1. 自定义scheme, 拦截http请求

     在iOS7以前, Objective-C与JavaScript间的交互采用的就是这种方式, JavaScript调用native的API时, 通过约定固定的scheme, 然后用window.location的方式触发UIWebView的shouldStartLoadWithRequest:的代理方法来达到调用native API的目的; native通过UIWebView提供的stringByEvaluatingJavaScriptFromString:方法来调用JavaScript API.

2. 通过JavaScriptCore获取JavaScript运行环境

     在iOS7时, 苹果推出了JavaScriptCore公共框架, 它提供了简单的方式实现在Objective-C与JavaScript间交互. 通过JavaScriptCore进行Objective-C与JavaScript间通讯时, 必须先用获取到UIWebView的JSContext, 即JavaScript的运行环境, 然后将交互对象注入到JSContext中, 这样Objective-C与JavaScript就能通过注入的交互对象进行通讯了.

注入Objective-C与JavaScript的交互对象的时机

1. UIWebView创建JSContext的时机

• 当UIWebView加载页面解析到
  • 2. native方法调用JavaScript函数

  // addValue JavaScript函数
  // arguments 参数
  // completionHandler 回调
  [_webview callHandler:@"addValue"
                      arguments:[[NSArray alloc] initWithObjects:@1,@"hello", nil]
              completionHandler:^(NSString * value){
                  NSLog(@"%@",value);
              }];
              
  -(void)callHandler:(NSString *)methodName arguments:(NSArray *)args completionHandler:(void (^)(NSString *))completionHandler {
      if(!args) {
          args=[[NSArray alloc] init];
      }
      // 在window对象上通过函数名addValue找到h5注册的JavaScript函数, 最终通过webView的stringByEvaluatingJavaScriptFromString:方法调用
      NSString *script=[NSString stringWithFormat:@"(window._dsf.%@||window.%@).apply(window._dsf||window,%@)",methodName,methodName,[JSBUtil objToJsonString:args]];
      [self evaluateJavaScript:script completionHandler:^(NSString * value){
          if(completionHandler) completionHandler(value);
      }];
  }
  
  

  JavaScript调用native API

  原理图

  call_native.png
  • 1.H5发起调用请求

  // 获取交互对象
  var bridge = getJsBridge();
  function callSyn() {
  // 通过bridge的call方法调用native方法testSyn, 传递参数为{msg: "testSyn"}
      bridge.call("testSyn", {msg: "testSyn"});
  }
  
  // b native API 方法名
  // a 调用native API时传递给native方法的参数
  // c JavaScript的回调函数, 当异步调用native API时会传递此参数
  call: function(b, a, c) {
      'function' == typeof a && (c = a, a = {});
      if('function' == typeof c) {
          window.dscb = window.dscb || 0;
          var d = 'dscb' + window.dscb++;
          // 在window下添加对象d, 保存JavaScript回调函数c
          window[d] = c;
          // 将d放置在参数列表a中, 传递给native方法, 最终在native方法里, 通过在参数列表的json字符串中取出d, 
          // 然后在window对象中通过d获取JavaScript的回调函数c来完成回调操作
          a._dscbstub = d;
      }
      a = JSON.stringify(a || {});
      // 通过_dsbridge交互对象调用native API
      return window._dswk? prompt(window._dswk + b, a): 'function' == typeof _dsbridge? _dsbridge(b, a): _dsbridge.call(b, a)
  }
  
  

  • 2.触发交互对象block执行

  ctx[@"_dsbridge"]=^(NSString * method,NSString * args){
          return [JSBUtil call:method :args JavascriptInterfaceObject:JavascriptInterfaceObject jscontext:ctx_];
      };
  

  • 3.方法解析并调用

  +(NSString *)call:(NSString*) method :(NSString*) args  JavascriptInterfaceObject:(id) JavascriptInterfaceObject jscontext:(id) jscontext {
  // 方法及参数解析
  // methodOne为同步调用时的方法名称, 此时methodTwo为空
      NSString *methodOne = [JSBUtil methodByNameArg:1 selName:method class:[JavascriptInterfaceObject class]];
  // methodTwo为异步调用时的方法名称, 此时methodOne为空
      NSString *methodTwo = [JSBUtil methodByNameArg:2 selName:method class:[JavascriptInterfaceObject class]];
      SEL sel=NSSelectorFromString(methodOne);
      SEL selasyn=NSSelectorFromString(methodTwo);
      NSString *error=[NSString stringWithFormat:@"Error! \n Method %@ is not invoked, since there is not a implementation for it",method];
      NSString *result=@"";
      // 检查调用对象是否存在
      if(!JavascriptInterfaceObject) {
          NSLog(@"Js bridge method called, but there is not a JavascriptInterfaceObject, please set JavascriptInterfaceObject first!");
      } else {
      // json为发起调用时的参数列表
          NSDictionary * json=[JSBUtil jsonStringToObject:args];
      // cb 保存JavaScript的回调函数名称, 当发起异步调用时为有值
          NSString * cb;
          do{
              if(json && (cb= [json valueForKey:@"_dscbstub"])) {
              // 异步调用
                  if([JavascriptInterfaceObject respondsToSelector:selasyn]) {
                      void (^completionHandler)(NSString *,BOOL) = ^(NSString * value,BOOL complete) {
                          value=[value stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding];
                          NSString *del=@"";
                          // 发起连续回调时, complete为YES, 否则为NO
                          if (complete) {
                          // 删除保存在window对象中的cb对象, 这个对象是H5发起调用时保存到window中的
                             del=[@"delete window." stringByAppendingString:cb];
                          }
                          // 在window对象上通过cb调用JavaScript函数
                          NSString*js=[NSString stringWithFormat:@"try {%@(decodeURIComponent(\"%@\"));%@; } catch(e){};",cb,(value == nil) ? @"" : value,del];
                          if([jscontext isKindOfClass:JSContext.class]) {
                              [jscontext evaluateScript:js ];
                          } else if([jscontext isKindOfClass:WKWebView.class]) {
                              @synchronized(jscontext) {
                                  UInt64  t=[[NSDate date] timeIntervalSince1970]*1000;
                                  g_ds_js_cache=[g_ds_js_cache stringByAppendingString:js];
                                  if(t-g_ds_last_call_time<50) {
                                      if(!g_ds_have_pending){
                                          [self evalJavascript:(WKWebView *)jscontext :50];
                                          g_ds_have_pending=true;
                                      }
                                  } else {
                                      [self evalJavascript:(WKWebView *)jscontext  :0];
                                  }
                              }
                          }
                      };
                      SuppressPerformSelectorLeakWarning(
                                                         [JavascriptInterfaceObject performSelector:selasyn withObject:json withObject:completionHandler];
                                                         );
                      //when performSelector is performing a selector that return value type is void,
                      //the return value of performSelector always seem to be the first argument of the selector in real device(simulator is nil).
                      //So,you should declare the return type of all api as NSString explicitly.
                      if (result==(id)json) {
                          result=@"";
                      }
                      break;
                  }
              } else if ([JavascriptInterfaceObject respondsToSelector:sel]) {
              // 同步调用
                  SuppressPerformSelectorLeakWarning(
                                                     result=[JavascriptInterfaceObject performSelector:sel withObject:json];
                                                     );
                  break;
              }
              NSString*js=[error stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding];
              js=[NSString stringWithFormat:@"window.alert(decodeURIComponent(\"%@\"));",js];
              if ([jscontext isKindOfClass:JSContext.class]) {
                  [jscontext evaluateScript:js ];
              } else if ([jscontext isKindOfClass:WKWebView.class]) {
                  [(WKWebView *)jscontext evaluateJavaScript :js completionHandler:nil];
              }
              NSLog(@"%@",error);
          }while (0);
      }
      if (result == nil||![result isKindOfClass:[NSString class]]) {
          result=@"";
      }
      return result;
  }