针对的是UIWebView

如果不使用 UIWebView 此库已经过时了。但是思想值得学习。

思路

1、注入一个全局对象 EasyJS。
__callbacks 负责以 callbackid 为key 存储 回调函数。
invokeCallback 负责根据OC端回传的 callbackid 从 __callbacks 拿出 回调函数 并调用
call 负责拼接 iframe的src 调用起OC端代理方法 在代理方法中解析 类名 方法名 参数 以及回调 callbackid
inject 负责以生成 {obj:{jsMethod:function (){
return EasyJS.call(obj, method, Array.prototype.slice.call(arguments));
},...}} ，并加入到全局window中。

JS端 代码解析

inject: function (obj, methods){
        window[obj] = {};
        var jsObj = window[obj];
        
        for (var i = 0, l = methods.length; i < l; i++){
            (function (){
                var method = methods[i];
                var jsMethod = method.replace(new RegExp(":", "g"), "");
         // 此处将匿名函数 作为键值对保存 类似于block 
        // 应该注意到 arguments 是变化的 在具体的调用时才确定个数和参数类型 类似于OC的可变参数方法
                jsObj[jsMethod] = function (){
                    return EasyJS.call(obj, method, Array.prototype.slice.call(arguments));
                };
            })();
        }
    }

//例如 arguments 只有一个 而且是函数类型
MyJSTest.testWithFuncParam(function (data){
    alert(data); //data would be blabla:"bla
    return "some data";
});
//所以当调用时 
    call: function (obj, functionName, args){
        var formattedArgs = [];

        for (var i = 0, l = args.length; i < l; i++){
            //根据args[i] 类型来判断是否有回调函数
            if (typeof args[i] == "function"){
                formattedArgs.push("f");
                var cbID = "__cb" + (+new Date);
// 类似于 WebViewJavascriptBridge 生成唯一callbackid 和全局字典保存回调函数 并将 callbackid 通过代理传递给OC
                EasyJS.__callbacks[cbID] = args[i];
                formattedArgs.push(cbID);
            }else{
                formattedArgs.push("s");
                formattedArgs.push(encodeURIComponent(args[i]));
            }
        }
        
        var argStr = (formattedArgs.length > 0 ? ":" + encodeURIComponent(formattedArgs.join(":")) : "");
        
        var iframe = document.createElement("IFRAME");
        iframe.setAttribute("src", "easy-js:" + obj + ":" + encodeURIComponent(functionName) + argStr);
        document.documentElement.appendChild(iframe);
        iframe.parentNode.removeChild(iframe);
        iframe = null;
        
// 不理解的是 获取返回值的时候 不用考虑时机 一定能获取到？如果调用的OC方法很耗时 呢？
        var ret = EasyJS.retValue;
        EasyJS.retValue = undefined;
        
        if (ret){
            return decodeURIComponent(ret);
        }
    }
//最后是处理回调
    invokeCallback: function (cbID, removeAfterExecute){
        var args = Array.prototype.slice.call(arguments);
// 这两步是 因为前两个参数是不需要的 丢弃
        args.shift();
        args.shift();
        
        for (var i = 0, l = args.length; i < l; i++){
            args[i] = decodeURIComponent(args[i]);
        }
        //根据回传的callbackid 取出调用call时存储的回调函数 
               // 执行
        var cb = EasyJS.__callbacks[cbID];
        if (removeAfterExecute){
            EasyJS.__callbacks[cbID] = undefined;
        }
        return cb.apply(null, args);
    },

OC端 代码解析

核心方法

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType{
    
    NSString *requestString = [[request URL] absoluteString];
    
    if ([requestString hasPrefix:@"easy-js:"]) {
        /*
         A sample URL structure:
         easy-js:MyJSTest:test
         easy-js:MyJSTest:testWithParam%3A:haha
         */
        NSArray *components = [requestString componentsSeparatedByString:@":"];
        //NSLog(@"req: %@", requestString);
        //利用动态运行时 构建 NSInvocation 执行方法
        NSString* obj = (NSString*)[components objectAtIndex:1];
        NSString* method = [(NSString*)[components objectAtIndex:2]
                            stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
        
        NSObject* interface = [javascriptInterfaces objectForKey:obj];
        
        // execute the interfacing method
        SEL selector = NSSelectorFromString(method);
        NSMethodSignature* sig = [[interface class] instanceMethodSignatureForSelector:selector];
        NSInvocation* invoker = [NSInvocation invocationWithMethodSignature:sig];
        invoker.selector = selector;
        invoker.target = interface;
        
        NSMutableArray* args = [[NSMutableArray alloc] init];
        // 判断是否有参数传递
        if ([components count] > 3){
            NSString *argsAsString = [(NSString*)[components objectAtIndex:3]
                                      stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
            
            NSArray* formattedArgs = [argsAsString componentsSeparatedByString:@":"];
            for (int i = 0, j = 0, l = [formattedArgs count]; i < l; i+=2, j++){
                NSString* type = ((NSString*) [formattedArgs objectAtIndex:i]);
                NSString* argStr = ((NSString*) [formattedArgs objectAtIndex:i + 1]);
                // 是否有回调函数
                if ([@"f" isEqualToString:type]){
// 有回调函数 则构建  EasyJSDataFunction 实例 ，传参给具体的调用函数 此实例会调用 executeWithParams 来实现回调
                    EasyJSDataFunction* func = [[EasyJSDataFunction alloc] initWithWebView:(EasyJSWebView *)webView];
                    func.funcID = argStr;//回调的callbackid
                    [args addObject:func];
                    [invoker setArgument:&func atIndex:(j + 2)];
                }else if ([@"s" isEqualToString:type]){
                    NSString* arg = [argStr stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
                    [args addObject:arg];
                    [invoker setArgument:&arg atIndex:(j + 2)];
                }
            }
        }
        [invoker invoke];
        
        //return the value by using javascript
        if ([sig methodReturnLength] > 0){
// 执行这段代码的时机 和 一定 比js拿取返回值的时机延后吗？？？
            NSString* retValue;
            [invoker getReturnValue:&retValue];
            
            if (retValue == NULL || retValue == nil){
                [webView stringByEvaluatingJavaScriptFromString:@"EasyJS.retValue=null;"];
            }else{
                retValue = (NSString *)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(NULL,(CFStringRef) retValue, NULL, (CFStringRef)@"!*'();:@&=+$,/?%#[]", kCFStringEncodingUTF8));
                [webView stringByEvaluatingJavaScriptFromString:[@"" stringByAppendingFormat:@"EasyJS.retValue=\"%@\";", retValue]];
            }
        }
        
        [args release];
        
        return NO;
    }
    
    if (! self.realDelegate){
        return YES;
    }
    
    return [self.realDelegate webView:webView shouldStartLoadWithRequest:request navigationType:navigationType];
}

//EasyJSDataFunction 类  核心方法 直接调用js 回传callbackid 和参数
- (NSString*) executeWithParams: (NSArray*) params{
    NSMutableString* injection = [[NSMutableString alloc] init];
    
    [injection appendFormat:@"EasyJS.invokeCallback(\"%@\", %@", self.funcID, self.removeAfterExecute ? @"true" : @"false"];
    // 拼接回调的参数 如果有的话
    if (params){
        for (int i = 0, l = params.count; i < l; i++){
            NSString* arg = [params objectAtIndex:i];
            NSString* encodedArg = (NSString*) CFURLCreateStringByAddingPercentEscapes(NULL, (CFStringRef)arg, NULL, (CFStringRef) @"!*'();:@&=+$,/?%#[]", kCFStringEncodingUTF8);
            
            [injection appendFormat:@", \"%@\"", encodedArg];
        }
    }
    
    [injection appendString:@");"];
    
    if (self.webView){
        return [self.webView stringByEvaluatingJavaScriptFromString:injection];
    }else{
        return nil;
    }
}

// 注入 js 核心代码
- (void)webViewDidStartLoad:(UIWebView *)webView{
    [self.realDelegate webViewDidStartLoad:webView];
    
    if (! self.javascriptInterfaces){
        self.javascriptInterfaces = [[NSMutableDictionary alloc] init];
    }
    
    NSMutableString* injection = [[NSMutableString alloc] init];
    
    //inject the javascript interface
// 利用动态运行时 获取类全部的方法 
    for(id key in self.javascriptInterfaces) {
        NSObject* interface = [self.javascriptInterfaces objectForKey:key];
        
        [injection appendString:@"EasyJS.inject(\""];
        [injection appendString:key];
        [injection appendString:@"\", ["];
        
        unsigned int mc = 0;
        Class cls = object_getClass(interface);
        Method * mlist = class_copyMethodList(cls, &mc);
        for (int i = 0; i < mc; i++){
            [injection appendString:@"\""];
            [injection appendString:[NSString stringWithUTF8String:sel_getName(method_getName(mlist[i]))]];
            [injection appendString:@"\""];
            
            if (i != mc - 1){
                [injection appendString:@", "];
            }
        }
        
        free(mlist);
        
        [injection appendString:@"]);"];
    }
    
    
    NSString* js = INJECT_JS;
    //inject the basic functions first
    [webView stringByEvaluatingJavaScriptFromString:js];
    //inject the function interface
    [webView stringByEvaluatingJavaScriptFromString:injection];
    
    [injection release];
}