WebViewJavascriptBridge 调用过程（三）

OC调用JS过程

与JS端调用OC基本思想一致
以WKWebView为例
1、JS端注册

        bridge.registerHandler('testJavascriptHandler', function(data, responseCallback) {
            log('ObjC called testJavascriptHandler with', data)
            var responseData = { 'Javascript Says':'Right back atcha!' }
            log('JS responding with', responseData)
            responseCallback(responseData)
        })
//实际调用
// 对应 原生端JS调用OC
    function registerHandler(handlerName, handler) {
        messageHandlers[handlerName] = handler;
    }

2、OC端调用

    [_bridge callHandler:@"testJavascriptHandler" data:data responseCallback:^(id response) {
        NSLog(@"testJavascriptHandler responded: %@", response);
    }];
// 实际调用 
- (void)sendData:(id)data responseCallback:(WVJBResponseCallback)responseCallback handlerName:(NSString*)handlerName {
    NSMutableDictionary* message = [NSMutableDictionary dictionary];
    
    if (data) {
        message[@"data"] = data;
    }
    // 同理 全局字典保存 
    if (responseCallback) {
        NSString* callbackId = [NSString stringWithFormat:@"objc_cb_%ld", ++_uniqueId];
        self.responseCallbacks[callbackId] = [responseCallback copy];
        message[@"callbackId"] = callbackId;
    }
    
    if (handlerName) {
        message[@"handlerName"] = handlerName;
    }
// message 为@{@"data":data,@"callbackId": callbackId,@"handlerName": handlerName}
    [self _queueMessage:message];
}

3、调用JS

- (void)_dispatchMessage:(WVJBMessage*)message {
    NSString *messageJSON = [self _serializeMessage:message pretty:NO];
    [self _log:@"SEND" json:messageJSON];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\\" withString:@"\\\\"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\"" withString:@"\\\""];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\'" withString:@"\\\'"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\n" withString:@"\\n"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\r" withString:@"\\r"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\f" withString:@"\\f"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\u2028" withString:@"\\u2028"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\u2029" withString:@"\\u2029"];
    
    NSString* javascriptCommand = [NSString stringWithFormat:@"WebViewJavascriptBridge._handleMessageFromObjC('%@');", messageJSON];
    if ([[NSThread currentThread] isMainThread]) {
        [self _evaluateJavascript:javascriptCommand];

    } else {
        dispatch_sync(dispatch_get_main_queue(), ^{
            [self _evaluateJavascript:javascriptCommand];
        });
    }
}

4、解析

        function _doDispatchMessageFromObjC() {
            var message = JSON.parse(messageJSON);
            var messageHandler;
            var responseCallback;
//不会走下面流程
/*
            if (message.responseId) {
                responseCallback = responseCallbacks[message.responseId];
                if (!responseCallback) {
                    return;
                }
                responseCallback(message.responseData);
                delete responseCallbacks[message.responseId];
            } else */
 {
              //同理 回传handlerName 和参数  再次回传  callbackResponseId 
                if (message.callbackId) {
                    var callbackResponseId = message.callbackId;
                    responseCallback = function(responseData) {
// 进入回调OC流程
                        _doSend({ handlerName:message.handlerName, responseId:callbackResponseId, responseData:responseData });
                    };
                }
                // 同理 执行保存的匿名函数 调用js的过程已经完结
                var handler = messageHandlers[message.handlerName];
                if (!handler) {
                    console.log("WebViewJavascriptBridge: WARNING: no handler for message from ObjC:", message);
                } else {
// 执行js方法 并且开始回调
                    handler(message.data, responseCallback);
                }
            }
        }
    }

5、OC端通过代理 处理回调

function _doSend(message, responseCallback) {
 // responseCallback为空 不走下面流程
/*
    if (responseCallback) {
            var callbackId = 'cb_'+(uniqueId++)+'_'+new Date().getTime();
            responseCallbacks[callbackId] = responseCallback;
            message['callbackId'] = callbackId;
        }
*/
// 此处的 message { handlerName:message.handlerName, responseId:callbackResponseId, responseData:responseData }
        sendMessageQueue.push(message);
        messagingIframe.src = CUSTOM_PROTOCOL_SCHEME + '://' + QUEUE_HAS_MESSAGE;
    }

6、OC端解析

// 同理 取出 JS端保存的  { handlerName:message.handlerName, responseId:callbackResponseId, responseData:responseData }
- (void)WKFlushMessageQueue {
    [_webView evaluateJavaScript:[_base webViewJavascriptFetchQueyCommand] completionHandler:^(NSString* result, NSError* error) {
        if (error != nil) {
            NSLog(@"WebViewJavascriptBridge: WARNING: Error when trying to fetch data from WKWebView: %@", error);
        }
        [_base flushMessageQueue:result];
    }];
}

7、核心方法 执行回调

- (void)flushMessageQueue:(NSString *)messageQueueString{
    if (messageQueueString == nil || messageQueueString.length == 0) {
        NSLog(@"WebViewJavascriptBridge: WARNING: ObjC got nil while fetching the message queue JSON from webview. This can happen if the WebViewJavascriptBridge JS is not currently present in the webview, e.g if the webview just loaded a new page.");
        return;
    }

    id messages = [self _deserializeMessageJSON:messageQueueString];
    for (WVJBMessage* message in messages) {
        if (![message isKindOfClass:[WVJBMessage class]]) {
            NSLog(@"WebViewJavascriptBridge: WARNING: Invalid %@ received: %@", [message class], message);
            continue;
        }
        [self _log:@"RCVD" json:message];
        
        NSString* responseId = message[@"responseId"];
        if (responseId) {
            WVJBResponseCallback responseCallback = _responseCallbacks[responseId];
            responseCallback(message[@"responseData"]);
            [self.responseCallbacks removeObjectForKey:responseId];
        }
//以下流程不会走 回调完成  整个OC调用js方法 完成
/* else {
            WVJBResponseCallback responseCallback = NULL;
            NSString* callbackId = message[@"callbackId"];
            if (callbackId) {
                responseCallback = ^(id responseData) {
                    if (responseData == nil) {
                        responseData = [NSNull null];
                    }
                    
                    WVJBMessage* msg = @{ @"responseId":callbackId, @"responseData":responseData };
                    [self _queueMessage:msg];
                };
            } else {
                responseCallback = ^(id ignoreResponseData) {
                    // Do nothing
                };
            }
            
            WVJBHandler handler = self.messageHandlers[message[@"handlerName"]];
            
            if (!handler) {
                NSLog(@"WVJBNoHandlerException, No handler for message from JS: %@", message);
                continue;
            }
            
            handler(message[@"data"], responseCallback);
        }
    }
*/
}