cordova IOS源码浅析

cordova封装了一套js和OC通信的代码，cordova.js下的iOSExex是关键的js去调原生的发起点。

function iOSExec() {

    var successCallback, failCallback, service, action, actionArgs;
    var callbackId = null;
    if (typeof arguments[0] !== 'string') {
        // FORMAT ONE
        successCallback = arguments[0];
        failCallback = arguments[1];
        service = arguments[2];
        action = arguments[3];
        actionArgs = arguments[4];

        // Since we need to maintain backwards compatibility, we have to pass
        // an invalid callbackId even if no callback was provided since plugins
        // will be expecting it. The Cordova.exec() implementation allocates
        // an invalid callbackId and passes it even if no callbacks were given.
        callbackId = 'INVALID';
    } else {
        throw new Error('The old format of this exec call has been removed (deprecated since 2.1). Change to: ' +
            'cordova.exec(null, null, \'Service\', \'action\', [ arg1, arg2 ]);'
        );
    }

    // If actionArgs is not provided, default to an empty array
    actionArgs = actionArgs || [];

    // Register the callbacks and add the callbackId to the positional
    // arguments if given.
    if (successCallback || failCallback) {
        callbackId = service + cordova.callbackId++;
        cordova.callbacks[callbackId] =
            {success:successCallback, fail:failCallback};
    }

    actionArgs = massageArgsJsToNative(actionArgs);

    var command = [callbackId, service, action, actionArgs];

    // Stringify and queue the command. We stringify to command now to
    // effectively clone the command arguments in case they are mutated before
    // the command is executed.
    commandQueue.push(JSON.stringify(command));

    // If we're in the context of a stringByEvaluatingJavaScriptFromString call,
    // then the queue will be flushed when it returns; no need for a poke.
    // Also, if there is already a command in the queue, then we've already
    // poked the native side, so there is no reason to do so again.
    if (!isInContextOfEvalJs && commandQueue.length == 1) {
        pokeNative();
    }
}

OC里执行js很简单，就是evaluateJavaScript:js方法，执行js的地方最后都走到evalJsHelper2这里

- (void)evalJsHelper2:(NSString*)js
{
    CDV_EXEC_LOG(@"Exec: evalling: %@", [js substringToIndex:MIN([js length], 160)]);
    [_viewController.webViewEngine evaluateJavaScript:js completionHandler:^(id obj, NSError* error) {
        // TODO: obj can be something other than string
        if ([obj isKindOfClass:[NSString class]]) {
            NSString* commandsJSON = (NSString*)obj;
            if ([commandsJSON length] > 0) {
                CDV_EXEC_LOG(@"Exec: Retrieved new exec messages by chaining.");
            }

            [_commandQueue enqueueCommandBatch:commandsJSON];
            [_commandQueue executePending];
        }
    }];
}

可以看到就是evaluateJavaScript方法去执行一段js。

　　下面具体来看一下：

　1.首先一个插件肯定在js里去调用，其实都是走exec这个方法，具体是走iOSExec(),还是androidExec(),对应各自平台。

　　　iOSExec在上面已经粘贴了，最下面有个pokeNative()，看方法名也猜出来是去调native端的代码

function pokeNative() {
  　　...
       execIframe.contentWindow.location = 'gap://ready';
　　　...
}

　　前面js通过创建一个iframe并发送gap://ready这个指令来告诉native开始执行操作。

　　（ios在7.0以前没有提供js直接调OC的代码，所以通过下面这种方式url截取。在7.0以后版本的JavaScriptCore就可　　以,http://blog.csdn.net/j_akill/article/details/44463301）

　　native中对应的操作在CDVUIWebViewNavigationDelegate.m(老的cordova好像再CDVViewController.m下面)文件中的webView:shouldStartLoadWithRequest:navigationType:方法

　　

- (BOOL)webView:(UIWebView*)theWebView shouldStartLoadWithRequest:(NSURLRequest*)request navigationType:(UIWebViewNavigationType)navigationType
{
    NSURL* url = [request URL];
    CDVViewController* vc = (CDVViewController*)self.enginePlugin.viewController;

    /*
     * Execute any commands queued with cordova.exec() on the JS side.
     * The part of the URL after gap:// is irrelevant.
     */
    if ([[url scheme] isEqualToString:@"gap"]) {
        [vc.commandQueue fetchCommandsFromJs];
        // The delegate is called asynchronously in this case, so we don't have to use
        // flushCommandQueueWithDelayedJs (setTimeout(0)) as we do with hash changes.
        [vc.commandQueue executePending];
        return NO;
    }

    /*
     * Give plugins the chance to handle the url
     */
    BOOL anyPluginsResponded = NO;
    BOOL shouldAllowRequest = NO;

    for (NSString* pluginName in vc.pluginObjects) {
        CDVPlugin* plugin = [vc.pluginObjects objectForKey:pluginName];
        SEL selector = NSSelectorFromString(@"shouldOverrideLoadWithRequest:navigationType:");
        if ([plugin respondsToSelector:selector]) {
            anyPluginsResponded = YES;
            shouldAllowRequest = (((BOOL (*)(id, SEL, id, int))objc_msgSend)(plugin, selector, request, navigationType));
            if (!shouldAllowRequest) {
                break;
            }
        }
    }

    if (anyPluginsResponded) {
        return shouldAllowRequest;
    }

    /*
     * Handle all other types of urls (tel:, sms:), and requests to load a url in the main webview.
     */
    BOOL shouldAllowNavigation = [self defaultResourcePolicyForURL:url];
    if (shouldAllowNavigation) {
        return YES;
    } else {
        [[NSNotificationCenter defaultCenter] postNotification:[NSNotification notificationWithName:CDVPluginHandleOpenURLNotification object:url]];
    }

    return NO;
}

　　到这就是js调用native的过程了。

　　　　

　　

另外：

CDVAvailability.h里有个宏 

// Enable this to log all exec() calls.

#define CDV_ENABLE_EXEC_LOGGING 0

设置为1，把所有执行exec的log打出来，就看到所有执行js的地方