iOS版PhoneGap原理分析

/*
* 方法的返回值是BOOL值。
* 返回YES：表示让浏览器执行默认操作，比如某个a链接跳转
* 返回NO：表示不执行浏览器的默认操作，这里因为通过url协议来判断js执行native的操作，肯定不是浏览器默认操作，故返回NO
* /
- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType {
    NSURL *url = [request URL];
    if ([[url scheme] isEqualToString:@"callFunction") {
        //调用原生方法

        return NO;
    } else if (([[url scheme] isEqualToString:@"sendEvent") {
        //触发事件

        return NO;
    } else {
        return YES;
    }
}

function alertDismissed() {
    // do something
}

function showAlert() {
    cordova.require("cordova/plugin/notification").alert(
        ‘You are the winner!‘,  // message
        alertDismissed,         // callback
        ‘Game Over‘,            // title
        ‘Done‘                  // buttonName
    );
}

var exec = cordova.require(‘cordova/exec‘);
var platform = cordova.require(‘cordova/platform‘);

module.exports = {

    /**
     * Open a native alert dialog, with a customizable title and button text.
     *
     * @param {String} message              Message to print in the body of the alert
     * @param {Function} completeCallback   The callback that is called when user clicks on a button.
     * @param {String} title                Title of the alert dialog (default: Alert)
     * @param {String} buttonLabel          Label of the close button (default: OK)
     */
    alert: function(message, completeCallback, title, buttonLabel) {
        var _title = (title || "Alert");
        var _buttonLabel = (buttonLabel || "OK");
        exec(completeCallback, null, "Notification", "alert", [message, _title, _buttonLabel]);
    }
}

....

define("cordova/exec", function(require, exports, module) {

    ...

    function iOSExec() {
        ...

        var successCallback, failCallback, service, action, actionArgs, splitCommand;
        var callbackId = null;

        ...

        // 格式化传入参数
        successCallback = arguments[0]; //成功的回调函数
        failCallback = arguments[1];    //失败的回调函数
        service = arguments[2];         //表示调用native类的类名
        action = arguments[3];          //表示调用native类的一个方法
        actionArgs = arguments[4];      //参数

        //默认callbackId为‘INVALID‘，表示不需要回调
        callbackId = ‘INVALID‘;

        ...

        //如果传入参数有successCallback或failCallback，说明需要回调，就设置callbackId，并存储对应的回调函数
        if (successCallback || failCallback) {
            callbackId = service + cordova.callbackId++;
            cordova.callbacks[callbackId] =
                {success:successCallback, fail:failCallback};
        }

        //格式化传入的service、action、actionArgs，并存储，准备native代码来调用
        actionArgs = massageArgsJsToNative(actionArgs);

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

        commandQueue.push(JSON.stringify(command));

        ...

        //通过创建一个iframe并设置src，给native代码一个指令，开始执行js调用native的过程
        execIframe = execIframe || createExecIframe();
        if (!execIframe.contentWindow) {
            execIframe = createExecIframe();
        }
        execIframe.src = "gap://ready";

        ...
    }

    module.exports = iOSExec;

});

- (BOOL)webView:(UIWebView*)theWebView shouldStartLoadWithRequest:(NSURLRequest*)request navigationType:(UIWebViewNavigationType)navigationType
{
    NSURL* url = [request URL];

    /*
     * 判断url的协议以"gap"开头
     * 执行在js端调用cordova.exec()的command队列
     * 注：这里的command表示js调用native
     */
    if ([[url scheme] isElaqualToString:@"gap"]) {
       //_commandQueue即CDVCommandQueue类
        //从js端拉取command，即存储在js端commandQueue数组中的数据
        [_commandQueue fetchCommandsFromJs];
        //开始执行command
        [_commandQueue executePending];
        return NO;
    }
...
}

- (void)fetchCommandsFromJs
{
    // 获取js端存储的command，并在native暂存
    NSString* queuedCommandsJSON = [_viewController.webView stringByEvaluatingJavaScriptFromString:
        @"cordova.require(‘cordova/exec‘).nativeFetchMessages()"];
    [self enqueueCommandBatch:queuedCommandsJSON];
}

- (void)executePending
{
    ...
    //_queue即command队列，依次执行
    while ([_queue count] > 0) {
        ...
        //取出从js中获取的command字符串，解析为native端的CDVInvokedUrlCommand类
        CDVInvokedUrlCommand* command = [CDVInvokedUrlCommand commandFromJson:jsonEntry];
        ...
        //执行command
        [self execute:command])
        ...
    }
}

- (BOOL)execute:(CDVInvokedUrlCommand*)command
{
    ...
    BOOL retVal = YES;
    //获取plugin对应的实例
    CDVPlugin* obj = [_viewController.commandDelegate getCommandInstance:command.className];
    //调用plugin实例的方法名
    NSString* methodName = [NSString stringWithFormat:@"%@:", command.methodName];
    SEL normalSelector = NSSelectorFromString(methodName);
    if ([obj respondsToSelector:normalSelector]) {
        //消息发送，执行plugin实例对应的方法，并传递参数
        objc_msgSend(obj, normalSelector, command);
    } else {
        // There‘s no method to call, so throw an error.
        NSLog(@"ERROR: Method ‘%@‘ not defined in Plugin ‘%@‘", methodName, command.className);
        retVal = NO;
    }
    ...
    return retVal;
}

- (void)alert:(CDVInvokedUrlCommand*)command
{
    NSString* callbackId = command.callbackId;
    NSString* message = [command argumentAtIndex:0];
    NSString* title = [command argumentAtIndex:1];
    NSString* buttons = [command argumentAtIndex:2];

    [self showDialogWithMessage:message title:title buttons:@[buttons] defaultText:nil callbackId:callbackId dialogType:DIALOG_TYPE_ALERT];
}