Cordova源码学习(二)-Native回调JS

本文只对JS与Native之间的交互进行源码阅读。至于Cordova如何开发插件等等，请参考Cordova官方文档：https://cordova.apache.org/docs/en/latest/

Native回调JS

流程图

解析

• Native
  Native方法执行完，通过sendPluginResult开始，回调结果给js

  • sendPluginResult:

    - (void)sendPluginResult:(CDVPluginResult*)result callbackId:(NSString*)callbackId
    {
        int status = [result.status intValue];
        BOOL keepCallback = [result.keepCallback boolValue];
        NSString* argumentsAsJSON = [result argumentsAsJSON];
        BOOL debug = NO;
        
        NSString* js = [NSString stringWithFormat:@"cordova.require('cordova/exec').nativeCallback('%@',%d,%@,%d, %d)", callbackId, status, argumentsAsJSON, keepCallback, debug];
    
        [self evalJsHelper:js];
    }

  • evalJsHelper:
    执行JS，这里的流程跟JS调Native执行JS一模一样的代码，利用UIWebView-stringByEvaluatingJavaScriptFromString:方法执行JS

    - (void)evalJsHelper2:(NSString*)js
    {
        [_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];
            }
        }];
    }

    • 其执行回调里仍然有处理命令队列的代码

• JS

  • nativeCallback
    这一步，并不是直接就回调结束了，还会通过nativeEvalAndFetch-nativeFetchMessages返回当前的commandQueue里的内容，会到前一步evaluateJavaScript执行结束的回调中，直到全部执行结束。触发cordova.callbackFromNative

    iOSExec.nativeCallback = function(callbackId, status, message, keepCallback, debug) {
        return iOSExec.nativeEvalAndFetch(function() {
            var success = status === 0 || status === 1;
            var args = convertMessageToArgsNativeToJs(message);
            function nc2() {
                cordova.callbackFromNative(callbackId, success, status, args, keepCallback);
            }
            setTimeout(nc2, 0);
        });
    };

  • callbackFromNative
    这里的源码注释也非常清楚了，根据Native返回的结果进行回调处理

    /**
    * Called by native code when returning the result from an action.
    */
    callbackFromNative: function(callbackId, isSuccess, status, args, keepCallback) {
        try {
            var callback = cordova.callbacks[callbackId];
            if (callback) {
                if (isSuccess && status == cordova.callbackStatus.OK) {
                    callback.success && callback.success.apply(null, args);
                } else if (!isSuccess) {
                    callback.fail && callback.fail.apply(null, args);
                }
                /*
                else
                    Note, this case is intentionally not caught.
                    this can happen if isSuccess is true, but callbackStatus is NO_RESULT
                    which is used to remove a callback from the list without calling the callbacks
                    typically keepCallback is false in this case
                */
                // Clear callback if not expecting any more results
                if (!keepCallback) {
                    delete cordova.callbacks[callbackId];
                }
            }
        }
        catch (err) {
            // ...
        }
    }

其他补充

• CDVViewController

  • 看构成，就知道CDVViewController是作为一个功能整合的类，这里面包含的命令队列、协议代理，在上面都已经有涉及
  • 内部主要初始化插件、配置、设置代理、处理生命周期

    @interface CDVViewController : UIViewController <CDVScreenOrientationDelegate>{
        @protected
        id <CDVWebViewEngineProtocol> _webViewEngine;
        @protected
        id <CDVCommandDelegate> _commandDelegate;
        @protected
        CDVCommandQueue* _commandQueue;
        NSString* _userAgent;
    }

• CDVUIWebViewEngine:CDVPlugin 以插件的形式实现

  • 成员变量engineWebView，创建webview，赋值engineWebView
  • pluginInitialize，初始化插件，设置代理。CDVUIWebViewNavigationDelegate代理在此处设置

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