开发Cordova插件如何保证callbackContext的活性

1、场景

开发一个cordova插件的时候，可能会遇到一个特别的action，需要调用后把java层获得的值多次返回到上端JS中。但是cordova默认是调用一次callbackContext.error或者success就会不再对上端JS继续传输数据

2、问题分析

查看源码后得知 cordova做了这些操作：
1. java 层通过 callbackContext 将收集到的数据封装进 PluginResult 类中
2. 再通过 toSuccessCallbackstring 或者 toErrorCallbackString 方法将封装的数据传递到 JS 层并且调用
3. 最后根据 keepCallback 的参数，来调整 JS 端的 callback 是否保持活性

具体可以大概参考一下以下两个代码片段

public class PluginResult {
    //将callbackContext返回的数据封装成一个JSON
    public String getJSONString() {
        return "{\"status\":" + this.status + ",\"message\":" + this.getMessage() + ",\"keepCallback\":" + this.keepCallback + "}";
    }

     //调用cordova.js文件中的callbackSuccess方法
     public String toSuccessCallbackString(String callbackId) {
        return "cordova.callbackSuccess('"+callbackId+"',"+this.getJSONString()+");";
    }

    //调用cordova.js文件中的callbackError方法
    public String toErrorCallbackString(String callbackId) {
        return "cordova.callbackError('"+callbackId+"', " + this.getJSONString()+ ");";
    }
}

cordova.js

var cordova = {
    /**
     * Called by native code when returning successful result from an action.
     * PluginResult.java中toSuccessCallbackString实际调用的js方法
     */
    callbackSuccess: function(callbackId, args) {
        cordova.callbackFromNative(callbackId, true, args.status, [args.message], args.keepCallback);
    },

    /**
     * Called by native code when returning error result from an action.
     */
    callbackError: function(callbackId, args) {
        // TODO: Deprecate callbackSuccess and callbackError in favour of callbackFromNative.
        // Derive success from status.
        cordova.callbackFromNative(callbackId, false, args.status, [args.message], args.keepCallback);
    },

    /**
     * Called by native code when returning the result from an action.
     * 调用回调函数
     */
    callbackFromNative: function(callbackId, isSuccess, status, args, keepCallback) {
        try {
            //根据callbackId获取是success还是error回调
            var callback = cordova.callbacks[callbackId];
            if (callback) {
                if (isSuccess && status == cordova.callbackStatus.OK) {
                    //调用success的函数
                    callback.success && callback.success.apply(null, args);
                } else if (!isSuccess) {
                    //调用error的函数
                    callback.fail && callback.fail.apply(null, args);
                }
                // Clear callback if not expecting any more results
                //如果keepCallback为false，则回调一次立即停止(keepCallback默认是false)
                if (!keepCallback) {
                    delete cordova.callbacks[callbackId];
                }
            }
        }
        catch (err) {
            var msg = "Error in " + (isSuccess ? "Success" : "Error") + " callbackId: " + callbackId + " : " + err;
            console && console.log && console.log(msg);
            cordova.fireWindowEvent("cordovacallbackerror", { 'message': msg });
            throw err;
        }
    },
};

3、问题解决

我的思路是自定义一个customCallbackContext对原来的CallbackContext进行功能的扩展，以下我自定义的CustomCallbackContext.java，重点可以看sendPluginResult方法。
外部调用只需要调用callbackContext.success("msg",true)，便可以一直保持JS端接口的活性，调用callbackContext.success("msg",false)或callbackContext.success("msg")就可以使用执行一次就失活的callback

    protected static class CustomCallbackContext extends CallbackContext {


        public static CustomCallbackContext newInstance(CallbackContext callbackContext) {
            CordovaWebView webView = null;
            Class cls = callbackContext.getClass();
            try {
                Field field = cls.getDeclaredField("webView");
                field.setAccessible(true);
                webView = (CordovaWebView) field.get(callbackContext);
            } catch (NoSuchFieldException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
            return new CustomCallbackContext(callbackContext.getCallbackId(), webView);
        }

        public CustomCallbackContext(String callbackId, CordovaWebView webView) {
            super(callbackId, webView);
        }
        //重写sendPluginResult方法，添加是否保持活性的参数
        public void sendPluginResult(PluginResult pluginResult, boolean isKeep) {
            //最关键的地方，给pluginResult设置是否保证活性
            pluginResult.setKeepCallback(isKeep);
            super.sendPluginResult(pluginResult);
        }

        /********************以下是模仿CallbackContext写的success和error方法*************************/

        /**
         * success回调,isKeep 为true的时候,可以持续把数据返回到js层中
         *
         * @param message
         * @param isKeep
         */
        public void success(JSONObject message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK, message), isKeep);
        }

        /**
         * success回调,isKeep 为true的时候,可以持续把数据返回到js层中
         *
         * @param message
         * @param isKeep
         */
        public void success(String message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK, message), isKeep);
        }

        /**
         * success回调,isKeep 为true的时候,可以持续把数据返回到js层中
         *
         * @param message
         * @param isKeep
         */
        public void success(JSONArray message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK, message), isKeep);
        }

        /**
         * success回调,isKeep 为true的时候,可以持续把数据返回到js层中
         *
         * @param message
         * @param isKeep
         */
        public void success(byte[] message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK, message), isKeep);
        }

        /**
         * success回调,isKeep 为true的时候,可以持续把数据返回到js层中
         *
         * @param message
         * @param isKeep
         */
        public void success(int message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK, message), isKeep);
        }

        /**
         * success回调,isKeep 为true的时候,可以持续把数据返回到js层中
         *
         * @param isKeep
         */
        public void success(boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK), isKeep);
        }

        /**
         * error回调,isKeep 为true的时候,可以持续把数据返回到js层中
         *
         * @param message
         * @param isKeep
         */
        public void error(JSONObject message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.ERROR, message), isKeep);
        }

        /**
         * error回调,isKeep 为true的时候,可以持续把数据返回到js层中
         *
         * @param message
         * @param isKeep
         */
        public void error(String message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.ERROR, message), isKeep);
        }

        /**
         * error回调,isKeep 为true的时候,可以持续把数据返回到js层中
         *
         * @param message
         * @param isKeep
         */
        public void error(int message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.ERROR, message), isKeep);
        }
    }