開發Cordova插件如何保證callbackContext的活性

1、場景

開發一個cordova插件的時候，可能會遇到一個特別的action，需要調用後把java層獲得的值多次返回到上端JS中。但是cordova默認是調用一次callbackContext.error或者success就會不再對上端JS繼續傳輸數據

2、問題分析

查看源碼後得知 cordova做了這些操作：
1. java 層通過 callbackContext 將收集到的數據封裝進 PluginResult 類中
2. 再通過 toSuccessCallbackstring 或者 toErrorCallbackString 方法將封裝的數據傳遞到 JS 層並且調用
3. 最後根據 keepCallback 的參數，來調整 JS 端的 callback 是否保持活性

具體可以大概參考一下以下兩個代碼片段

public class PluginResult {
    //將callbackContext返回的數據封裝成一個JSON
    public String getJSONString() {
        return "{\"status\":" + this.status + ",\"message\":" + this.getMessage() + ",\"keepCallback\":" + this.keepCallback + "}";
    }

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

    //調用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實際調用的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.
     * 調用回調函數
     */
    callbackFromNative: function(callbackId, isSuccess, status, args, keepCallback) {
        try {
            //根據callbackId獲取是success還是error回調
            var callback = cordova.callbacks[callbackId];
            if (callback) {
                if (isSuccess && status == cordova.callbackStatus.OK) {
                    //調用success的函數
                    callback.success && callback.success.apply(null, args);
                } else if (!isSuccess) {
                    //調用error的函數
                    callback.fail && callback.fail.apply(null, args);
                }
                // Clear callback if not expecting any more results
                //如果keepCallback爲false，則回調一次立即停止(keepCallback默認是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、問題解決

我的思路是自定義一個customCallbackContext對原來的CallbackContext進行功能的擴展，以下我自定義的CustomCallbackContext.java，重點可以看sendPluginResult方法。
外部調用只需要調用callbackContext.success("msg",true)，便可以一直保持JS端接口的活性，調用callbackContext.success("msg",false)或callbackContext.success("msg")就可以使用執行一次就失活的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);
        }
        //重寫sendPluginResult方法，添加是否保持活性的參數
        public void sendPluginResult(PluginResult pluginResult, boolean isKeep) {
            //最關鍵的地方，給pluginResult設置是否保證活性
            pluginResult.setKeepCallback(isKeep);
            super.sendPluginResult(pluginResult);
        }

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

        /**
         * success回調,isKeep 爲true的時候,可以持續把數據返回到js層中
         *
         * @param message
         * @param isKeep
         */
        public void success(JSONObject message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK, message), isKeep);
        }

        /**
         * success回調,isKeep 爲true的時候,可以持續把數據返回到js層中
         *
         * @param message
         * @param isKeep
         */
        public void success(String message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK, message), isKeep);
        }

        /**
         * success回調,isKeep 爲true的時候,可以持續把數據返回到js層中
         *
         * @param message
         * @param isKeep
         */
        public void success(JSONArray message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK, message), isKeep);
        }

        /**
         * success回調,isKeep 爲true的時候,可以持續把數據返回到js層中
         *
         * @param message
         * @param isKeep
         */
        public void success(byte[] message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK, message), isKeep);
        }

        /**
         * success回調,isKeep 爲true的時候,可以持續把數據返回到js層中
         *
         * @param message
         * @param isKeep
         */
        public void success(int message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK, message), isKeep);
        }

        /**
         * success回調,isKeep 爲true的時候,可以持續把數據返回到js層中
         *
         * @param isKeep
         */
        public void success(boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.OK), isKeep);
        }

        /**
         * error回調,isKeep 爲true的時候,可以持續把數據返回到js層中
         *
         * @param message
         * @param isKeep
         */
        public void error(JSONObject message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.ERROR, message), isKeep);
        }

        /**
         * error回調,isKeep 爲true的時候,可以持續把數據返回到js層中
         *
         * @param message
         * @param isKeep
         */
        public void error(String message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.ERROR, message), isKeep);
        }

        /**
         * error回調,isKeep 爲true的時候,可以持續把數據返回到js層中
         *
         * @param message
         * @param isKeep
         */
        public void error(int message, boolean isKeep) {
            sendPluginResult(new PluginResult(PluginResult.Status.ERROR, message), isKeep);
        }
    }