上一講將主體流程和框架都已經介紹完了，

再次檢視整個程式碼的時候，發現我還是有一些細節並沒有列舉出來，

例如之前只是介紹了addJavaScript一種方式實現通訊，實際上還有另一種通訊方式就是prompt方式，本講再次介紹一下。

prompt有幾個優勢：

1.可以避免掉android 4.2以下，js安全問題

2.可以實現同步呼叫，直接返回值

下面開始分析程式碼邏輯：

重複的位置，不再累述。直接來到cordova.js中

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

var nativeApi = this._cordovaNative || require('cordova/android/promptbasednativeapi');//這裡其實如果沒有定義_cordovaNative就會走prompt
var currentApi = nativeApi;

module.exports = {
    get: function() { return currentApi; },
    setPreferPrompt: function(value) {
        currentApi = value ? require('cordova/android/promptbasednativeapi') : nativeApi;
    },
    // Used only by tests.
    set: function(value) {
        currentApi = value;
    }
};

});
 

而在使用prompt方式的時候，方法都是一樣的。

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

module.exports = {
    exec: function(bridgeSecret, service, action, callbackId, argsJson) {
        return prompt(argsJson, 'gap:'+JSON.stringify([bridgeSecret, service, action, callbackId]));//直接進入java端,程式碼片段1
    },
    setNativeToJsBridgeMode: function(bridgeSecret, value) {
        prompt(value, 'gap_bridge_mode:' + bridgeSecret);
    },
    retrieveJsMessages: function(bridgeSecret, fromOnlineEvent) {
        return prompt(+fromOnlineEvent, 'gap_poll:' + bridgeSecret);
    }
};

});
 

程式碼段1：SystemWebChromeClient.java

    @Override
    public boolean onJsPrompt(WebView view, String origin, String message, String defaultValue, final JsPromptResult result) {
        // Unlike the @JavascriptInterface bridge, this method is always called on the UI thread.
        String handledRet = parentEngine.bridge.promptOnJsPrompt(origin, message, defaultValue);//程式碼片段2
        if (handledRet != null) {
            result.confirm(handledRet);
        } else {
            dialogsHelper.showPrompt(message, defaultValue, new CordovaDialogsHelper.Result() {
                @Override
                public void gotResult(boolean success, String value) {
                    if (success) {
                        result.confirm(value);
                    } else {
                        result.cancel();
                    }
                }
            });
        }
        return true;
    }
 

程式碼片段2：CordovaBridge.java

    public String promptOnJsPrompt(String origin, String message, String defaultValue) {
        if (defaultValue != null && defaultValue.length() > 3 && defaultValue.startsWith("gap:")) {
            JSONArray array;
            try {
                array = new JSONArray(defaultValue.substring(4));
                int bridgeSecret = array.getInt(0);
                String service = array.getString(1);
                String action = array.getString(2);
                String callbackId = array.getString(3);
                String r = jsExec(bridgeSecret, service, action, callbackId, message);//執行與之前介紹的邏輯一樣的流程中了
                return r == null ? "" : r;
            } catch (JSONException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
            return "";
        }
        // Sets the native->JS bridge mode.
        else if (defaultValue != null && defaultValue.startsWith("gap_bridge_mode:")) {
            try {
                int bridgeSecret = Integer.parseInt(defaultValue.substring(16));
                jsSetNativeToJsBridgeMode(bridgeSecret, Integer.parseInt(message));
            } catch (NumberFormatException e){
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
            return "";
        }
        // Polling for JavaScript messages
        else if (defaultValue != null && defaultValue.startsWith("gap_poll:")) {
            int bridgeSecret = Integer.parseInt(defaultValue.substring(9));
            try {
                String r = jsRetrieveJsMessages(bridgeSecret, "1".equals(message));
                return r == null ? "" : r;
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
            return "";
        }
        else if (defaultValue != null && defaultValue.startsWith("gap_init:")) {
            // Protect against random iframes being able to talk through the bridge.
            // Trust only pages which the app would have been allowed to navigate to anyway.
            if (pluginManager.shouldAllowBridgeAccess(origin)) {
                // Enable the bridge
                int bridgeMode = Integer.parseInt(defaultValue.substring(9));
                jsMessageQueue.setBridgeMode(bridgeMode);
                // Tell JS the bridge secret.
                int secret = generateBridgeSecret();
                return ""+secret;
            } else {
                LOG.e(LOG_TAG, "gap_init called from restricted origin: " + origin);
            }
            return "";
        }
        return null;
    }