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上一讲将主体流程和框架都已经介绍完了，
再次查看整个代码的时候，发现我还是有一些细节并没有列举出来，
例如之前只是介绍了addJavaScript一种方式实现通信，实际上还有另一种通信方式就是prompt方式，本讲再次介绍一下。
prompt有几个优势：
1.可以避免掉android 4.2以下，js安全问题
2.可以实现同步调用，直接返回值
下面开始分析代码逻辑：
重复的位置，不再累述。直接来到cordova.js中
define("cordova/android/nativeapiprovider", function(require, exports, module) {
var nativeApi = this._cordovaNative || require('cordova/android/promptbasednativeapi');//这里其实如果没有定义_cordovaNative就会走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方式的时候，方法都是一样的。
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]));//直接进入java端,代码片段1
},
setNativeToJsBridgeMode: function(bridgeSecret, value) {
prompt(value, 'gap_bridge_mode:' + bridgeSecret);
},
retrieveJsMessages: function(bridgeSecret, fromOnlineEvent) {
return prompt(+fromOnlineEvent, 'gap_poll:' + bridgeSecret);
}
};
});代码段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);//代码片段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;
}代码片段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);//执行与之前介绍的逻辑一样的流程中了
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;
}