Develop Reference

Call Wicket 6 Code from Javascript and return value

I have managed to call my Wicket 6 Java code from Javascript using option A in this example: https://stackoverflow.com/a/42612027/1047418
However, I have not been able to find examples for returning data from the Java side back to JavaScript (the generated JavaScript callback function does not even include a return statement). How can this be achieved?
Edit: I am not trying to set an attribute in Java and as I've already explained, calling Wicket from JavaScript is not the problem here. I am trying to return a JSON object from Wicket back to the browser as a result of an Ajax request.
Edit2: Following martin-g's examples I cobbled up this working example...
Java
public class MyAjaxBehaviour extends AbstractDefaultAjaxBehavior {
#Override
protected void onComponentTag(ComponentTag tag) {
super.onComponentTag(tag);
tag.put("aprachatcallbackurl", getCallbackUrl());
}
#Override
protected void updateAjaxAttributes(AjaxRequestAttributes attributes) {
super.updateAjaxAttributes(attributes);
attributes.setDataType("json");
attributes.setWicketAjaxResponse(false);
}
#Override
protected void respond(AjaxRequestTarget target) {
getComponent().getRequestCycle().replaceAllRequestHandlers(
new TextRequestHandler("application/json", "UTF-8", "{...JSON GOES HERE...}));
}
}
JavaScript
var mySuccessCallback = function(param1, param2, data, statusText) {
// Data contains the parsed JSON object from MyAjaxBehaviour.respond(...)
...
}
var myFailureCallback = function() {
...
}
Wicket.Ajax.get({
"u": callbackUrl,
"dt": "json",
"wr": false,
"sh": [mySuccessCallback],
"fh": [myFailureCallback]
});
Main problem as that the Wicket 7 Reference incorrectly instructs to use "wr" instead of "dt" in the JavaScript call. :)

I think you can do it in a simpler way!
Wicket Ajax API is just: Wicket.Ajax.ajax({...}). All you need to prepare at the server side is to save the callback url, e.g. by saving it globally in the window object or in HTML element's attributes (data-the-url).
public class CallFromJavascriptBehavior extends AbstractDefaultAjaxBehavior {
#Override
protected void respond(AjaxRequestTarget target) {
final StringValue parameterValue = RequestCycle.get().getRequest().getQueryParameters().getParameterValue("yourName");
System.out.println(String.format("Hello %s", parameterValue.toString()));
// write anything to the WebResponse and then consume it in the JS success handler. See below
}
#Override
public void onComponenntTag(ComponenntTag tag, Component component) {
super.onComponenntTag(tag, component);
tag.put("data-the-url", getCallbackUrl());
}
}
Then in your JS code you can do:
var callbackUrl = jQuery("#theElementId").data("the-url");
Wicket.Ajax.get({"u": callbackUrl, "sh":[successHandler], "fh": [failureHandler] });
Where successHandler and failureHandler are JS functions defined inline (e.g. function(...) {}) or elsewhere.
More documentation you can find at:
https://ci.apache.org/projects/wicket/guide/7.x/single.html#_ajax_request_attributes_and_call_listeners
A blog article with an complete example at http://wicketinaction.com/2012/07/wicket-6-javascript-improvements/

You can just write a Resource and mount it, and get it with your favorite Ajax-approach.
For example:
public class MyResource extends AbstractResource
#Override
protected ResourceResponse newResourceResponse( Attributes attributes )
{
ResourceResponse resourceResponse = new ResourceResponse();
resourceResponse.setContentType( "text/json" );
resourceResponse.setTextEncoding( "utf-8" );
HttpServletRequest request = (HttpServletRequest) attributes.getRequest().getContainerRequest();
try
{
this.json = IOUtils.toString( request.getInputStream() );
}
catch ( IOException e )
{
e.printStackTrace();
}
resourceResponse.setWriteCallback( new WriteCallback()
{
#Override
public void writeData( Attributes attributes ) throws IOException
{
OutputStream outputStream = attributes.getResponse().getOutputStream();
Writer writer = new OutputStreamWriter( outputStream );
writer.write( MyResource.this.json );
writer.close();
}
} );
return resourceResponse;
}
(Copied from my other answer here https://stackoverflow.com/a/17876029/461499)
And see here for mounting it:
https://dzone.com/articles/how-implement-rss-feeds-custom

How can I call a server side c# method via javascript without a WebMethod or Updatepanel?

I would prefer not to use an update panel and using the common WebMethod approach leads me to this error with this code
private string currentHtml() {
StringWriter str_wrt = new StringWriter();
HtmlTextWriter html_wrt = new HtmlTextWriter(str_wrt);
Page.RenderControl(html_wrt);
return str_wrt.ToString();
}
[WebMethod]
public static void EmailPtoRequest() {
string test = currentHtml();
}
Error 8 An object reference is required for the non-static field, method, or property 'PtoRequest.cs.WebForm1.currentHtml()
Clearly the method being static is causing a bunch of headaches.
Is there a standard that I can use for this type of functionality? The goal is to allow the user to send their data to the server without causing a post and refreshing the page.
Note: I DO NOT want to use a webmethod as it is causing an error which does not let me compile.
public partial class WebForm1 : System.Web.UI.Page {
protected void Page_Load(object sender, EventArgs e) {
}
private string currentHtml() {
StringWriter str_wrt = new StringWriter();
HtmlTextWriter html_wrt = new HtmlTextWriter(str_wrt);
Page.RenderControl(html_wrt);
return str_wrt.ToString();
}
[WebMethod]
public static void EmailPtoRequest() {
WebForm1 WebForm1 = new WebForm1();
string test = WebForm1.currentHtml();
}
}
Results in 'test' being an empty string instead of the html of the page.
private static string currentHtml() {
StringWriter str_wrt = new StringWriter();
HtmlTextWriter html_wrt = new HtmlTextWriter(str_wrt);
Page.RenderControl(html_wrt);
return str_wrt.ToString();
}
[WebMethod]
public static void EmailPtoRequest() {
string test = currentHtml();
}
}
Results in the first error again, but in the currentHtml method instead.
Please remember the question is not about the error, but an alternative to webmethod or update panels. Thank you.

3 options:
Make the currentHtml method static,
Instantiate the class that contains currentHtml like this:
new MyClass().currentHtml();
Use an ajax enabled wcf service.

Unable To Insert An Array Selection into a Database

First off, I would just like to mention that my problem isn't as easy as the title suggests. Here is my problem. Basically I am trying to set the value of a string to a randomly selected item in a string array. Shown here:
String[] array = getResources().getStringArray(R.array.states);
selected_state = array[new Random().nextInt(array.length)];
When a button is pushed, this string is insert into my database. Like this:
long id = database_helper.insertData(selected_state);
It seem like it should work, but unfortunately for me it does not. Apparently selected_state is null when I try to insert it. But another string in my app that is pulled from an editText and inserted the exact same way is totally fine. Here are the relevant parts of my code:
public class my_class extends Fragment implements View.OnClickListener {
View rootView;
Button bing;
EditText text;
public String selected_state;
public String TEXT;
DatabaseAdapter database_helper;
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.my_fragment, container, false);
bing = (Button) rootView.findViewById(R.id.my_btn);
text = (EditText) rootView.findViewById(R.id.my_text_edit);
String[] array = getResources().getStringArray(R.array.states);
selected_state = array[new Random().nextInt(array.length)];
bing.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
send();
}
private void send() {
TEXT = text.getText().toString();
//VALUE HOLDS UP TO HERE
long id = database_helper.insertData(TEXT, selected_state);//NULL!!!!!!
if(id<0){
Toast.makeText(getActivity(), "SHES STUCK", Toast.LENGTH_LONG).show();
}else{
Toast.makeText(getActivity(), "SHES IN", Toast.LENGTH_LONG).show();
text.setText("");
}
}
});
return rootView;
}
#Override
public void onClick(View v) {
}
}
Thanks everyone!
EDIT The string (or what I believe to be a string) value has been carried down to the same place TEXT is. Marked above

WebViewClient not called the second time

I have a WebView which I use to load some html content locally in my app. It first loads the content, then calls a JavaScript function which then scrolls the WebView to a particular position.
The following code illustrates how I do this:
public class MyActivity extends Activity {
private WebView web1;
private int ID;
private MyWebViewClient webViewClient1;
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity);
// Get the ID of the law to be loaded.
ID = getIntent().getIntExtra("element_id", 1);
web1 = (WebView) findViewById(R.id.web1);
web1.getSettings().setJavaScriptEnabled(true);
// Initialize the webViewClients.
webViewClient1 = new MyWebViewClient(true);
web1.setWebViewClient(webViewClient1);
displayArticle(web1);
}
private void displayArticle (WebView wv) {
StringBuilder sb = new StringBuilder();
// Code to build the HTML String.
String finalHtml = sb.toString();
wv.loadDataWithBaseURL("file:///android_asset/html/", finalHtml, "text/html", "UTF-8", null);
}
private class MyWebViewClient extends WebViewClient {
String urlToLoad;
MyWebViewClient (boolean setUrlToLoad) {
if (setUrlToLoad) {
setUrlToLoad();
}
}
public void setUrlToLoad () {
this.urlToLoad = "javascript:(function () {" +
"var elem = document.getElementById('e"+ID+"');" +
"var x = 0;" +
"var y = 0;" +
"while (elem != null) {" +
"x += elem.offsetLeft;" +
"y += elem.offsetTop;" +
"elem = elem.offsetParent;" +
"}" +
"window.scrollTo(x, y);" +
"})()";
}
#Override
public void onPageStarted (WebView view, String url, Bitmap favicon) {
super.onPageStarted(view, url, favicon);
Log.d("Pages", "Page loading started");
}
#Override
public void onReceivedError (WebView view, int errorCode, String description, String failingUrl) {
super.onReceivedError(view, errorCode, description, failingUrl);
Log.d("Pages", "Webview content load error");
}
#Override
public void onPageFinished (WebView view, String url) {
super.onPageFinished(view, url);
Log.d("Pages", "Page loading finished");
if (urlToLoad != null) {
// Scroll to the position.
view.loadUrl(urlToLoad);
urlToLoad = null;
}
}
}
}
In the above code, the callback functions in the MyWebViewClient class are called for the first request using wv.loadDataWithBaseURL in the displayArticle(WebView wv) function, but when the request is finished and onPageFinished is called, the view.loadUrl(urlToLoad); call does not invoke another set of callbacks from MyWebViewClient. I am not quite sure why since it must be the same WebView I originally used and it should have the same instance of MyWebViewClient set.
Moreover, there are other loadUrl calls that I make with the same WebView, and this behaviour persists.
I would really appreciate if someone could explain why this happens.

loadUrl("javascript:...") is a bit of a special case: it evaluates the JavaScript code in the current page's context (just like <a href='javascript:...'>clicky</a> would) and therefore you won't get onPageStarted/onPageFinished callbacks.

Android Phonegap: Notify javascript when an AsyncTask is finished

in my app, when user click on a button in webview, a phonegap plugin will be called to trigger an asynctask to download file from internet. Now i want to send a signal back to javascript part when the asynctask is finished. But i don't know how to do it, because my plugin had already send something back before the asynctask is finished. Does anyone know how i can notify my javascript part without plugin in Phonegap?

I also asked this question in Phonegap Google Group, here is response of Simon Mac Donald. It works perfectly for me:
You can handle this situation by using the Plugin API quite easily. It
is implemented in the core API items Connection and Battery. What you
need to do is:
1) In your execute() method of your plugin save the callbackId you get.
2) Return a NO_RESULT plugin result and set keep callback id to true.
PluginResult pluginResult = new PluginResult(PluginResult.Status.NO_RESULT);
pluginResult.setKeepCallback(true);
return pluginResult;
3) When you async java method finishes return another plugin result like this:
PluginResult result = new PluginResult(PluginResult.Status.OK, data);
result.setKeepCallback(false);
this.success(result, this.myCallbackId);
As I said, you can look at the code in GitHub to see how we are using this for Connection and Battery.

This is how I solve problems like your.
1) Create and associate a JavascriptInterface to your WebView. A JavascriptInterface is simply a class inside which you can declare some Java method you want to use from JS.
public class JSInterface() {
private final CountDownLatch latch = new CountDownLatch(1);
public void waitForProceed() {
try {
latch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public void canProceed() {
latch.countDown();
}
}
2) In your AsyncTask, at the end of onPostExecute() method, you have to call the canProceed() method to notify to JSInterface that it can exit from waitForProceed() method.
public class MyAsyncTask extends AsyncTask<.......> {
private JSInterface jsi;
... // other class property
public MyAsyncTask(JSInterface jsi) {
...
//do what you want with other class property
this.jsi = jsi;
}
#Override
public ... doInBackground(...) {
...
//do something
}
#Override
public void onPostExecute(...) {
...
//do something
jsi.canProceed();
}
}
3) In your Activity you have to associate the JSInterface object to your WebView:
WebView mWebView;
...
mWebView.getSettings().setJavaScriptEnabled(true);
mWebView.addJavascriptInterface(new JSInterface(), "JSIface");
4) Finally, in JS, you can call AsyncTask (I don't know how you call it, but I guess you use somthing like a JSInterface) and after call waitForProceed() method:
startAsyncTask(); //somehow
JSIface.waitForProceed();
I hope it solves your problem ;)

Here is a detailed example:
Lets create some interface that should be called when AsyncTask will finish the stuff, a.e when onPostExecute called.
In my case we fetch some JSONArray data
MyTaskListenerItf.java
public interface GroupTaskListenerItf {
public void onTaskDone(JSONArray groupArray);
}
The AsyncTask template of looks like:
MyBuildTask.java
public class MyBuildTask extends AsyncTask<Void, Void, SomeData>{
private MyTaskListenerItf mTl = null;
public MyBuildTask(Context context, MyTaskListenerItf tl) {
super();
this.mContext = context;
this.mTl = tl;
}
#Override
protected SomeData doInBackground(Void... params) {
/* ... */
}
#Override
protected void onPostExecute(WmTransferItem transferItem) {
// ...
if(this.mTl != null){
JSONArray data = new JSONArray("");
this.mTl.onTaskDone(data);
}
// ..
}
}
So now our CordovaPlugin class should look like:
MyCordovaPlugin.java
public class MyCordovaPlugin extends CordovaPlugin implements GroupTaskListenerItf {
// we need this callback when Task will finish
private CallbackContext mMyCallbackContext = null;
#Override
public boolean execute(String action, JSONArray args,CallbackContext callbackContext) throws JSONException {
if("runMe".equals(action)){
final GroupTaskListenerItf gt = this;
mMyCallbackContext = callbackContext;
// pass our 'GroupTaskListenerItf' interface to async class
MyBuildTask task = new MyBuildTask(cordova.getActivity(), gt);
task.execute();
PluginResult pluginResult = new PluginResult(PluginResult.Status.NO_RESULT);
pluginResult.setKeepCallback(true);
callbackContext.sendPluginResult(pluginResult);
}
else{
this.cordova.getThreadPool().execute( new Runnable() {
public void run() {
// BTW, here you might run something else out of UI Thread
}
});
}
}
/* ... */
#Override
public void onTaskDone(JSONArray data) {
if (this.mGroupCallbackContext != null) {
PluginResult result = new PluginResult(PluginResult.Status.OK, data);
result.setKeepCallback(false);
this.mMyCallbackContext.sendPluginResult(result);
}
}
That's all.
Hope it will help to someone.