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how to delete an element in xamarin forms webview

i want to delete an element in Xamarin.forms WebView when it's loading but it return null and app crash . how can i do this?
i tried to check if an element exist but dont have any success.
this is my code
protected void OnNavigating(object sender, WebNavigatingEventArgs args)
{
Webview.Eval("const elements = document.getElementsByClassName(\"footer-section\"); while (elements.length > 0) elements[0].remove();");
}
please help me. thanks

You are getting a null exception because the WebView is not loaded when you try to execute Javascript.
In order to prevent this, you can subscribe to OnNavigated Event:
WebView.Navigated Event
Event that is raised after navigation completes.
So, here is a sample:
public YourWebViewPage()
{
InitializeComponent ();
Webview.Navigated += WebViewNavigated;
}
private void WebViewNavigated(object sender, WebNavigatedEventArgs e)
{
Webview.Eval("const elements = document.getElementsByClassName(\"footer-section\"); while (elements.length > 0) elements[0].remove();");
}

You can try to override function onPageCommitVisible
The Android documentation says:
This callback can be used to determine the point at which it is safe
to make a recycled WebView visible, ensuring that no stale content is
shown. It is called at the earliest point at which it can be
guaranteed that WebView#onDraw will no longer draw any content from
previous navigations. The next draw will display either the
WebView#setBackgroundColor of the WebView, or some of the contents of
the newly loaded page.
This method is called when the body of the HTTP response has started
loading, is reflected in the DOM, and will be visible in subsequent
draws. This callback occurs early in the document loading process, and
as such you should expect that linked resources (for example, CSS and
images) may not be available.
You can try the following code:
public override void OnPageCommitVisible(WebView view, string url)
{
string _javascript = "const elements =
document.getElementsByClassName('footer-section'); for(i=0;i<elements.length;i++) {
if(elements[i] != null){ elements[i].parentNode.removeChild(elements[i]); }}";
view.EvaluateJavascript(_javascript, null);
base.OnPageCommitVisible(view, url);
}

Trying to parse JSON of a web page before it's loaded in a WebView

I need to parse JSON content out of every page in my WebView, before it is shown to the user.
In order to do so, I need to parse the JSON element and only then I’m able to use the shouldOverrideUrlLoading method. I can’t use it before I’ve parsed the JSON object because I rely on that element as part of my implementation of that method.
I have created a variable called jsonParsed to indicate whether I have all needed information out of the JSON object.
At first, it is initialized to be false.
When I get a response from the server I know the object was parsed so I change the variable to be true in the onLoaded method, and then the code is ready to get the information and check it.
This is the wanted process:
Opening new page by the user
Entering automatically to shouldOverrideUrlLoading and then to the if statement(JSON wasn't parsed yet)
Getting the JSON response in OnResponse
Going back to shouldOverrideUrlLoading and entering the else statement (JSON is parsed)
As you can see, each process should go through both if and else statements, the if before the JSON was parsed, and the else after it was parsed.
The problem:
shouldOverrideUrlLoading is reached every step 1, but each time it goes into a different statement. The first time goes into the if (steps 2+3), and the next one goes into the else (step 4) and this process repeats itself...
I think the this line webView.loadUrl(loadingURL); doesn't call shouldOverrideUrlLoading for some reason.
Here is my code snippet:
#Override
public void onPageStarted(WebView view, String url, Bitmap favicon)
{
super.onPageStarted(view, url, favicon);
mProgressDialog.show();
}
#Override
public boolean shouldOverrideUrlLoading(WebView wView, String url){
loadingURL=url;
if (!jsonParsed){
/** JSON object is not parsed
* Some code for adding request
to requestQueue and than loading new url in onResponse method... */
}
else {
/** JSON object is parsed, starting checking process
* I need to check this URL and decide whether or not to override it*/
jsonParsed=false;
Root root = new Gson().fromJson(jsonResponse, Root.class);
for (Page page : root.query.pages.values()) {
firstParagraph=page.extract; //Parsing process, works fine
}
if (firstParagraph!=null) {
//If the webView isn't Wikipedia's article, it will be null
if (firstParagraph.contains(allowedContent)) {
//Passing URL to view
return true;
}
}
return false; //The URL leads to unallowed content
}
}
#Override
public void onPageFinished(WebView view, String url) {
CloseBlocksAndDisableEdit(view);
mProgressDialog.dismiss();
}
private final Response.Listener<String> onLoaded = new Response.Listener<String>() {
#Override
public void onResponse(String response) {
jsonResponse=response; //Getting response
jsonParsed=true; //Object was examined
webView.loadUrl(loadingURL);
}
};
What can be the cause of this problem?
If it's not possible in this way, I'd like to know which way is better...

I have found this answer:
https://stackoverflow.com/a/6739042/7483311
It is written in this answer:
After some research I conclude that despite what most of the tutorials
out there say, shouldOverrideUrlLoading() does not get called when:
You load a URL like:
loadUrl("http://www.google.com");
The browser redirects the user automatically via an HTTP Redirect.
This probably makes my code impposible.
In this line: webView.loadUrl(loadingURL);, I'm making an https request that was not made by the user in the WebView, and that's why it doesn't call shouldoverrideurlloading.

WebView not working consistently

Edit: Strangely works when duplicating the loadUrl() line
I'm working with WebViews to gather data from a webpage. Sometimes, the webview just does nothing. I tried many proposes, but actually, none of them works....
Strange: webview.loadUrl("url...") doesn't work, but as soon as I call it twice, it works...
checkLogin()
void checkLogin(final Context context) {
Log.d("checkLogin()", "Begin of checkLogin()");
WebView webview = returnNewWebView(context, false);
webview.setWebViewClient(new WebViewClient(){
#Override
public void onPageFinished(WebView view, String url) {
Log.d("url", url);
// GOOGLE.COM ACTUALLY WORKS!
if(url.equals("https://www.google.com/"))
return;
Log.d("checkLogin()", "Loading of checkpage finished");
if(url.contains("loginto.php")) {
Log.d("checkLogin()", "User is logged out");
OnLoginCheckListener.onLoginCheckLoggedOut();
} else {
Log.d("checkLogin()", "User is logged in");
OnLoginCheckListener.onLoginCheckLoggedIn();
}
}
});
String id = sharedPref.getString("id", null);
String transid = sharedPref.getString("transid", null);
if(TextUtils.isEmpty("id") || TextUtils.isEmpty("transid")) {
Log.d("checkLogin()", "No login found, starting LoginActivity()");
Intent myIntent = new Intent(context, LoginActivity.class);
context.startActivity(myIntent);
} else {
Log.d("checkLogin()", "Probably logged in, checking by loading startpage");
webview.loadUrl("https://www.google.com");
// google actually works -.-
webview.loadUrl("https://my.login-page.com/index.php?pageid=1&id=" + id + "&transid=" + transid);
}
}
returnNewWebView()
private WebView returnNewWebView(Context context, Boolean JSInterface) {
// Prepare a webview
WebView WebView = new WebView(context);
if(JSInterface) {
WebView.getSettings().setJavaScriptEnabled(true);
WebView.addJavascriptInterface(new JavaScriptInterface(), "AndroidInterface");
}
// We don't need images for data scraping...
WebView.getSettings().setLoadsImagesAutomatically(false);
WebView.getSettings().setCacheMode(WebSettings.LOAD_NO_CACHE);
// Allow cookies
CookieManager.getInstance().acceptCookie();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
CookieManager.getInstance().acceptThirdPartyCookies(WebView);
}
// Prevent webview not loading
// or try it...
WebView.clearCache(true);
WebView.destroyDrawingCache();
return WebView;
}
As you see, I already tried some stuff in order to prevent it but still, it doesn't work. In that cases, as soon I'm going to put the loadUrl() / postUrl()twice, it works.
What can I do that it works in every single case?
I would appreciate any tip!
Thank you very much in advance
logcat (non-filtered)
I actually see this message then..
03-09 07:36:19.061 4111-24251/? E/ctxmgr: [ProducerActiveIntervalImpl]closeActiveInterval: Error: ongoing, trying to close
and this one:
03-09 07:36:28.864 29862-3249/? E/accs.GcmPush: initializeApp occur error!
java.lang.IllegalStateException: FirebaseApp name [DEFAULT] already exists!
at iv.a(Unknown Source)
at com.google.firebase.FirebaseApp.a(Unknown Source)
at com.google.firebase.FirebaseApp.a(Unknown Source)
at org.android.agoo.gcm.GcmRegister$1.run(GcmRegister.java:32)
and this one too:
E/libEGL: validate_display:99 error 3008 (EGL_BAD_DISPLAY)
But I can't tell you if they are fired by the app....

I have gone through the full code for so long and pointed out this :
You are using this -
webview.loadUrl("https://www.google.com");
// google actually works -.-
webview.loadUrl("https://my.login-page.com/index.php?pageid=1&id=" + id + "&transid=" + transid);
in your checkLogin() method which is simply wrong as because one webview can not display the two urls at same time (as you mentioned it you want to achieve that).
Now according to your code the loading of the first url is overridden by the second url.
In order to achieve the loading of two urls in same webview try to implement this using :
Threads or some sessionTimeout methods.
OR
You can achieve this by using okhttp package.
Hope this helps!

onPageFinished is called when the webpage finished loading, but not after all the javascript on the page finished running. Depending on what the page is doing and what you are trying to achieve, it might be that your code is sometimes being executed before some essential javascript is executed on that page.
It's not a pretty solution but try adding some delay (like a Handler's postDelayed() or SystemClock.sleep() - but never on the UI thread!) to your code to see if that is indeed your problem.

How to establish communication between webview and html page in worklight?

I'm working on making a browser as a hybrid app using worklight framework for Android. I implemented my address bar as an input element which received the user input and pass the arguments to the webview to load the page.
However, I cannot figure out how to do the reverse: whenever the user click on a link in webview, I want the address bar to change to the new location.

Are you implementing a native page that is opened? If so, take a look at ChildBrowser, that basically does the same thing. It has a TextView being used as an address bar. You may decide to use it, or get the bits and pieces you want out of it. Regardless, I would image what you want to do something like this. By overriding the onLoadResource in the WebViewClient, you should be able to grab the url and change your TextBox.
In response to the comment below: inside your environment's main js file in the wlEnvInit() function:
function wlEnvInit(){
wlCommonInit();
// Environment initialization code goes here
document.onclick=manageLinks;
}
Then in this function get the url and set the text of your input element:
function manageLinks(event) {
var link = event.target;
//go up the family tree until we find the A tag
while (link && link.tagName != 'A') {
link = link.parentNode;
}
if (link) {
var url = link.href;
console.log("url = " + url);
//You can decide if you want to separate external or
//internal links, depending on your application
var linkIsExternal = ((url.indexOf('http://') == 0) || (url.indexOf('https://') == 0));
if (linkIsExternal) {
myInput.setText(url);
return false;
}
}
return true;
}
Inside of your WebView, inside the plugin, intercept the URL like this:
webview.setWebViewClient(new WebViewClient() {
#Override
public void onPageFinished(WebView view, String url) {
//use this area to set your input. Depending on how you
//implemented your plugin, you may need to return this value
//back to your main activity
Toast.makeText(cordova.getActivity(), "Loading: " + url, Toast.LENGTH_LONG).show();
}
});

Have you try to get the url from the href of and assign to the input variable and do the get/post? I know that it is possible in SDK i figure it dont will be harder in a framework. You can store the hiperlinks in a array with a parser or something similar.
example pseudocode:
When_hiperlink_clicked: //could be like a listener (search about it)
url = hiperlink.getURL("myHiperlink");
myinput.setText(url);
execute_input_bar_action();
Is difficult to figure out without code or something more, sorry.

Android webview onReceivedError display custom error page and reload previous url onResume

We suppose that a url is already loaded (Let's call it the original url).
webView.setWebViewClient(new WebViewClient() {
#Override
public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
webView.loadUrl("file:///android_asset/missing.html");
}
});
I have created my own error page to prevent the "web page not available message" to appear.
The app must reload the webview every time it is resumed. So i have the following lines of code:
#Override
protected void onResume() {
super.onResume();
webView.reload();
}
The problem here is that when the error page is loaded (for example when the user is not connected to the internet), and then a connection is available again and the user resumes the app, the original url is not loaded (which seems logic, the current now is missing.html). But is this a nice approach? Any suggestions for the problem?
There is also a refresh button if the user wants to reload the content. Same issue here.

You should load the wanted url instead of using webView.reload(), like this:
webView.loadUrl("http://yoururl");
or go back to previous page with:
webView.loadUrl("javascript:history.go(-1)");

I'd examine internet connectivity in onResume() like suggested on http://developer.android.com/training/basics/network-ops/managing.html
public static boolean isOnline() {
ConnectivityManager connMgr = (ConnectivityManager) App.instans.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
return (networkInfo != null && networkInfo.isConnected());
}
public void onResume() {

It's not just the mobile connection that can drop but also the page can become unavailable and as you rightly say using webview.loadUrl("someerrorpage.html") will create fake history and cause problems if the user tries to refresh or press back.
My solution was to replace the contents of the default error page with my own custom one e.g.
webView.evaluateJavascript("javascript:document.open();document.write('your custom error html');document.close();", null);