EvaluateJavascript or LoadUrl is not being executed at all in Xamarin

Question

I'm trying to share some data from an Activity to JavaScript, but all my results have failed, this is my current code:

C#

var webView = FindViewById<WebView>(Resource.Id.webView);

webView.SetWebChromeClient(new WebChromeClient());

webView.Settings.JavaScriptCanOpenWindowsAutomatically = true;
webView.Settings.JavaScriptEnabled = true;
string script = string.Format("javascript:UpdateData('{0}','{1}','{2}','{3}','{4}','{5}','{6}','{7}','{8}');", "1", "2", "3", "4", "5", "6", "7", "8", "9");

webView.LoadUrl("file:///android_asset/index.html");

if (Build.VERSION.SdkInt >= BuildVersionCodes.Kitkat)
{
    webView.EvaluateJavascript(script, null);
}
else
{
    webView.LoadUrl(script);
}

JavaScript inside of index.html (I tried to add the code in the head and in the end of the body too):

<script type="text/javascript">
    function UpdateData(arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9) {
        alert("Hi");
    }
</script>

AndroidManifest.xml

<?xml version="1.0" encoding"utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="Test.Test" android:versionCode="1" android:versionName="1.0">
    <uses-sdk android:minSdkVersion="19" />
    <application android:label="Test"></application>
  <uses-permission android:name="android.permission.INTERNET" />
</manifest>

Honestly, I don't know what I'm doing wrong because nothing happens, the basic web page is rendered perfectly, but the JavaScript is not triggered. Has anyone experienced this before?

These are my configurations if they can be useful:

Martin Zikmund · Accepted Answer · 2016-11-23 08:11:10Z

5

I think the problem is that you are trying to evaluate the script immediately after you load the URL. After you call webView.LoadUrl(...), the WebView needs some time to fully load the page including the contained <script>.

What you need is to create a class derived from WebViewClient and override the OnPageFinished method.

public class JavaScriptWebViewClient : WebViewClient
{
    public override void OnPageFinished(WebView view, string url)
    {
        base.OnPageFinished(view, url);

        string script = string.Format("javascript:UpdateData('{0}','{1}','{2}','{3}','{4}','{5}','{6}','{7}','{8}');", "1", "2", "3", "4", "5", "6", "7", "8", "9");

        if (Build.VERSION.SdkInt >= BuildVersionCodes.Kitkat)
        {
            view.EvaluateJavascript(script, null);
        }
        else
        {
            view.LoadUrl(script);
        }
    }
}

And your original code would then need to set the web client:

var webView = FindViewById<WebView>(Resource.Id.webView);
webView.SetWebChromeClient(new WebChromeClient());
webView.Settings.JavaScriptCanOpenWindowsAutomatically = true;
webView.Settings.JavaScriptEnabled = true;

//set the custom web client
webView.SetWebViewClient(new JavaScriptWebViewClient());

webView.LoadUrl("file:///android_asset/index.html");

answered Nov 23, 2016 at 8:11

Martin Zikmund

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3 Comments

Federico Navarrete Over a year ago

The best solution ever! Thanks!

Nasser Mansouri Over a year ago

very usefull ,thanks but i think there is some error in your answer, for example : if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT)...

Martin Zikmund Over a year ago

Oh, it should not be, the question was for Xamarin.Android, which is C# version of Android API, which has different naming conventions than Java :-)

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