Access to WebView from another function in MainActivity class

You're trying to use view before it has been initialized. You need to wait until after view = (WebView) findViewById(R.id.webView); has been called in order to initialize onServerReceive.

EDIT: Looking at this some more what's more likely happening is that you're using your instance of onServerRecieve before view is initialized in onCreate().

@Overridepublic void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    ...    view = (WebView) findViewById(R.id.webView);    onServerRecieve = createListener()    view.getSettings().setJavaScriptEnabled(true);    ...    view.loadUrl("file:///android_asset/loading.html");}...@JavascriptInterfacepublic void websocket_start(){    try {        mSocket = IO.socket("http://some web com:8888");        mSocket.on("connect", onConnect);        mSocket.on("server_receive", onServerReceive);        mSocket.connect();    } catch (URISyntaxException e) {}}private Emitter.Listener createListener() {    return new Emitter.Listener() {    @Override    public void call(final Object... args) {        runOnUiThread(new Runnable() {            @Override            public void run() {                final String argsStr = TextUtils.join(",", args);                view.loadUrl("javascript:receive('" + argsStr + "')");            }        });    }};}public Emitter.Listener onServerReceive;}

Finally found the answer and the problem

I had this

view.addJavascriptInterface(new MainActivity(), "access_android");

and in web js I accessed android with this "access_android.websocket_emit()"

and i think because of "new MainActivity()" it was creating a new class where "view" wasn't defined. so I replaced "new MainActivity()" with "this"

view.addJavascriptInterface(this, "access_android");

now all works fine ! thanks good bye