web developer padawan: December 2016

30 December 2016

Improving on SimpleDateFormat

I'm a big fan of SimpleDateFormat, but it suffers from one critical problem. Your date format is forced on the user. I've learnt the hard way (as have most developers) that American's have their own date format (mm/dd/yyyy), us Brits have our own format (dd/mm/yy) and of course there are many other countries that also have different ideas.

Using SimpleDateFormat means you pick a format and the user has to like it. In some cases this could even be very frustrating for the user. You could of course allow them to pick their own format, but that's a lot of work.

My point here is Android has a little used method of doing this hard work for you and it utilizes the user's locale as set in the phone settings, to calculate this format. That is java.text.DateFormat.
So if the user has English American locale, then DateFormat will use that, if it has en-UK then that's the format it'll use. Magic!


import java.text.DateFormat;
DateFormat dateTimeFormat;


dateTimeFormat = DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.SHORT, Locale.getDefault());


Date date = new Date();
dateTimeFormat.format(date);

Next time you're displaying a date or a time, why not try using DateFormat instead of forcing your format on the user?

22 December 2016

Inject Javascript into Android WebView

Here's an interesting one I stumbled across the other day. The ability to "inject" some javascript into a webview and override the existing javascript for a webpage.

Let's say you want to override an existing javascript function, maybe one that's broken or you just want to change functionality. This is possible using onPageFinished.

Now I'm not going to say you *should* do this, nor will I say it is recommended or a good idea. I'm just pointing out that it's possible and saying it's mildly interesting.
Obviously there are warnings that go with enabling javscript on your webview and you should take heed of them over my example here.

Here's my HTML that I will load in a webview. For this example I've loaded it locally from my assets folder. I see no reason why this wouldn't work on a remote page.


<html>
    <head>
        <title>hello</title>
        <script>
            function myFunction() {
                document.getElementById("demo").innerHTML = "Gonzo was here";
            }
        </script>
    </head>
    <body>
        <p>
            <button name="Sumit" label="Submit" value="Submit" id="Submit" onclick="myFunction()">Submit</button>

            <br /><br />
            <div id="demo">Hello</div>
        </p>
    </body>
</html>

Let's try and change that javascript function to do something else:


final WebView webView = (WebView) findViewById(R.id.webView);

webView.setWebViewClient(new WebViewClient() {
    @Override
    public void onPageFinished(WebView view, String url) {
        super.onPageFinished(view, url);
        webView.loadUrl("javascript:function myFunction(){document.getElementById(\"demo\").innerHTML = \"Paragraph changed.\";}");
    }
});

WebSettings webSettings = webView.getSettings();
webSettings.setJavaScriptEnabled(true);
webView.loadUrl("file:///android_asset/test.htm");

As you can see we've injected a custom function that overrides the results with a different output. Interesting huh?