I really like Android's EditText

In the last couple of days I enjoyed doing a little bit coding for Android at home. With a J2ME background I was really amazed by the richness of the Android APIs. You have a lot of the Java Standard Edition APIs plus a lot of useful and well thought out APIs for UI and phone related stuff.

I quickly realized that a lot of functionality I thought I have to implement myself is already there. For example I really like the preferences API. On J2ME I had to implement everything myself. Starting from the preferences UI to the preference store.

Also surprising for me was how rich the widgets really are. Let's take the EditText widget. It not only looks really good when rendered on the screen it also has a lot of functionality you can easily use.

For my first application I have a form to enter geocoordinates. They are represented as text like "50:24,123".

After the basics worked I wanted to make the UI a little bit more user friendly by helping the user to enter only valid coordinates.

First I wanted to limit the usable characters to "0123456789:,.-". And it turned out to be quite simple:

NumberKeyListener keyListener = new NumberKeyListener() {

        public int getInputType() {
        return InputType.TYPE_CLASS_NUMBER;

        protected char[] getAcceptedChars() {
        return new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.', ':', '-', ',' };


But this still doesn't prevent someone from entering something like "1:1:1:1" which is obviously not valid. So I introduced an input filter:

    InputFilter[] filters = new InputFilter[1];

    filters[0] = new InputFilter() {

        public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
        if (end > start) {
            String destTxt = dest.toString();
            String resultingTxt = destTxt.substring(0, dstart) + source.subSequence(start, end) + destTxt.substring(dend);

            if (!resultingTxt.matches("[0123456789]*[\\:]?[0123456789]*[,.]?[0123456789]*")) {

            if (source instanceof Spanned) {
                SpannableString sp = new SpannableString("");
                return sp;
            } else {
                return "";


        return null;



(Please note that this is just an example and the code isn't production quality.)

That was easy and a lot better. Unfortunately you can still enter invalid coordinates like "999:99.123".

First I thought of getting all the magic into the regexp but first I don't like regexp-magic so much and second I wanted to see how I can give the user some feedback about the validity of the entered data.

I decided to implement a TextWatcher and validate the data in "afterTextChanged".

There I just tried to parse the coordinate and in case of an error I wanted to inform the user. My first approach was to use a Toast but it turned out that EditText already has everything I needed.

The code looked like this:

    } else {
        lonEditText.setError("Coordinate is invalid.");

This is not the actual source but it shows what I wanted to show: Use setError to indicate a problem with the text contained in that EditText.

When the invalid field has focus the error is displayed. If it's not focused there is an icon showing that something is wrong with the content of this field.

That was easy and it's more than I had expected. Thanks Android!


Fragmentation is inevitable

Many J2ME developers are complaining about device fragmentation. And I agree that it's one of the hardest challenges when developing portable MIDlets.

Recently similar things are said about Android. (see http://androidandme.com/2009/11/news/what-does-android-fragmentation-look-like/ )

And even on the iPhone there are similar problems. And I think that those problems are inevitable when you don't want to stick to old and outdated technology.

But why does fragmentation occur? What are the reasons for it?

  • Different software / hardware vendors. Even if the specs are very similar the details of an implementation can make the difference. This affects J2ME a lot. Luckily Android devices are more similar in terms of OS implementation but the hardware varies. The iPhone is the clear winner here. There's only one vendor. (Well this is in my opintion one of the few things that are good about having one vendor only.)
  • Software evolution.  (i.e. new versions) Software normally gets better and better with each revision and usually users want to use the latest features. But not all users can or want to update their devices. So you have to deal with multiple versions.
  • Hardware evolution. New devices have higher screen resolutions, more memory, more sensors etc.  If you want to make use of those new capabilities and don't want to break compatability with less powerful devices you have to write smart applications.

In the end device fragmentation is the consequence of device evolution. And we have to live with it because it won't go away.

Even controlled platforms like the iPhone are affected by this. Not as much as others but even iPhone developers have to deal with it. The next big change to that platform might be the introduction of new HD models with higher screen resolutions. We will see how those developers can deal with it. On other platforms people are already used to different screen sizes but I guess only few iPhone developers today think about screen size.