Indeed, quite simple, but still.

Limiting character amount

The first goal was to limit the amount of characters someone can type in an EditText. Well, this sounds easy and it is. You can set a filter, like so:

editText.setFilters(new InputFilter[]{
         new InputFilter.LengthFilter(MAX_SIZE)
});

Limiting to a certain value

Now to implement this for the setting that stops you from asking for a million pictures to be downloaded.

To be clearer: I have a preference that lets you set the amount of pictures you can download. You should be able to write only numbers* here.. I’ve done this, more or less inelegantly, with the “android:digit” attribute in the xml:

<EditTextPreference
       android:title="Max Amount"
       android:summary="The more, the heavier. Default = 12"
       android:key="viewMax"
       android:defaultValue="12"
       android:digits="0123456789"/>

* no, we’re not entering the amount in HEX.

This works OK, but you can type in a lot of 9′s if you want. That’s no good.

Now to add another LengthFilter is only applicable for numbers  up to (10^y)-1, e.g. up to 999: a LengthFilter(3) will of course limit you to 3 characters, not to an int of max 3.

I have not found a filter for the maximum value, as the standard InputFilter gives us “ALLCAPS” and the previously used LengthFilter. I think the cleanest method might be to write an InputFilter, but it’s rather easy to fix without one, using an OnSharedPreferenceChangeListener.

Simple summary of how to limit an edittext to a certain value

We can add a lot of Listeners, that trigger on a lot of different moments, this is just an example. The moment of warning might be a bit late (after having set the value), but as a proof-of-concept:

Implement OnSharedPreferenceChangeListener

Whenever you’ve changed the preference, trigger a function to check if everything is sane. The activity implements OnSharedPreferenceChangeListener, so you can do this:

getPreferenceScreen().getSharedPreferences()
              .registerOnSharedPreferenceChangeListener(this);

The Listener

Add the listener. It will check for the set value, and correct it if it’s not sane.

public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
		String key) {
  if ("yourPrefName".equals(key)) {
    String valueString = sharedPreferences.getString(key, "");
    int value = Integer.parseInt(valueString);
    if(value > MAX_VALUE){
	EditTextPreference p = (EditTextPreference) findPreference(key);
	p.setText(""+MAX_VALUE);
	Toast t = Toast.makeText(this,"Maximum amount limited to "+MAX_VALUE, Toast.LENGTH_SHORT);
	t.show();
    }else if(value < MIN_VALUE){
	EditTextPreference p = (EditTextPreference) findPreference(key);
	p.setText(""+MIN_VALUE);
	Toast t = Toast.makeText(this,"Minimum amount limited to "+MIN_VALUE, Toast.LENGTH_SHORT);
	t.show();
    }
}

This means that you CAN enter numbers that are too high or too low, but at least you’ll get a message saying you’ve failed, and the preference will remain something sane.

Bonus: a filter on an EditTextPreference

Now for a quick bonus. I was annoyed at first why you cannot simple add a filter to your EditTextPreference like you would with an EditText

yourEditTextPreference.setFilters(yourFilters);

This is because the input you’re getting for a preference actually is an EditText, and you’ve got to find it. Short story even shorter: get the EditText from the EditTextPreference. Duh :)

yourEditTextPreference.getEditText().setFilters(yourFilters);

Now I’ll see how fun it is to write a real filter. Why not?

Time to catch up on some of the android blogposts! Lets start with a simple one: this annoying bug stops you from opening the very usefull Hierarchy-viewer.

“Failed to get the adb version: Cannot run program “adb.exe”: CreateProcess error=2, The system cannot find the file specified”

There seem to be several issues here, ranging from installing all sorts of new stuff to reinstalling the SDK, but there’s one sollution that has helpt me on 2 different (windows) machines: adding the new location of the “adb.exe” to your environment path.

Step 1: locate adb.exe. It wil probably be in the platform-tools dir (that’s new I guess)

Step 2: add the location to your PATH. In windows 7:

• Rightclick on “my computer”
• Advanced system settings (on the left)
• Button “Environment Variables”
• Select “PATH” and press “Edit…”
• Add your path, e.g. add in the end: “;c:\android\sdk\platform-tools
• press all OK buttons.

Win!

When you have HTML and you want to show it to your users, one of the possibilities is using a WebView. Check the WebView tutorial for more info. You can also use a TextView, but the HTML has to be changed for that. You could use linkify for this. This should be enough, but when you also want (for instance) bold and italic to work, we have to do some more trickery. The first iteration we used was this:

//description is a TextView
description.setText(Html.fromHtml(desc));
description.setMovementMethod(LinkMovementMethod.getInstance());

This works amazingly well, except for this ‘minor’ detail: full links are working perfectly, but a link like this does a force close:

<a href="/dr">Link with relative path</a>

The TextView is not a browser, so it doesn’t even know what protocol we are using, let alone what domain or path we’re supposed to be in. This will result in a force close, with a log that looks like this:

ActivityNotFoundException: No Activity found to handle Intent { act=android.intent.action.View data=/dr}

The intent expects something like “http://” or “mailto:” I presume, but if it gets “/dr”, there is no activity to handle the link.

Elegance aside, a simple solution is to make an absolute link if you know the correct data. This is a quick and dirty solution, but let’s share it anyway because a lot of solutions we found were specifically for linkify, not for complete “fromhtml” purposes.

/**
 * Removes relative a hrefs
 * @param spantext (from Html.fromhtml())
 * @return spanned with fixed links
 */
public Spanned correctLinkPaths (Spanned spantext) {
  Object[] spans = spantext.getSpans(0, spantext.length(), Object.class);
  for (Object span : spans) {
    int start = spantext.getSpanStart(span);
    int end = spantext.getSpanEnd(span);
    int flags = spantext.getSpanFlags(span);
    if (span instanceof URLSpan) {
      URLSpan urlSpan = (URLSpan) span;
      if (!urlSpan.getURL().startsWith("http")) {
        if (urlSpan.getURL().startsWith("/")) {
          urlSpan = new URLSpan("http://domain+path" + urlSpan.getURL());
        } else {
          urlSpan = new URLSpan("http://domain+path/" + urlSpan.getURL());
        }
      }
      ((Spannable) spantext).removeSpan(span);
      ((Spannable) spantext).setSpan(urlSpan, start, end, flags);
    }
  }
  return spantext;
}

We traverse the objects in the Spanned. If we find a URLSpan we copy the span and fix that one. Then we remove the old span, and insert the new one. The copy move might not be necessary, but as it doesn’t bother us at the moment I’ll leave it like this. This has taken up quite enough time, thankyouverymuch. If you want to do something extra, and instead of opening a browser do your own onClick magic, you can take a look at this anddev forumthread.

Finally, our assign has to look like this obviously:

//description is still a TextView
description.setText(correctLinkPaths(Html.fromHtml(desc)));
description.setMovementMethod(LinkMovementMethod.getInstance());

Another interesting link is this bugreport on code.google.com. I’d say that your browser shouldn’t know where to point itself, but apparently the project members don’t agree.

It seems that a WebView element in Android reserves some space for a vertical scrollbar by default. This shows up as a small, vertical strip of white space on the right, which is not padding or margin but some space reserved for a scrollbar.

To get rid of this you have to set the scrollbar style to display the scrollbars inside the content area. This can be done with the following code:

webview.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);

This morning I woke up to this little message:

Error generating final archive: Debug certificate expired on 8/23/10 8:45 AM!    AndroBlip.coffee        Unknown    Android Packaging Problem

Well, that was annoying. According to google this is expected after your debug key is a year old. I have no clue why this is; it doesn’t seem to have any purpose, but luckily they do find us a solution:

To fix this problem, simply delete the debug.keystore file. The default storage location for AVDs is in ~/.android/avd on OS X and Linux, in C:\Documents and Settings\\.android\ on Windows XP, and in C:\Users\\.android\ on Windows Vista.

The next time you build, the build tools will regenerate a new keystore and debug key

This also seems to happen if you’re on a non-gregorian locale, but that’s not the case for me. Check out that google link for that one.

Minor note: running the program on the same virtual machine, gives you trouble with a new signing/debug key:

installation failed due to different application signatures.
You must perform a full uninstall of the application. WARNING: This will remove the application data!
Please execute ‘adb uninstall com.huiges.AndroBlip’ in a shell.
Launch canceled!

Just uninstalling the application in the virtual machine works fine.
It does however mean that if you work with a lot of test-data in your app, you’ll have to find a way to keep that around when uninstalling your app. As far as I know this is unavoidable when your key expires. This site comes up with a solution: create your own key with a much larger expiration date:

keytool -genkey -keypass android -keystore debug.keystore -alias androiddebugkey -storepass android -validity 10000 -dname "CN=Android Debug,O=Android,C=US"