Develop Reference

How can I display algebraic expressions as a String?

How can I display some calculus with variables and indices as a String in android? Or even just a simple radical sign over some numbers?

TextView in Android supports UTF-8, so you can use non-typical characters like: ≠, ÷, =, ∑, ∈, etc.
Full list here: http://en.wikipedia.org/wiki/List_of_mathematical_symbols

You can use unicodes
You can get list of unicodes from this link
for example
If you want to use ∑ use
android:text="/u2211"
attribute in xml
OR
textView.setText("/u2211")
You can also use in HTML like
.setText(Html.fromHtml("X<sup>2</sup>")); for X^2

Android Charsequence - replacing text

Due to HTML usage within a string resource, I can't convert this to string from a charsequence (I will lose the formatting otherwise).
<string name="exponent_key">x<sup><small>y</small></sup>/string>
After using getString() I want to replace the 'y' with 'other stuff' but how do you do that? It seems like a simple question but for some reason I can't find anything about it.
Edit: Now that I think about it, can I convert the charsequence to a string that contains the HTML code, and then convert it back to a charsequence later?
Edit: Forgot to mention that the string gets set to a button title, and then retrieved (where it is then used).

There is. Create a function where, as a parameter, you take a string that needs to be formatted. And in function, you just take it through itterator, and after that Html.fromHtml()

in your string.xml
<string name="exponent_key">x<sup><small>%1$d</small></sup></string>
in your code
textView.setText(getString(R.string.exponent_key,2))

Let's break down your question in multiple steps:
Replacing the y with "other stuff" can be done like this:
String.format("%1$", "otherStuff");
If you use getString(), you can do the same thing like that:
<string name="exponent_key">%1$</string>
---
String string = getString(R.string.exponent_key, "otherStuff");
For more than one element, do this way:
you can do that like this:
<string name="string_name">%1$ : %2$</string>
---
getString(R.string.string_name, new String[]{"hello", "world"});
In XML you cannot nest HTML code, since HTML is another type of XML and the parser messes up and cannot recognize what tags are for Android and what are for HTML. But.. there's a trick. You can do that in this way:
<string name="exponent_key"><![CDATA[x<sup><small>%1$</small>/sup>]]></string>
So, with the string above in your XML, just use and you're fine:
getString(R.string.exponent_key, "otherStuff");
Note: if you need to show the HTML in a TextView, just use Html.fromHtml:
textView.setText(Html.fromHtml(getString(R.string.exponent_key, "otherStuff")));

Consider the effect you want to achieve.
you can do like this.
SpannableString ss = new SpannableString("2");
// set superscript
ss.setSpan(new SuperscriptSpan(),0,ss.length(),Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
// set font size
ss.setSpan(new AbsoluteSizeSpan(12,true),0,ss.length(),Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
tv.append(ss);

Android: How store url in string.xml resource file?

I'm trying to store a fully qualified url, with also query params:
www.miosito.net?prova&reg=bis
but it's causing a problem because &reg is similar to ® entity and android tell me that and html entity is not well written.
I need this because every locale uses a fully different set of url query param.
I tried with [[CDATA[.. ]] but this syntax disliked by xml parser.

The problem is not with &req but with & itself. For XML/HTML you would have to use & entity (or &), but for URLs you should rather URL-encode (see docs) strings, and in that case said & should be replaced with %26. So your final string should look like:
www.miosito.net?prova%26reg=bis

Store it like this:
<string name="my_url">"www.miosito.net?prova&reg=bis"</string>
Where & is the XML equivelant of the ampersand symbol &.

Percent encoding may do the trick: http://en.wikipedia.org/wiki/Percent-encoding
You'll basically have something like this: www.miosito.net?prova%26reg=bis

You can enclose your url in double quotes, something like :
<string name="my_url">"www.miosito.net?prova&reg=bis"</string>
This is a recommended way to enclose string resources in Android.
Update 1 : Have a look at the following link for more info :
http://developer.android.com/guide/topics/resources/string-resource.html#FormattingAndStyling
Update 2:
#WebnetMobile.com : Correct, indeed :)
'&' is being treated a special character by xml and enclosing in quotes doesn't work. I tried out
www.miosito.net?prova%26reg=bis
and it didn't work out either. I even tried enclosing it in quotes but still didn't work. Am I missing something ?
Meanwhile, the following does work :
<string name="my_url">www.miosito.net%1$sprova%2$sreg=bis</string>
and then in code :
Resources resources=getResources();
String url=String.format(resources.getString(R.string.my_url),"?","&") ;
The '%1$s' and '%2$s' are format specifiers, much like what is used in printf in C. '%1$s' is for strings, '%2$d' is for decimal numbers and so on.

how can i reference something in the /values/strings.xml file programatically?

i had some items in my strings.xml file that i want to change programatically, and originally i was doing it through a setText();call but now i am attempting to translate my app to a different language which means everything needs to be set in my strings.xml file. is it possible to put all the text for my app into a strings.xml and change things programatically through references to the string names, instead of using the setText() function call? for example how would i reference "GrandTotal"?
<string name="GrandTotal">Grand Total:</string>
<string name="choose_prompt">Choose a Mode</string>

You can use setText(R.string.GrandTotal);
If you don't have the possibility to set the text via resId directly you can use getString(R.string.GrandTotal);

To avoid confusion between resourceIds and real ints, you could also use statements like
String s = getResources().getString( R.string.grand_total );
but for most ui methods an overload often provides support for passing directly resourceIds as #Keyboardsurfer said

Try this way . I hope it helps you .
setText(getResources().getString(R.string.GrandTotal));

in an Acrivity:
String str = getString(R.string.choose_prompt);
or
String str = this.getString(R.string.choose_prompt);

Dynamically referencing a String in Strings.xml in Android

Say I have the following my strings.xml file:
<string name="string0">Lorem</string>
<string name="string1">ipsum</string>
<string name="string2">dolor</string>
In my activity an ID is set based on the clicking of a button. If the top button is clicked the id is 0, middle is 1 and bottom button is 2.
What would the syntax look like for referencing one of the three strings?
I know R.string.string0 works but I want to do something equivalent to:
R.string["string"+currentID]
where I derive the string to use based on the ID.
Just not sure what the syntax would look like in Java/Android.
Thanks in advance,
Tony

Could you not just use a string array in your resources instead of separate string entries?

That's a bad approach. It's slow. It'd be better to have an internal integer array with all the R.string IDs.
If you really insist on using a string-based approach, use Resources.getIdentifier().