Develop Reference

Why we should not change content of returned value from TextView#getText()?

Android Docs in about TextView.getText() say:
Note: The content of the return value should not be modified. If you want a modifiable one, you should make your own copy first.
Also TextView has setText (CharSequence text, TextView.BufferType type) method and you can pass TextView.BufferType.EDITABLE to it to enable casting result of getText() method to an Editable. As Docs say the purpose of Editable interface is:
This is the interface for text whose content and markup can be changed [...]
My question is: If we can pass Editable to the TextView and get it, why we should not modify it?

Preserve text case when replacing based on case-insensitive search?

In my app I have a Textview with some text. I'm trying to get an input from the user, and then highlight words in the Textview according to that input.
For instance if the text is
Hello stackoverflow
and the input for the user is
hello
I want to replace the text with:
<font color='red'>Hello</font>` stackoverflow
This is my code:
String input = //GETTING INPUT FROM THE USER
text= text.replaceAll(input,"<font color='red'>"+input+"</font>");
Textview.setText(Html.fromHtml(text));
And the replacement is working, but the problem is that my current code changes the original word cases, for example :
Text: HeLLo stackoverflow
Input: hello
What i get: <font color='red'>hello</font> stackoverflow
What i want: <font color='red'>HeLLo</font> stackoverflow

You have to think about regular expressions.
replaceAll allows you to use regular expressions, and so, you can replace the text for the exact occurrence that was found.
For instance if Hello was found, it replaces it for <font color='red'>Hello</font>.
If HeLLo is found, it replaces it for <font color='red'>HeLLo</font>
Your code should be somehing as easy as:
String highlighted = text.replaceAll("(?i)("+input+")","<font color='red'>$1</font>");
This means:
(?i) : i want to search for something, case insensitive
"("+input+")" : input is betwen ( and ) because we are creating a group, so this group can be refered later
"<font color='red'>$1</font>" : instead of replacing by input, that would change the case, we replace it by `$1, that is the reference to the first matched group. This means that we want to replace it using the exact word that was found.
But please, try it and keep playing since regular expressions are tricky.
Other reads
It is easier and more clear if you use the Patternclass.
You can read more here:
http://developer.android.com/reference/java/util/regex/Pattern.html
Also, you can take a look at how to do it:
http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#replaceAll%28java.lang.String,%20java.lang.String%29
public String replaceAll(String regex, String replacement)
.
Replaces each substring of this string that matches the given regular expression with the given replacement.
An invocation of this method of the form str.replaceAll(regex, repl) yields exactly the same result as the expression
Pattern.compile(regex).matcher(str).replaceAll(repl)
Note that backslashes () and dollar signs ($) in the replacement string may cause the results to be different than if it were being treated as a literal replacement string; see Matcher.replaceAll. Use Matcher.quoteReplacement(java.lang.String) to suppress the special meaning of these characters, if desired.
Parameters:
regex - the regular expression to which this string is to be matched
replacement - the string to be substituted for each match
Returns:
The resulting String
UPDATE
You can test your regular expressions in this page:
http://www.regexplanet.com/advanced/java/index.html

Android EditText - Capitalize first letter of sentences using setText()

Folks,
I need to capitalize first letter of every sentence. I followed the solution posted here
First letter capitalization for EditText
It works if I use the keyboard. However, if I use setText() to programatically add text to my EditText, first letter of sentences are not capitalized.
What am I missing? Is there a easy way to fix or do I need to write code to capitalize first letters in my string before setting it to EditText.

The only thing the inputType flag does is suggest to the input method (e.g. keyboard) what the user is attempting to enter. It has nothing to do with the internals of text editing in the EditText view itself, and input methods are not required to support this flag.
If you need to enforce sentence case, you'll need to write a method which does this for you, and run your text through this method before applying it.

You can use substring to make this
private String capSentences( final String text ) {
return text.substring( 0, 1 ).toUpperCase() + text.substring( 1 ).toLowerCase();
}

Setting inputType doesn't affect anything put into the field programmatically. Thankfully, programmatically capitalizing the first letter is pretty easy anyway.
public static String capFirstLetter(String input) {
return input.substring(0,1).toUpperCase() + input.substring(1,input.length());
}

How to search for exact word in a big Message?

How to search for one word in a big message in Android?
I have a text like "The sun always shines above the clouds". I wanna search for a single word, like "sun", and change it to an image. How to do this? Is there any way?

String word = "cat";
String text = "The cat is on the table";
Boolean found;
found = text.contains(word);

Regular Expressions in Java are the most flexible and powerful tools you can use to search and replace strings within other strings. Depending on where you display this data (eg. an HTML View perhaps?) you can replace the words with markup that can display an image or find the location in the string where you can break up elements to create TextViews vs ImageViews. On this latter case, another useful method within the String class might be the indexOf() or contains() methods.

To find the position of a given word in a string use the method
public int indexOf (String string)
For replacing strings with other strings you can use
public String replaceAll (String regularExpression, String replacement)
It is not clear what you mean with "I wanna search for single word like (sun) and change to an image"

An easy way is to use the String.replace method:
String source="The (sun) is shining.";
String replaced=source.replace('(sun)', '<img href="a_sun.png">');
See: http://javarevisited.blogspot.se/2011/12/java-string-replace-example-tutorial.html

The use of input type in EditText

Even if I set the input type to numberdecimal or number, I have to cast the number to get the number. Then what is the use of input type in EditText views.
e.g.
int a = Integer.valueOf(editText.getText().toString());
One more thing, why do I need to use toString() with almost every views to get Text? In java, we could just getText anything from controls.

You have to parse Text to Integer because it doesn't return int. It returns Editable formatted by input type. So if you set input type to numbers you get Editable which contains only numbers.
And you have to add toString() because EditText return Editables not Strings.

InputType is used for various purposes. For example, in a password field, it can hide the characters.
Here's the official description of every single property it can take:
https://developer.android.com/reference/android/widget/TextView.html#attr_android:inputType
As for the second part of your question, EditText.getText() returns Editable
This defines a common interface for all text whose content and markup can be changed (as opposed to immutable text like Strings).
So you need to use toString() to get a string out of it.