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Change the color of a part of a TextView in strings.xml

In my android app with Kotlin, I created a layout in which there's a TextView that shows some text. For the text I have an item in strings.xml where I want to change the color of part of this Text, I tried the following code :
<string name="description">the product is <font fgcolor="green"> free </font></string>
But, The color didn't change.
I just want to change the color of "free" to green, can someone explain how I can achieve this?

Use <font color="#008000">free</font> instead. According to the documentation, the correct attribute name is color and it only supports hex codes.

Ben P.'s awesome answer should satisfy your use case. However, I want to present to you another way you can achieve this.
You can use SpannableString to achieve the same effect. With SpannableString, you can set several behaviours (color, font-weight, font-size, click-behaviour, etc) to any part of your String.
For the string in your question, you can do something like this:
// the textview you want to set your coloured text to
TextView textView = (TextView) findViewById(R.id.myTextView);
// declare the string you want to span as a Spannable
Spannable wordtoSpan = new SpannableString("the product is free");
// set the colour span
wordtoSpan.setSpan(new ForegroundColorSpan(Color.GREEN), 15, 19, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
// set the text to your TextView
textView.setText(wordtoSpan);

Android EditText: how to apply spans when composing?

How can I apply spans on EditText text when the user is composing?
For example the user has activated "bold" when composing, so every character input since then should be bold.
I thought about adding text change listener to the EditText and update the text as the user composes, but I wanna know if there's a better way of doing this.

The question was already answered in the comments, but to make it more permanent I will add a fuller answer.
In order to set a span (like Bold) wherever the user is composing, you just set a span on the text at the cursor (or selection) position.
StyleSpan boldSpan = new StyleSpan(Typeface.BOLD);
int start = editText.getSelectionStart();
int end = editText.getSelectionEnd();
int flag = Spannable.SPAN_INCLUSIVE_INCLUSIVE;
editText.getText().setSpan(boldSpan, start, end, flag);
The SPAN_INCLUSIVE_INCLUSIVE flag means that any text added before or after the span will be included in the span, even if the text length is 0 when the span is added.
See also
How to set other types of spans
Meaning of the Spannable flags

You can use the text watcher, and set the span in the editable that you receive in the afterTextChanged() method, I'm currently writing a rich text editor and this is the approach I've used with styles, and it works quite well, however, so far I haven't been able to set the spans that requires the paragraphs like quoteSpan, or bulletSpan.
But if you just want simple styles like italics, or bold etc., you can use this approach.

Change word color in resource string

Is there anyway to set the color of a string resource in android? I mean, I know I can use some html tags to change string style (or substrings) but have not found any to change color. I have seen other solutions here at stackoverflow like passing the string to Html.fromHtml(string) before setting the text but I want to do it in the string resource editor. Any possibility?

It looks like this method is working:
<string name="some_text">this is <font fgcolor="#ffff0000">red</font></string>

As far as I know it is not possible. I would use a SpannableString to change the color.
int colorBlue = getResources().getColor(R.color.blue);
String text = getString(R.string.text);
SpannableString spannable = new SpannableString(text);
// here we set the color
spannable.setSpan(new ForegroundColorSpan(colorBlue), 0, text.length(), 0);
Spannable is really nice. You can set thinks like fontseize and stuff there and just attach it to a text view. The advantage is that you can have different colors in one view.
Edit: Ok, if you only want to set the Color the solution mentioned above me is the way to go.

The strings themselves have no color, but you can change the color of the text in the textView they appear in. See the textview documentation, but there are 2 ways to do it.
XML
android:textColor
Code
setTextColor(int)

I have recently made a flexible solution for this problem. It enables me of easily add multiple styles to substrings by using method chaining. It makes use of the SpannableString. When you want to give a certain substring a color, you can use ForegroundColorSpan.
public StyledString putColor(String subString, #ColorRes int colorRes){
if(getStartEnd(subString)){
int color = ColorUtil.getColor(context, colorRes);
ForegroundColorSpan foregroundColorSpan = new ForegroundColorSpan(color);
fullStringBuilder.setSpan(foregroundColorSpan, startingIndex, endingIndex, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
}
return this;
}
For full code see gist.

Multi Formatted TextView

I'm trying to have the layout of the comments on a progam in the following form:
I want the USER_NAME in Bold, and the DATE in Enphasis (The red part should be normal, I don't want it red). My problem comes with the red part. I cant get the cooment to be displayed like this using layouts, I've been able to get:
and
Is there any way to get the comment working like the one I'm showing. I've thought about a multi formatted textView, is it posible??
If getting the comment like this is not possible, just say it's imposible.

One possible solution is to put two TextViews into a Linear layout one after another and then use SpannableStringBuilder to assign the formatted text to the first view.
SpannableStringBuilder sb = new SpannableStringBuilder();
sb.append(text);
sb.setSpan(createBoldSpan(), 0, lengthOf(userName),
Spannable.SPAN_INCLUSIVE_EXCLUSIVE);
firstTextView.setText(sb, TextView.BufferType.NORMAL);
createBoldSpan should return TextAppearanceSpan
private TextAppearanceSpan userNameSpanInBold(String userName) {
return new TextAppearanceSpan(...);
}
please follow API docs for TextAppearanceSpan - you can create one using custom style.

You could use a WebView with loadData if HTML markup would be good, or alternatively delve into the realm of Spannable text.
I've not worked with Spannable text myself, but essentially it allows you to attach attributes (e.g. styles & colors) to parts of text in a TextView.
The relevant method is TextView.setText(CharSequence text, TextView.BufferType type) with BufferType of SPANNABLE. The documentation I've seen is.... confusing.

How do you change the textcolor of the list items in an AlertDialog

Hello I am trying to change the text color of the items in a list on a ListPreference pop up window. I have spent over an hour looking through all of the various style names but I can't find TextAppearance or anything that goes to this particular text. Thanks for your help!

You can't and you shouldn't. *Preference uses styles from com.android.internal.R.styleable which might be changed by manufactures. The idea of using the default ones is that every preference screen in your device look alike.
On the other hand you can try doing an Activity with android:theme="#android:style/Theme.Dialog" in your app's AndroidManifest and place a ListView styled as you want.

I don't really know which kind of View use ListPreference, probably it's something like TextView. If so than you could make smth like:
TextView textView;
String myString;
//....
SpannableString spanString=new SpannableString(myString);
spanString.setSpan(new ForegroundColorSpan(Color.RED), 0, myString.length(), Spanned.SPAN_INCLUSIVE_INCLUSIVE);
textView.setText(spanString);