How to get a string from attr with reference format type?

Question

I have my custom attr.xml document in which I specified declare-styleable:

Answer 1

There's an excellent general answer which I recommend you to refer to: Declaring a custom android UI element using XML

In particular, you should use Context.obtainStyledAttributes(AttributeSet set, int[] attrs) and TypedArray.getString(int index) instead of AttributeSet.getAttributeValue(...):

TypedArray ta = activityContext.obtainStyledAttributes(attrs, R.styleable.EditTextValidateablePreference);
String theString = ta.getString(R.styleable.EditTextValidateablePreference_errorMessage);
ta.recycle();