How to use spannable strings in addTextChangedListener to change color of editText substring?

Question

I am trying to implement something similar to a code editor where keywords are automatically highlighted. I am going to have a string array and I want to change the color and font of the editText string when the user types the text and it matches a string from the string array. I am using the addTextChangeListener but the text of the whole editText changes. I want just the matched word to be highlighted.I understand I have to use spannable strings but the code crashes. Can anyone help me with the correct usage of spannable strings with addTextChangedListener() ? Here is my code:

editText.addTextChangedListener(new TextWatcher() {
            private SpannableString spanString;
            private ForegroundColorSpan span;
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            }
            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                spanString = new SpannableString(s);
                span = new ForegroundColorSpan(Color.YELLOW);
                spanString.setSpan(span, start, start + count, 0);
            }
            @Override
            public void afterTextChanged(Editable s) {
                int beginIdx = spanString.getSpanStart(s);
                int endIdx = spanString.getSpanEnd(s);

                if(s.subSequence(beginIdx, endIdx).equals("for"))
                {
                        editText.setText(spanString, EditText.BufferType.SPANNABLE);
                }
                spanString.removeSpan(span);
                span = null;
                spanString = null;
            }
        });

Answer 1

ms1996 I know you are trying to create IDE. To highlight the syntax of codes codes you should use spannable String or use any library to get it easier. Moreover you can try this code :

                    I created simple code for highlight syntax in EditText. First i created a HashMap to store keywords and colors.

                    Map<String,Integer> map = new HashMap<>();
                    map.put("public",Color.CYAN);
                    map.put("void", Color.BLUE);
                    map.put("String",Color.RED);

Then I added a TextWatcher for the EditText. In afterTextChanged method I used following code to set colors to each keyword,

                    ........
                    @Override
                    public void afterTextChanged(Editable editable) {
                        String string = editable.toString();
                        String[] split = string.split("\\s");
                        for(int i = 0 ; i < split.length ; i++){
                            String s = split[i];
                            if(map.containsKey(s)){
                                int index = string.indexOf(s);
                                int color = map.get(s);
                                editable.setSpan(new ForegroundColorSpan(color),
                                        index,
                                        index + s.length(),
                                        Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
                            }

                        }
                    }