Get absolute position for a given offset on TextView (Android)

Question

I have a TextView in which I want to place a solid color block over given words of the TextView, for example:

"This is a text string, I want to put a rectangle over this WORD" - so, "WORD" would have a rectangle with a solid color over it.

To do this, I am thinking about overriding the onDraw(Canvas canvas) method, in order to draw a block over the text. My only problem is to find an efficient way to get the absolute position of a given word or character.

Basically, I am looking for something that does the exact opposite of the getOffsetForPosition(float x, float y) method

Answer 1

Based on this post: How get coordinate of a ClickableSpan inside a TextView?, I managed to use this code in order to put a rectangle on top of the text:

protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    Paint paint = new Paint();
    paint.setStyle(Paint.Style.FILL);
    paint.setColor(Color.WHITE);

    // Initialize global value
    TextView parentTextView = this;
    Rect parentTextViewRect = new Rect();

    // Find where the WORD is
    String targetWord = "WORD";
    int startOffsetOfClickedText = this.getText().toString().indexOf(targetWord);
    int endOffsetOfClickedText = startOffsetOfClickedText + targetWord.length();

    // Initialize values for the computing of clickedText position
    Layout textViewLayout = parentTextView.getLayout();

    double startXCoordinatesOfClickedText = textViewLayout.getPrimaryHorizontal((int)startOffsetOfClickedText);
    double endXCoordinatesOfClickedText = textViewLayout.getPrimaryHorizontal((int)endOffsetOfClickedText);

    // Get the rectangle of the clicked text
    int currentLineStartOffset = textViewLayout.getLineForOffset((int)startOffsetOfClickedText);
    int currentLineEndOffset = textViewLayout.getLineForOffset((int)endOffsetOfClickedText);
    boolean keywordIsInMultiLine = currentLineStartOffset != currentLineEndOffset;
    textViewLayout.getLineBounds(currentLineStartOffset, parentTextViewRect);

    // Update the rectangle position to his real position on screen
    int[] parentTextViewLocation = {0,0};
    parentTextView.getLocationOnScreen(parentTextViewLocation);

    double parentTextViewTopAndBottomOffset = (
        //parentTextViewLocation[1] - 
        parentTextView.getScrollY() + 
        parentTextView.getCompoundPaddingTop()
    );

    parentTextViewRect.top += parentTextViewTopAndBottomOffset;
    parentTextViewRect.bottom += parentTextViewTopAndBottomOffset;

    // In the case of multi line text, we have to choose what rectangle take
    if (keywordIsInMultiLine){

        WindowManager wm = (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
        Display display = wm.getDefaultDisplay();

        int screenHeight = display.getHeight();
        int dyTop = parentTextViewRect.top;
        int dyBottom = screenHeight - parentTextViewRect.bottom;
        boolean onTop = dyTop > dyBottom;

        if (onTop){
            endXCoordinatesOfClickedText = textViewLayout.getLineRight(currentLineStartOffset);
        }
        else{
            parentTextViewRect = new Rect();
            textViewLayout.getLineBounds(currentLineEndOffset, parentTextViewRect);
            parentTextViewRect.top += parentTextViewTopAndBottomOffset;
            parentTextViewRect.bottom += parentTextViewTopAndBottomOffset;
            startXCoordinatesOfClickedText = textViewLayout.getLineLeft(currentLineEndOffset);
        }

    }

    parentTextViewRect.left += (
        parentTextViewLocation[0] +
        startXCoordinatesOfClickedText + 
        parentTextView.getCompoundPaddingLeft() - 
        parentTextView.getScrollX()
    );
    parentTextViewRect.right = (int) (
        parentTextViewRect.left + 
        endXCoordinatesOfClickedText - 
        startXCoordinatesOfClickedText
    );

    canvas.drawRect(parentTextViewRect, paint);
 }