How to get UnderlineSpan with another color in Android?

Question

I'd like to have Spannable that looks like error in IDEs - underline with another color.

I've tried to create ColorUnderlineSpan class that extends android UnderlineSpan, but it makes all the text another color (i need to add colored underline only):

/**
 * Underline Span with color
 */
public class ColorUnderlineSpan extends android.text.style.UnderlineSpan {

    private int underlineColor;

    public ColorUnderlineSpan(int underlineColor) {
        super();
        this.underlineColor = underlineColor;
    }

    @Override
    public void updateDrawState(TextPaint ds) {
        super.updateDrawState(ds);
        ds.setColor(underlineColor);
    }
}

I've also found DynamicDrawableSpan class but i can't see canvas bounds to draw to.

It would be great to get any Spannable impl with abstract draw method with bounds argument.

Answer 1

This isn't the prettiest solution, but it ended up working for me:

public class CustomUnderlineSpan implements LineBackgroundSpan {

int color;
Paint p;
int start, end;
public CustomUnderlineSpan(int underlineColor, int underlineStart, int underlineEnd) {
    super();
    color = underlineColor;
    this.start = underlineStart;
    this.end = underlineEnd;
    p = new Paint();
    p.setColor(color);
    p.setStrokeWidth(3F);
    p.setStyle(Paint.Style.FILL_AND_STROKE);
}

@Override
public void drawBackground(Canvas c, Paint p, int left, int right, int top, int baseline, int bottom, CharSequence text, int start, int end, int lnum) {

    if (this.end < start) return;
    if (this.start > end) return;

    int offsetX = 0;
    if (this.start > start) {
        offsetX = (int)p.measureText(text.subSequence(start, this.start).toString());
    }

    int length = (int)p.measureText(text.subSequence(Math.max(start, this.start), Math.min(end, this.end)).toString());
    c.drawLine(offsetX, baseline + 3F, length + offsetX, baseline + 3F, this.p);
}

It's weird because you have to specify the character index to start and end your underlining with, but it worked for me.

Answer 2

The answer @korbonix posted works fine. I've made some improvements in Kotlin and supporting multiline TextViews:

class ColorUnderlineSpan(val underlineColor: Int, val underlineStart: Int, val underlineEnd: Int): LineBackgroundSpan {

    val paint = Paint()

    init {
        paint.color = underlineColor
        paint.strokeWidth = 3.0f
        paint.style = Paint.Style.FILL_AND_STROKE
    }

    override fun drawBackground(c: Canvas?, p: Paint?, left: Int, right: Int, top: Int, baseline: Int, bottom: Int, text: CharSequence?, start: Int, end: Int, lnum: Int) {
        if (!(underlineStart < underlineEnd)) {
            throw Error("underlineEnd should be greater than underlineStart")
        }

        if (underlineStart > end || underlineEnd < start) {
            return
        }

        var offsetX = 0

        if (underlineStart > start) {
            offsetX = p?.measureText(text?.subSequence(start, underlineStart).toString())?.toInt() ?: 0
        }

        val length: Int = p?.measureText(text?.subSequence(Math.max(start, underlineStart), Math.min(end, underlineEnd)).toString())?.toInt()
            ?: 0

        c?.drawLine(offsetX.toFloat(), baseline + 3.0f, (length + offsetX).toFloat(), baseline + 3.0f, paint)
    }
}

And here is a sample usage. textText is the TextView. The text is 127 characters long and it underlines from the position 112 to the 127.

Important: For reasons I don't fully understand the span length should be set to the full length of the text. Otherwise the component doesn't even get called. Feel free to educate me on why's that.

    // Sets link color
    val spannable = SpannableString(getString(R.string.forgot_text))
    spannable.setSpan(
            ColorUnderlineSpan(Color.RED), 112, 127),
            0, 127, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE)
    textText.text = spannable