android - How to underline text in TextView with some different color than that of text?

Question

I know how to underline text in a textview. But how to underline text with some different color ? Underline can be done with:

TextView t = (TextView) findViewById(R.id.textview);
t.setPaintFlags(t.getPaintFlags() | Paint.UNDERLINE_TEXT_FLAG);
t.setText("Underline Text");

Let say my textcolor is black and I want to underline the same with blue color, how to do it ? Thanks in advance.

Answer 1

I had the same problem and I have stumbled upon Layout class when reading some other posts for doing this on EditText. It provides everything you need to make this happen by manually drawing underline with canvas.

First I defined custom attributes for an easy customization in XML layout files

<declare-styleable name="UnderlinedTextView" >
    <attr name="underlineHeight" format="dimension" />
    <attr name="underlineOffset" format="dimension" />
    <attr name="underlineColor" format="color" />
    <attr name="underLinePosition" format="enum">
        <enum name="baseline" value="0" />
        <enum name="below" value="1" />
    </attr>
</declare-styleable>

And a custom TextView class

   class UnderlinedTextView @JvmOverloads constructor(
    context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
) : androidx.appcompat.widget.AppCompatTextView(context, attrs, defStyleAttr) {

    @Retention(AnnotationRetention.SOURCE)
    @IntDef(POSITION_BASELINE, POSITION_BELOW)
    annotation class UnderLinePosition {
        companion object {
            const val POSITION_BASELINE = 0
            const val POSITION_BELOW = 1
        }
    }

    private val linePaint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
        style = Paint.Style.FILL
    }

    var lineColor: Int
        get() = linePaint.color
        set(value) {
            if (linePaint.color != value) {
                linePaint.color = value
                invalidate()
            }
        }

    var lineHeight: Float
        get() = linePaint.strokeWidth
        set(value) {
            if (linePaint.strokeWidth != value) {
                linePaint.strokeWidth = value
                updateSpacing()
            }
        }

    var lineTopOffset = 0F
        set(value) {
            if (field != value) {
                field = value
                updateSpacing()
            }
        }

    @UnderLinePosition
    var linePosition = POSITION_BASELINE

    private val rect = Rect()

    private var internalAdd: Float = lineSpacingExtra

    private inline val extraSpace
        get() = lineTopOffset + lineHeight

    init {
        val density = context.resources.displayMetrics.density

        val typedArray = context.obtainStyledAttributes(attrs, R.styleable.UnderlinedTextView, defStyleAttr, 0)
        lineColor = typedArray.getColor(R.styleable.UnderlinedTextView_underlineColor, currentTextColor)
        lineTopOffset = typedArray.getDimension(R.styleable.UnderlinedTextView_underlineOffset, 0f)
        lineHeight = typedArray.getDimension(R.styleable.UnderlinedTextView_underlineHeight, density * 1)
        linePosition = typedArray.getInt(R.styleable.UnderlinedTextView_underLinePosition, POSITION_BASELINE)
        typedArray.recycle()
    }

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec)
        setMeasuredDimension(measuredWidth, measuredHeight + (extraSpace + 0.5f).toInt())
    }

    override fun onDraw(canvas: Canvas?) {
        canvas?.takeIf { !text.isNullOrEmpty() }?.let {
            val count = lineCount
            val layout = layout
            var xStart: Float
            var xStop: Float
            var yStart: Float
            var firstCharInLine: Int
            var lastCharInLine: Int
            var lastLine: Boolean
            var offset: Int
            val lineSpacing = lineSpacingExtra * lineSpacingMultiplier
            for (i in 0 until count) {
                val baseline = getLineBounds(i, rect)
                lastLine = i == count - 1
                offset = if (lastLine) 0 else 1
                firstCharInLine = layout.getLineStart(i)
                lastCharInLine = layout.getLineEnd(i)
                xStart = layout.getPrimaryHorizontal(firstCharInLine)
                xStop = layout.getPrimaryHorizontal(lastCharInLine - offset)
                yStart = when (linePosition) {
                    POSITION_BASELINE -> baseline + lineTopOffset
                    POSITION_BELOW -> (rect.bottom + lineTopOffset) - if (lastLine) 0F else lineSpacing
                    else -> throw NotImplementedError("")
                }
                canvas.drawRect(xStart, yStart, xStop, yStart + lineHeight, linePaint)
            }
        }
        super.onDraw(canvas)
    }

    private fun updateSpacing() {
        setLineSpacing(internalAdd, 1f)
    }

    override fun setLineSpacing(add: Float, mult: Float) {
        internalAdd = add
        super.setLineSpacing(add + extraSpace, 1f)
    }
}

Then it's usage is simple

<some.package.UnderlinedTextView
    android:id="@+id/tvTest"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_marginBottom="10dp"
    android:layout_marginLeft="20dp"
    android:layout_marginRight="20dp"
    android:gravity="center"
    android:text="This is a demo text"
    android:textSize="16sp"
    app:underlineColor="#ffc112ef"
    app:underlineHeight="3dp"/>

Final result

• Multi line
  
  
• Single line