how to use dp for size in custom drawable

Question

I have defined the custom drawable below:

class HexDrawable constructor(val text: String) : Drawable() {

    private val paint = Paint()

    init {
        paint.color = Color.WHITE
        paint.textSize = 22f
        paint.isAntiAlias = true
        paint.isFakeBoldText = true
        paint.setShadowLayer(3f, 0f, 0f, Color.BLACK)
        paint.style = Paint.Style.FILL

    }

    override fun draw(canvas: Canvas) {
        val width: Int = 120
        val height: Int = 120
        val radius: Float = Math.min(width, height).toFloat() / 2f

        // Draw a green circle in the center
        canvas.drawCircle((width / 2).toFloat(), (height / 2).toFloat(), radius, paint)
    }

    override fun setAlpha(alpha: Int) {
        paint.alpha = alpha
    }

    override fun setColorFilter(colorFilter: ColorFilter?) {
        paint.colorFilter = colorFilter
    }

    override fun getOpacity(): Int {
        return PixelFormat.OPAQUE
    }
}

I am not sure what units the drawable is using. I want to use eg 40dp for the width but the 120 that is specified in the code above turns out very small when it is drawn on the screen so I donlt think it is dp, maybe it is mm?

can someone please clarify what unit it is using by default? and how to use dp instead?

"can someone please clarify what unit it is using by default?" -- I believe that those are in pixels. "how to use dp instead?" -- ideally, whatever code is creating this `HexDrawable` would pass in the size to use in pixels. It, in turn could get that size from a dimension resource, which would handle all of the conversion from other units (e.g., `dp`) to pixels for you. — CommonsWare, Apr 14 '21 at 23:15
this drawable is being used inside an imageview which has "Wrap_Content" for both the width and height, i'd like this custom drawable to be able to mandate the dp width and height.. is there a way to do that? — afgfdg, Apr 14 '21 at 23:21

Wizard · Answer 1 · 2021-04-14T23:42:12.110

By default Android uses "px" for view size.

Here is the converter function.

import android.content.Context
import android.content.res.Resources
import android.util.DisplayMetrics

/**
* Provides utilities for metrics.
*
* Original at:
* @see <a href="https://stackoverflow.com/a/9563438/8877070">stack overflow answer</a>
*
* @author kevin
*/
object MetricsUtil {

    /**
    * This method converts dp unit to equivalent pixels, depending on device density.
    * @param dp A value in dp (density independent pixels) unit. Which we need to convert into pixels
    * @param context Context to get resources and device specific display metrics. If you don't have
    * access to Context, just pass null.
    * @return A float value to represent px equivalent to dp depending on device density
    */
    fun convertDpToPixel(dp: Float, context: Context?): Float {
        return if (context != null) {
            val resources = context.resources
            val metrics = resources.displayMetrics
            dp * (metrics.densityDpi.toFloat() / DisplayMetrics.DENSITY_DEFAULT)
        } else {
            val metrics = Resources.getSystem().displayMetrics
            dp * (metrics.densityDpi.toFloat() / DisplayMetrics.DENSITY_DEFAULT)
        }
    }

    /**
    * This method converts device specific pixels to density independent pixels.
    * @param px A value in px (pixels) unit. Which we need to convert into db
    * @param context Context to get resources and device specific display metrics. If you don't have
    * access to Context, just pass null.
    * @return A float value to represent dp equivalent to px value
    */
    fun convertPixelsToDp(px: Float, context: Context?): Float {
        return if (context != null) {
            val resources = context.resources
            val metrics = resources.displayMetrics
            px / (metrics.densityDpi.toFloat() / DisplayMetrics.DENSITY_DEFAULT)
        } else {
            val metrics = Resources.getSystem().displayMetrics
            px / (metrics.densityDpi.toFloat() / DisplayMetrics.DENSITY_DEFAULT)
        }
    }
}

So you can convert 120 to "dp" value by using above code. Here is other function for converting.

fun Int.toDp(): Int = (this / Resources.getSystem().displayMetrics.density).toInt()
fun Int.toPx(): Int = (this * Resources.getSystem().displayMetrics.density).toInt()

Here is other function for converting. fun Int.toDp(): Int = (this / Resources.getSystem().displayMetrics.density).toInt() fun Int.toPx(): Int = (this * Resources.getSystem().displayMetrics.density).toInt() — Wizard, Apr 14 '21 at 23:37

how to use dp for size in custom drawable

1 Answers1