ImageView, why different size?

Question

First thing, I know many people have asked same thing, but this one is nearly same but I have few more questions.

I have an image of 48px x 48px, so if I set this image in ImageView with

layout_width="wrap_content"
layout_height="wrap_content"

then image looks bigger but if I use following fixed size, it gets smaller

layout_width="48dp"
layout_height="48dp"

I think it's now showing properly(not pixelated ?) with 48dp, but why it got bigger if I use wrap_content ? And if the image size through wrap_content is correct then whats the point of using dp(if it make image smaller) ?

Answer 1

48dp (or 48dip) stands for "Density Independent Pixel". This means that the physical size of the image as displayed on the screen of an Android should be the same regardless of screen density and size. In order to support this, Android adjusts the actual pixel size displayed based on screen density. Your findings of different sizes will vary from device to device.

The conversion of dp units to screen pixels is: pixels = dps * (density / 160). For example, on 240 dpi screen, 1dp would equal 1.5 physical pixels. Using dp units to define your application’s UI is highly recommended, as a way of ensuring proper display of your UI on different screens.

Answer 2

This probably happens because you don't explicitly set the scaleType. Set your scaleType in XML as follows and you should be fine:

android:scaleType="center"

Answer 3

Try this

<ImageView
    android:id="@+id/seprator2"
    layout_width="48dp"
    layout_height="48dp"
    android:scaleType="fitXY"
    android:src="@drawable/your_image" />

And if still it shows small then your image must contains alpha around it.