Style bottom Line in Android

It's kind of a hack, but I think this is probably the best way to do it. The dashed line will always be on the bottom, regardless of the height.

<layer-list xmlns:android="http://schemas.android.com/apk/res/android">

    <item>
        <shape android:shape="rectangle" >
            <solid android:color="#1bd4f6" />
        </shape>
    </item>

    <item android:top="-2dp" android:right="-2dp" android:left="-2dp">
        <shape>
            <solid android:color="@android:color/transparent" />
            <stroke
                android:dashGap="10px"
                android:dashWidth="10px"
                android:width="1dp"
                android:color="#ababb2" />
        </shape>
    </item>

</layer-list>

Explanation:

The second shape is transparent rectangle with a dashed outline. The key in making the border only appear along the bottom lies in the negative margins set the other sides. These negative margins "push" the dashed line outside the drawn area on those sides, leaving only the line along the bottom. One potential side-effect (which I haven't tried) is that, for views that draw outside their own bounds, the negative-margin borders may become visible.

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:top="-6dp"
        android:left="-6dp"
        android:right="-6dp"
        android:bottom="0dp">

        <shape android:shape="rectangle">
            <solid android:color="#88FFFF00"/>
            <stroke
                android:width="5dp"
                android:color="#FF000000"/>
        </shape>
    </item>
</layer-list>

This does the trick...

<item >
    <shape android:shape="rectangle">
        <solid android:color="#YOUR_BOTTOM_LINE_COLOR"/>
    </shape>
</item>

<item android:bottom="1.5dp">
    <shape android:shape="rectangle">
        <solid android:color="#YOUR_BG_COLOR"/>
    </shape>
</item>

I feel it is straightforward, without all this negative paddings or storks.

<layer-list xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:drawable="@color/main_bg_color"/>
    <item android:gravity="bottom">
        <shape android:shape="rectangle">
            <size android:height="5dp"/>
            <solid android:color="@color/bottom_bar_color"/>
        </shape>
    </item>
</layer-list>

This answer is for those google searchers who want to show dotted bottom border of EditText like here

Create dotted.xml inside drawable folder and paste these

<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:bottom="1dp"
        android:left="-2dp"
        android:right="-2dp"
        android:top="-2dp">
        <shape android:shape="rectangle">
            <stroke
                android:width="0.5dp"
                android:color="@android:color/black" />    
            <solid android:color="#ffffff" />
            <stroke
                android:width="1dp"
                android:color="#030310"
                android:dashGap="5dp"
                android:dashWidth="5dp" />
            <padding
                android:bottom="5dp"
                android:left="5dp"
                android:right="5dp"
                android:top="5dp" />
        </shape>
    </item>
</layer-list>

Then simply set the android:background attribute to dotted.xml we just created. Your EditText looks like this.

<EditText
    android:id="@+id/editText"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Some Text"
    android:background="@drawable/dotted" />