How To Display Border To Imageview?

You can create a resource (layer drawable xml) for your ImageView‘s “border” (actually background), and declare in your theme that the ImageView‘s background resource is the drawable xml.

If you need this “border” to be changed based on the ImageView‘s state (focused, selected, etc.), then you should create more layer drawables, and put them together into a selector xml (state drawable).
Then in your theme you should set the ImageView‘s background to be this selector.xml.

Update
Below is a sample of how to specify a simple border to your images, that will result in

You have to

1. create a new layer drawable file (image_border.xml),
2. modify/create your styles.xml file
3. modify/create your colors.xml file
4. modify your layout xml file (or your code) to apply the style to the ImageView.

res/drawable/image_border.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="rectangle">
            <gradient android:angle="90" 
                android:startColor="@color/image_border_start" 
                android:centerColor="@color/image_border_center"
                android:endColor="@color/image_border_end" />
        </shape>
    </item>
    <item android:top="2dp" android:left="2dp" 
        android:right="2dp" android:bottom="2dp">
        <shape android:shape="rectangle">
            <solid android:color="@color/default_back_color" />
        </shape>
    </item>
</layer-list>

res/values/styles.xml
Add the following lines:

<style name="myImageView">
    <!-- 3dp so the background border to be visible -->
    <item name="android:padding">3dp</item>
    <item name="android:background">@drawable/image_border</item>
    <item name="android:scaleType">fitCenter</item>
</style>

res/values/colors.xml
Add the following lines:

<color name="image_border_start">#40990000</color>
<color name="image_border_end">#FF660000</color>
<color name="image_border_center">#FFFF3333</color>

And finally specify the style of your ImageView in your layout xml:

<ImageView android:id="@+id/my_image" 
    android:layout_width="100dp" android:layout_height="100dp"
    android:src="https://stackoverflow.com/questions/5841128/@drawable/efteling"
    style="@style/myImageView" />