android gridview row dividers / separators

If you are using custom layout for grid items. Below code will work.

Step 1: Give background color to GridView

This is going to serve as a divider.
Give horizontalSpacing and verticalSpacing as 1dp
backgroundColor will be your divider color.

<GridView
        android:id="@+id/gridView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="#e5e5e5"
        android:horizontalSpacing="1dp"
        android:numColumns="auto_fit"
        android:stretchMode="columnWidth"
        android:verticalSpacing="1dp" >

Step 2: Give background color to Custom Grid Item Layout

This is going to serve as a foreground color for GridItems.
In my case I kept it white (#fff)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    android:background="#fff"
    android:padding="15dp"
     >

    <ImageView
        android:id="@+id/icon"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:src="https://stackoverflow.com/questions/12109126/@drawable/ic_launcher_transparent" />

    <TextView
        android:id="@+id/lable"
        android:layout_marginTop="5dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Medium Text"
        android:textStyle="bold"
        android:textColor="#D0583B"
        android:textAppearance="?android:attr/textAppearanceSmall" />

</LinearLayout>

Result

Note:
If you do not want vertical separator, keep horizontalSpacing = 0dp
If you do not want horizontal separator, keep verticalSpacing = 0dp