Check out example codes for "add close button on right top corner of alert dialog box for android". It will help you in understanding the concepts better.

Code Example 1

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="400dp"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="10dp"
        android:layout_marginRight="10dp"
        android:layout_marginTop="15dp"
        android:background="#F4F4F4">

        <!--Main Body of your custom dialog-->
    </RelativeLayout>

    <LinearLayout
        android:id="@+id/llTop"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:orientation="vertical">

        <ImageButton
            android:id="@+id/btnCancel"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/btnBookK"
            android:background="@null"
            android:src="@drawable/ic_close" />

    </LinearLayout>

</RelativeLayout>

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