android - How can I align an imagebutton under anothe one? -

i have 3 imagebuttons inside horizontal linearlayout , want add 1 more imagebutton right under left imagebutton(when left imagebutton starts , finishes, want same thing imagebutton under that). in vertital linearlayout. cannot align down imagebutton vertically one. how can that? ideas?

my code this:

android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical">  <linearlayout     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:orientation="horizontal"     android:layout_margintop="20dp"     android:gravity="center">      <imagebutton         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:id="@+id/imagebutton11"         android:background="@drawable/image"         android:layout_gravity="center"         android:layout_marginright="30dp"/>      <imagebutton         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:id="@+id/imagebutton12"         android:background="@drawable/image"         android:layout_gravity="center"         android:layout_marginright="30dp"/>      <imagebutton         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:id="@+id/imagebutton13"         android:background="@drawable/image"         android:layout_gravity="center"         android:layout_marginright="30dp"/> </linearlayout>  <linearlayout     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:orientation="horizontal"     android:layout_margintop="20dp"     android:gravity="left">      <imagebutton         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:id="@+id/imagebutton14"         android:background="@drawable/image"         android:layout_marginright="30dp"/>  </linearlayout> 

you can more relativelayout via tablelayout or linearlayout. if willing use fixed widths imagebuttons (which should not problem imagebuttons), here 1 layout solve problem.
(i have used buttons in layout below sake of simplicity, work same imagebuttons well.)

<?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="match_parent"     android:gravity="center_horizontal">     <button         android:layout_width="120dp"         android:layout_height="wrap_content"         android:id="@+id/btn1"         android:text="button1" />     <button         android:layout_width="120dp"         android:layout_height="wrap_content"         android:id="@+id/btn2"         android:layout_torightof="@id/btn1"         android:text="button2" />     <button         android:layout_width="120dp"         android:layout_height="wrap_content"         android:id="@+id/btn3"         android:layout_torightof="@id/btn2"         android:text="button3" />      <button         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="button4"         android:id="@+id/btn4"         android:layout_below="@id/btn1"         android:layout_alignleft="@id/btn1"         android:layout_alignright="@id/btn1"/> </relativelayout> 

here how look: