android - 4 rows of Buttons in LinearLayout fill screen width -

i have vertical linearlayout 4 horizontal linearlayouts. each horizontal layout contains 4 buttons. want buttons in each horizontal linearlayout fill screen width evenly. looks this:

the first button of each row takes width , other 3 buttons per row not visible. know how can fix this?

<linearlayout      android:id = "@+id/ll_screen_bttns"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_margintop="20dp"     android:orientation="vertical"     > <linearlayout      android:id="@+id/ll1"     android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:orientation="horizontal"     android:layout_weight = "1">         <button             android:id="@+id/button0"             android:layout_width="fill_parent"             android:layout_height="@dimen/size"             android:background="@drawable/button"             android:onclick="buttononclick"              android:tag="0"/         />           <button             android:id="@+id/button1"             android:layout_width="fill_parent"             android:layout_height="@dimen/size"             android:background="@drawable/button"             android:onclick="buttononclick"              android:tag="0"             />          <button             android:id="@+id/button2"             android:layout_width="fill_parent"             android:layout_height="@dimen/size"             android:background="@drawable/button"             android:onclick="buttononclick"              android:tag="0"             />          <button             android:id="@+id/button3"             android:layout_width="fill_parent"             android:layout_height="@dimen/size"             android:background="@drawable/button"             android:onclick="buttononclick"              android:tag="0"             />     </linearlayout>  <linearlayout      android:id="@+id/ll2"     android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:orientation="horizontal"     android:layout_weight = "1">     <button         android:id="@+id/button4"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"         />      <button         android:id="@+id/button5"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"        />      <button         android:id="@+id/button6"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"         />      <button         android:id="@+id/button7"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"         />  </linearlayout>  <linearlayout      android:id="@+id/ll3"     android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:orientation="horizontal"     android:layout_weight = "1">     <button         android:id="@+id/button8"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"       />      <button         android:id="@+id/button9"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"         />      <button         android:id="@+id/button10"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"         />      <button         android:id="@+id/button11"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"         /> </linearlayout>  <linearlayout  android:id="@+id/ll4" android:layout_width="fill_parent" android:layout_height="wrap_content" android:orientation="horizontal" android:layout_weight = "1">     <button         android:id="@+id/button12"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"         />      <button         android:id="@+id/button13"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"         />      <button         android:id="@+id/button14"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"         />      <button         android:id="@+id/button15"         android:layout_width="fill_parent"         android:layout_height="@dimen/size"         android:background="@drawable/button"         android:onclick="buttononclick"          android:tag="0"         />      </linearlayout> </linearlayout> 

abstract xml:

<linearlayout     xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:orientation="vertical">      <linearlayout          android:layout_width="match_parent"         android:layout_height="wrap_content"         android:orientation="horizontal">          <button             android:layout_width="0dp"             android:layout_height="@dimen/size"             android:layout_weight="1" />          <button             android:layout_width="0dp"             android:layout_height="@dimen/size"             android:layout_weight="1" />          <button             android:layout_width="0dp"             android:layout_height="@dimen/size"             android:layout_weight="1" />          <button             android:layout_width="0dp"             android:layout_height="@dimen/size"             android:layout_weight="1" />      </linearlayout>        .     .     .  </linearlayout>