android imagebutton can not show ,layout file is following -

  <linearlayout xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:paddingleft="16dp"     android:paddingright="16dp"     android:orientation="vertical" >      <textview         android:layout_width="wrap_content"         android:layout_height="220dp"         android:text="@string/hello_world" />      <relativelayout          android:layout_width="match_parent"         android:layout_height="50dp"         android:paddingleft="16dp"         android:paddingright="16dp"          android:paddingtop="500dp">           <imagebutton             android:id="@+id/id_button_previous"             android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:background="@drawable/previous"             android:contentdescription="@string/text_previous" />          <imagebutton             android:id="@+id/id_button_startpause"             android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:layout_torightof="@id/id_button_previous"             android:layout_marginleft="30dp"             android:background="@drawable/startstop"             android:contentdescription="@string/text_startpause" />          <imagebutton              android:id="@+id/id_button_next"             android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:layout_torightof="@id/id_button_startpause"             android:background="@drawable/next"             android:contentdescription="@string/text_next"             />      </relativelayout>     </linearlayout> 

the layout can show textview 'helloworld',but couldn't show imagebutton,

i don't know why couldn't show normally,where error. if don't write more , can't submmit,this useless.by way ,

oops, such big padding,

android:paddingtop="500dp" 

in here,

 <relativelayout          android:layout_width="match_parent"         android:layout_height="50dp"         android:paddingleft="16dp"         android:paddingright="16dp"          android:paddingtop="500dp"> 

remove padding or resize padding of reative layout smaller value. like,

android:paddingtop="50dp" 

modified code,

 <relativelayout          android:layout_width="match_parent"         android:layout_height="50dp"         android:paddingleft="16dp"         android:paddingright="16dp"          android:paddingtop="50dp"> 

and works, see images..