android - Cannot add Button in second child in Sliding up Panel -

i have sliding panel in layout. there button in first child works fine when add button in second child there nullpointerexception thrown. if remove button layout works fine. not able understand doing wrong?

layout looks :

<linearlayout      xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:orientation="vertical">      <com.sothree.slidinguppanel.slidinguppanellayout          xmlns:sothree="http://schemas.android.com/apk/res-auto"         android:id="@+id/sliding_layout"         android:layout_width="match_parent"         android:layout_height="match_parent"         android:gravity="bottom"         sothree:umanopanelheight="68dp"         sothree:umanoshadowheight="4dp">          <linearlayout             android:layout_width="match_parent"             android:layout_height="match_parent"             android:orientation="vertical">              <textview                 android:layout_width="wrap_content"                 android:layout_height="wrap_content"                 android:gravity="center|top"                 android:text="the awesome sliding panel"                 android:textsize="16sp" />              <button                 android:id="@+id/toggle_upper"                 android:layout_width="wrap_content"                 android:layout_height="wrap_content"                 android:text="upper" />         </linearlayout>          <linearlayout             android:layout_width="match_parent"             android:layout_height="match_parent"             android:orientation="vertical">              <edittext                 android:layout_width="wrap_content"                 android:layout_height="wrap_content"                 android:hint="edit this" />              <button                 android:id="@+id/toggle_upper2"                 android:layout_width="wrap_content"                 android:layout_height="wrap_content"                 android:text="upper" />          </linearlayout>     </com.sothree.slidinguppanel.slidinguppanellayout> </linearlayout> 

exception:

java.lang.nullpointerexception     @ android.view.viewgroup_delegate.drawshadow(viewgroup_delegate.java:74)     @ android.view.viewgroup_delegate.drawchild(viewgroup_delegate.java:61)     @ android.view.viewgroup.drawchild(viewgroup.java:3404)     @ android.view.viewgroup.dispatchdraw(viewgroup.java:3198)     @ android.view.view.draw(view.java:15017)     @ android.view.viewgroup.drawchild_original(viewgroup.java:3404)     @ android.view.viewgroup_delegate.drawchild(viewgroup_delegate.java:53)     @ android.view.viewgroup.drawchild(viewgroup.java:3404)     @ com.sothree.slidinguppanel.slidinguppanellayout.drawchild(slidinguppanellayout.java:1024)     @ android.view.viewgroup.dispatchdraw(viewgroup.java:3198)     @ android.view.view.draw(view.java:15017)     @ android.view.viewgroup.drawchild_original(viewgroup.java:3404)     @ android.view.viewgroup_delegate.drawchild(viewgroup_delegate.java:53)     @ android.view.viewgroup.drawchild(viewgroup.java:3404)     @ android.view.viewgroup.dispatchdraw(viewgroup.java:3198)     @ android.view.view.draw(view.java:15017)     @ android.view.viewgroup.drawchild_original(viewgroup.java:3404)     @ android.view.viewgroup_delegate.drawchild(viewgroup_delegate.java:53)     @ android.view.viewgroup.drawchild(viewgroup.java:3404)     @ android.view.viewgroup.dispatchdraw(viewgroup.java:3198)     @ android.view.view.draw(view.java:15017)     @ android.view.viewgroup.drawchild_original(viewgroup.java:3404)     @ android.view.viewgroup_delegate.drawchild(viewgroup_delegate.java:53)     @ android.view.viewgroup.drawchild(viewgroup.java:3404)     @ android.view.viewgroup.dispatchdraw(viewgroup.java:3198)     @ android.view.view.draw(view.java:15117)     @ android.view.view.draw(view.java:15022)     @ android.view.viewgroup.drawchild_original(viewgroup.java:3404)     @ android.view.viewgroup_delegate.drawchild(viewgroup_delegate.java:53)     @ android.view.viewgroup.drawchild(viewgroup.java:3404)     @ android.view.viewgroup.dispatchdraw(viewgroup.java:3198)     @ android.view.view.draw(view.java:15117)     @ com.android.layoutlib.bridge.impl.rendersessionimpl.render(rendersessionimpl.java:587)     @ com.android.layoutlib.bridge.bridge.createsession(bridge.java:334)     @ com.android.ide.common.rendering.layoutlibrary.createsession(layoutlibrary.java:350)     @ com.android.tools.idea.rendering.renderservice$5.compute(renderservice.java:688)     @ com.android.tools.idea.rendering.renderservice$5.compute(renderservice.java:677)     @ com.intellij.openapi.application.impl.applicationimpl.runreadaction(applicationimpl.java:932)     @ com.android.tools.idea.rendering.renderservice.createrendersession(renderservice.java:677)     @ com.android.tools.idea.rendering.renderservice.render(renderservice.java:815)     @ org.jetbrains.android.uipreview.androidlayoutpreviewtoolwindowmanager.dorender(androidlayoutpreviewtoolwindowmanager.java:646)     @ org.jetbrains.android.uipreview.androidlayoutpreviewtoolwindowmanager.access$1700(androidlayoutpreviewtoolwindowmanager.java:82)     @ org.jetbrains.android.uipreview.androidlayoutpreviewtoolwindowmanager$7$1.run(androidlayoutpreviewtoolwindowmanager.java:589)     @ com.intellij.openapi.progress.impl.progressmanagerimpl$2.run(progressmanagerimpl.java:178)     @ com.intellij.openapi.progress.progressmanager.executeprocessunderprogress(progressmanager.java:209)     @ com.intellij.openapi.progress.impl.progressmanagerimpl.executeprocessunderprogress(progressmanagerimpl.java:212)     @ com.intellij.openapi.progress.impl.progressmanagerimpl.runprocess(progressmanagerimpl.java:171)     @ org.jetbrains.android.uipreview.androidlayoutpreviewtoolwindowmanager$7.run(androidlayoutpreviewtoolwindowmanager.java:584)     @ com.intellij.util.ui.update.mergingupdatequeue.execute(mergingupdatequeue.java:320)     @ com.intellij.util.ui.update.mergingupdatequeue.execute(mergingupdatequeue.java:310)     @ com.intellij.util.ui.update.mergingupdatequeue$2.run(mergingupdatequeue.java:254)     @ com.intellij.util.ui.update.mergingupdatequeue.flush(mergingupdatequeue.java:269)     @ com.intellij.util.ui.update.mergingupdatequeue.flush(mergingupdatequeue.java:227)     @ com.intellij.util.ui.update.mergingupdatequeue.run(mergingupdatequeue.java:217)     @ com.intellij.util.concurrency.queueprocessor.runsafely(queueprocessor.java:238)     @ com.intellij.util.alarm$request$1.run(alarm.java:327)     @ java.util.concurrent.executors$runnableadapter.call(executors.java:471)     @ java.util.concurrent.futuretask.run(futuretask.java:262)     @ java.util.concurrent.threadpoolexecutor.runworker(threadpoolexecutor.java:1145)     @ java.util.concurrent.threadpoolexecutor$worker.run(threadpoolexecutor.java:615)     @ java.lang.thread.run(thread.java:745) 

i running old version of android studio. android studio 1.0 not support preview of layout.

i updated android studio , can see layout now.