xamarin.android - button onclick event dont work in xamarin -

i have problem code. have created button "sign up", want when click on button dialog called "dialog_signup appear.

the problem doesnt appear. , error far

    **2>a numeric comparison attempted on "$(_devicesdkversion)" evaluates "" instead of number, in condition "$(_devicesdkversion) >= 21".     2>build failed.     2>  ========== build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ========== ========== deploy: 0 succeeded, 1 failed, 0 skipped ==========** 

here code

mainactivity.cs

    using system;     using android.app;     using android.content;     using android.runtime;     using android.views;     using android.widget;     using android.os;     using android.content.res;      namespace gamelandplus     {         [activity(label = "gamelandplus", mainlauncher = true, icon = "@drawable/icon")]         public class mainactivity : activity         {             private button mbtnsignup;              protected override void oncreate(bundle bundle)             {                 base.oncreate(bundle);                   setcontentview(resource.layout.main);                  mbtnsignup = findviewbyid<button>(resource.id.btnsignup);                 mbtnsignup.click += (object sender, eventargs args) =>                 {                     fragmenttransaction transaction = fragmentmanager.begintransaction();                     dialog_signup signupdialog = new dialog_signup();                     signupdialog.show(transaction, "dialog fragment");                  };              }              }     } 

-->

main.axml      <?xml version="1.0" encoding="utf-8"?>     <linearlayout xmlns:android="http://schemas.android.com/apk/res/android"         android:orientation="vertical"         android:layout_width="fill_parent"         android:layout_height="fill_parent"         android:background="@android:color/background_light"         android:weightsum="100"         android:minwidth="25px"         android:minheight="25px">         <imageview             android:src="@drawable/images"             android:layout_width="match_parent"             android:layout_weight="20"             android:layout_height="0dp"             android:id="@+id/imageview1" />         <textview             android:text="create account"             android:textappearance="?android:attr/textappearancemedium"             android:layout_width="match_parent"             android:layout_weight="20"             android:layout_height="0dp"             android:textcolor="#000000"             android:id="@+id/createaccount"             android:textsize="35sp"             android:gravity="center"             android:textstyle="bold" />         <button             android:layout_width="match_parent"             android:layout_weight="10"             android:layout_height="0dp"             android:gravity="center"             android:id="@+id/signin"             android:textcolor="#ffffff"             android:background="@drawable/butto1"             android:layout_marginleft="40dp"             android:layout_marginright="40dp"             android:text="sign in"             android:shadowcolor="#a8a8a8"             android:shadowdx="0"             android:shadowdy="0"             android:shadowradius="5" />         <textview             android:text="or"             android:textappearance="?android:attr/textappearancemedium"             android:layout_width="match_parent"             android:layout_weight="15"             android:layout_height="0dp"             android:id="@+id/or"             android:textcolor="#000000"             android:textsize="35sp"             android:gravity="center"             android:textstyle="bold" />         <button             android:text="sign up"             android:layout_width="match_parent"             android:layout_height="0dp"             android:layout_weight="10"             android:id="@+id/btnsignup"             android:textcolor="#ffffff"             android:background="@drawable/butto1"             android:layout_marginleft="40dp"             android:layout_marginright="40dp"             android:shadowcolor="#00ffffff"             android:shadowradius="5"             android:drawableright="@drawable/goodmess" />         <relativelayout             android:layout_width="match_parent"             android:layout_height="0dp"             android:layout_weight="35"             android:minheight="15px"             android:minwidth="15px">             <progressbar                 android:layout_width="wrap_content"                 android:layout_height="wrap_content"                 android:id="@+id/progressbar1"                 android:background="@drawable/progressbar"                 android:indeterminate="true"                 android:layout_centerinparent="true" />         </relativelayout>     </linearlayout> 

-->

the dialog page want pop when click on button

dialogsignup.axml

 <?xml version="1.0" encoding="utf-8"?> <relativelayout xmlns:android="http://schemas.android.com/apk/res/android"     android:background="#f1f3f4"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     android:minheight="300dp"     android:minwidth="300dp">     <edittext         android:inputtype="textpersonname"         android:layout_width="match_parent"         android:layout_height="40dp"         android:id="@+id/firstname"         android:background="@drawable/editstyle"         android:layout_marginbottom="10dp"         android:layout_marginleft="20dp"         android:layout_marginright="20dp"         android:layout_margintop="25dp"         android:hint="username"         android:paddingleft="10dp"         android:paddingright="10dp"         android:textcolor="#000" />     <edittext         android:layout_below="@+id/firstname"         android:inputtype="textemailaddress"         android:layout_width="match_parent"         android:layout_height="40dp"         android:id="@+id/textemail"         android:background="@drawable/editstyle"         android:layout_marginbottom="10dp"         android:layout_marginleft="20dp"         android:layout_marginright="20dp"         android:hint="email/phone number"         android:paddingleft="10dp"         android:paddingright="10dp"         android:textcolor="#000" />     <edittext         android:layout_below="@+id/textemail"         android:inputtype="textpassword"         android:layout_width="match_parent"         android:layout_height="40dp"         android:id="@+id/password"         android:background="@drawable/editstyle"         android:layout_marginbottom="10dp"         android:layout_marginleft="20dp"         android:layout_marginright="20dp"         android:hint="password"         android:paddingleft="10dp"         android:paddingright="10dp"         android:textcolor="#000" />     <button         android:layout_below="@+id/password"         android:text="sign up"         android:layout_width="match_parent"         android:layout_height="50dp"         android:id="@+id/btndialogemail"         android:textcolor="#ffffff"         android:background="@drawable/butto1"         android:layout_marginleft="40dp"         android:layout_marginright="40dp"         android:shadowcolor="#00ffffff"         android:shadowradius="5"         android:drawableright="@drawable/goodmess" /> </relativelayout> 

-->

and dialog_signup.cs

using android.views; using android.widget;  namespace gamelandplus {     class dialog_signup:dialogfragment     {         public override view oncreateview(layoutinflater inflater, viewgroup container, bundle saveinstancestate)         {             base.oncreateview(inflater, container, saveinstancestate);             var view = inflater.inflate(resource.layout.dialogsignup, container, false);             return view;         }         public override void onactivitycreated(bundle savedinstancestate)         {             dialog.window.requestfeature(windowfeatures.notitle);//set title             base.onactivitycreated(savedinstancestate);             dialog.window.attributes.windowanimations = resource.style.dialog_animation;         }     } } 

--> not include slideup/slideright/butto1 because drawable file. please can u check on it. change emulator far. dont know problem. suggestion?