android - App crash using intent to switch activity -

it's simple login activity when must switch activity, app crash. tried use normal form pubic void onclick() {...} doesn't work.

login.java

package com.example.corrado_mattia_danny.face_offbrains;  import android.app.activity; import android.content.intent; import android.os.bundle; import android.view.menu; import android.view.menuitem; import android.view.view; import android.widget.button; import android.widget.checkedtextview; import android.widget.edittext; import android.widget.toast;   public class login extends activity {      private player player;     private button login;     private edittext username;     private edittext password;      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_login);         login=(button)findviewbyid(r.id.button_sign_in);         username=(edittext)findviewbyid(r.id.nickname);         password=(edittext)findviewbyid(r.id.password);         string = username.gettext().tostring();         string b = password.gettext().tostring();         player.inseriscicredenziali(a,b); //insert player class                                           //username , password         signin();     }      public void signin() {         intent intent = new intent(this, home.class);         startactivity(intent);     } } 

activity_login.xml

<relativelayout     xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:paddingleft="@dimen/activity_horizontal_margin"     android:paddingright="@dimen/activity_horizontal_margin"     android:paddingtop="@dimen/activity_vertical_margin"     tools:context="com.example.corrado_mattia_danny.face_offbrains.login"     android:background="@drawable/sfondo_custom" >       <edittext         android:layout_width="wrap_content"         android:layout_height="35dp"         android:inputtype="textpersonname"         android:hint="nickname"         android:ems="10"         android:id="@+id/nickname"         android:linksclickable="false"         android:textcolor="#ff000000"         android:background="#ffd4d4d4"         android:textstyle="normal|bold|italic"         android:layout_margintop="100dp"         android:layout_alignparenttop="true"         android:layout_centerhorizontal="true" />      <edittext         android:layout_width="wrap_content"         android:layout_height="35dp"         android:inputtype="textpassword"         android:ems="10"         android:id="@+id/password"         android:layout_below="@+id/nickname"         android:layout_alignstart="@+id/nickname"         android:layout_margintop="30dp"         android:hint="password"         android:textcolor="#ff000000"         android:background="#ffd4d4d4"         android:textstyle="normal|bold|italic" />      <button         style="?android:attr/buttonstylesmall"         android:layout_width="50dp"         android:layout_height="50dp"         android:id="@+id/button_sign_in"         android:background="#ffffeb00"         android:layout_centervertical="true"         android:layout_toendof="@+id/nickname"         android:layout_marginleft="10dp"         android:onclick="signin"/>  </relativelayout> 

home.java

the buttons in home doesn't work yet.

package com.example.corrado_mattia_danny.face_offbrains;  import android.app.activity; import android.content.intent; import android.support.v7.app.actionbaractivity; import android.os.bundle; import android.view.menu; import android.view.menuitem; import android.view.view; import android.widget.button;   public class home extends activity {      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_home);         intent intent = getintent();         button bottone_sfida_amico = (button)findviewbyid(r.id.button_sfida_amico);         button bottone_avversario_casuale = (button)findviewbyid(r.id.button_avversario_casuale);     } } 

}

when set method through android:onclick attribute, method signin() must have parameter view, source of event. so, declare method follows:

public void signin(view view) {     ... }