textview - issue with my first android app -

before posting question , wanna clarify first post on stackoverflow , let's story beggin.

as title said , i'm making first app on android , found myself blocked issue .

there 3 button on app : button1 : give textview2 "hello world again " , make visible // button2 : make textview2 invisible // button3 : make textview1 invisible

this code freom main_activity :

package com.example.ismail.app_test_1; 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; import android.widget.edittext; import android.widget.textview;   public class mainactivity extends actionbaractivity { button button_aff; button button_hide; button button_hide_hw;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     button_aff = (button) findviewbyid(r.id.button);     button_hide = (button) findviewbyid(r.id.button2);     button_hide_hw = (button) findviewbyid(r.id.button3);     button_aff.setonclicklistener(new view.onclicklistener() {         public void onclick(view v) {             show("hello world again");         }     });     button_hide.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             hide();         }     });     button_hide_hw.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             hide_hw();         }      }); }  public void show(string str) {     textview text;     text = (textview) findviewbyid(r.id.textview2);     text.setvisibility(view.visible);     text.settext(str);     setcontentview(text);  }  public void hide() {     textview text;     text = (textview) findviewbyid(r.id.textview2);     text.setvisibility(view.invisible);     setcontentview(text); } public void hide_hw() {     textview text;     text = (textview) findviewbyid(r.id.textview);     text.setvisibility(view.invisible);     setcontentview(text); } } 

after getting on phone , when touch button : "unfortunatly,app_test_1 has stopped ! can me ?

edit : removed setcontentview , works , lot guys. if has tuto me improve android programming skills i'm taker

do not use setcontentview() method outside of oncreate() delete in show , hide functions. should work probably