Button button findViewById R id button always resolves to null in Android Studio

Question

I m new to Android development and Android Studio  so pardon my ignorance    findViewById of a button I added always resolves to null  Hence if I try to setonClickListener it fails the whole Activity   MainActivity    public class MainActivity extends ActionBarActivity         Override     protected void onCreate Bundle savedInstanceState            super onCreate savedInstanceState           setContentView R layout activity main            if  savedInstanceState    null                getSupportFragmentManager   beginTransaction                        add R id container  new PlaceholderFragment                         commit                       Button buttonClick    Button  findViewById R id button           buttonClick setOnClickListener new View OnClickListener                  Override             public void onClick View view                    onButtonClick  Button  view                                          public void onButtonClick Button view            TextView textHello    TextView  findViewById R id textView           textHello setText  Clicked                     Override     public boolean onCreateOptionsMenu Menu menu                Inflate the menu  this adds items to the action bar if it is present          getMenuInflater   inflate R menu main  menu           return true              Override     public boolean onOptionsItemSelected MenuItem item               Handle action bar item clicks here  The action bar will            automatically handle clicks on the Home Up button  so long            as you specify a parent activity in AndroidManifest xml          int id   item getItemId            if  id    R id action settings                return true                    return super onOptionsItemSelected item                         A placeholder fragment containing a simple view              public static class PlaceholderFragment extends Fragment            public PlaceholderFragment                         Override         public View onCreateView LayoutInflater inflater  ViewGroup container                  Bundle savedInstanceState                View rootView   inflater inflate R layout fragment main  container  false               return rootView                       activity main xml   lt FrameLayout xmlns android  http   schemas android com apk res android  xmlns tools  http   schemas android com tools  android id    id container  android layout width  match parent  android layout height  match parent  tools context  com pluralsight activitylifecycle MainActivity  tools ignore  MergeRootFrame    gt    fragment main xml   lt 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  android paddingBottom   dimen activity vertical margin  tools context  com pluralsight activitylifecycle MainActivity PlaceholderFragment  gt    lt TextView     android text   string hello world      android layout width  wrap content      android layout height  wrap content      android id    id textView    gt    lt Button     android layout width  wrap content      android layout height  wrap content      android text   string buttonClick      android id    id button      android layout below    id textView      android layout alignParentRight  true      android layout alignParentEnd  true      android layout marginRight  54dp    gt    lt  RelativeLayout gt

User · Answer

The button code should be moved to the PlaceholderFragment   class  There you will call the layout fragment main xml in the onCreateView method  Like so   Override public View onCreateView LayoutInflater inflater  ViewGroup container          Bundle savedInstanceState        View view   inflater inflate R layout fragment main  container  false       Button buttonClick    Button  view findViewById R id button       buttonClick setOnClickListener new View OnClickListener              Override         public void onClick View view                onButtonClick  Button  view                           return view

User · Answer

This is because findViewById   searches in the activity main layout  while the button is located in the fragment s layout fragment main   Move that piece of code in the onCreateView   method of the fragment          View rootView   inflater inflate R layout fragment main  container  false   Button buttonClick    Button rootView findViewById R id button   buttonClick setOnClickListener new View OnClickListener          Override     public void onClick View view            onButtonClick  Button  view               Notice that now you access it through rootView view   Button buttonClick    Button rootView findViewById R id button     otherwise you would get again NullPointerException

User · Answer

R id button is not part of R layout activity main  How should the activity find it in the content view   The layout that contains the button is displayed by the Fragment  so you have to get the Button there  in the Fragment

[android] Button button = findViewById(R.id.button) always resolves to null in Android Studio

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