Button button = findViewById(R.id.button) always resolves to null in Android

android

Solution

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.

Problem

I'm new to Android development, 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 ``` <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" /> ``` fragment_main.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" android:paddingBottom="@dimen/activity_vertical_margin" tools:context="com.pluralsight.activitylifecycle.MainActivity$PlaceholderFragment"> <TextView android:text="@string/hello_world" android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/textView" /> <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" /> </RelativeLayout> ```

Original source