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>
FindViewById<T>(Int32) Finds a view that was identified by the id attribute from the XML layout resource.
findViewById is the method that finds the View by the ID it is given. So findViewById(R. id. myName) finds the View with name 'myName'.
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project. Step 2 − Add the following code to res/layout/activity_main. xml.
. findViewById(R. id. retry) would always return null.
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.
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;
}
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With