I am trying to get the state of a Switch widget. To do this I create a new variable like so :
Switch notifSwitch = findViewById(R.id.notif_switch).
However that does not work because now notifSwitch is null and casting setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() gets me a java.lang.NullPointerException.
I suspect it has to do with the fact that the widget with the 'notif_switch' id (the Switch that I am trying to get the value of) is not (directly) in activity_main.xml, which is the layout I am passing to setContentView at the beginning of my onCreate method because if I add setContentView(R.layout.line_notif); before the Switchdeclaration, the code works fine. The app only consists of what is in the line_notif.xmllayout, which is only the Switch and a TextView, but at least I don't have any errors and I am able to get the state of the Switch widget.
I do not know how to access the widget from my MainActivity.javafile and cannot find a way to do so. I tried looking at as many posts as possible before making my own. I am sorry if I missed one that answers my question but I just cannot find a way to solve this problem and would really appreciate the help.
Thank you.
MainActivity.java:
...
@RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN)
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
private MainActivity activity;
private boolean notificationsOn=false;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
this.activity = this;
...
// HERE IS THE PROBLEM
Switch notifSwitch = findViewById(R.id.notif_switch); // notifSwitch = null
// Error on next line
notifSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
if (isChecked) {
notificationsOn = true;
Toast.makeText(getApplicationContext(), "Notifications enabled", Toast.LENGTH_SHORT).show();
} else {
notificationsOn = false;
Toast.makeText(getApplicationContext(), "Notifications disabled", Toast.LENGTH_SHORT).show();
}
}
});
}
...
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
android:background="@color/colorPrimary"
tools:openDrawer="start">
<include
layout="@layout/app_bar_main"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<android.support.design.widget.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="@layout/nav_header_main"
app:menu="@menu/activity_main_drawer"
android:background="@color/colorPrimary"/>
</android.support.v4.widget.DrawerLayout>
activity_main_drawer.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
tools:showIn="navigation_view"
...>
...
<item
android:id="@+id/nav_notifications"
app:actionLayout="@layout/line_notif"
android:enabled="true"
tools:ignore="MenuTitle" />
...
</menu>
line_notif.xml
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:id="@+id/line_notif"
android:background="@android:color/transparent">
...
<Switch
android:id="@+id/notif_switch"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="end"
android:theme="@style/SwitchTheme"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:paddingTop="15dp"/>
</RelativeLayout>
Full error :
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.projectname/com.example.projectname.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Switch.setOnCheckedChangeListener(android.widget.CompoundButton$OnCheckedChangeListener)' on a null object reference
