Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference

Question

My app is crashing even though I instantiated my buttons to my activity. What am I doing wrong? Here is my xml and java code. Please help me I really need help right now. I don't know what to do. Here is my error stack:

Process: com.example.dith.finalproject3, PID: 9301
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dith.finalproject3/com.example.dith.finalproject3.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
        at com.example.dith.finalproject3.MainActivity.expansions(MainActivity.java:193)
        at com.example.dith.finalproject3.MainActivity.onCreate(MainActivity.java:63)
        at android.app.Activity.performCreate(Activity.java:7136)
        at android.app.Activity.performCreate(Activity.java:7127)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)

Here is my java code:

public void expansions()
{
        btnCalendar = (ImageButton) findViewById(R.id.btnCalendar);
        btnCalendarHide = (Button) findViewById(R.id.btnCalendarHide);
        expCalendar = (View) findViewById(R.id.expCalendar);
        expCalendar.setVisibility(View.INVISIBLE);
}

Written below is my XML file:

<LinearLayout
                        android:id="@+id/expCalendar"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content"
                        android:orientation="vertical">

                        <TextView
                            android:id="@+id/txtCalendar"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:padding="@dimen/spacing_large"
                            android:text="Calendar Placeholder" />

                        <View
                            android:layout_width="match_parent"
                            android:layout_height="1dp"
                            android:background="@color/grey_10" />

                        <LinearLayout
                            android:layout_width="match_parent"
                            android:layout_height="wrap_content"
                            android:gravity="end"
                            android:orientation="horizontal">

                            <Button
                                android:id="@+id/btnCalendarHide"
                                style="@style/Widget.AppCompat.Button.Borderless"
                                android:layout_width="wrap_content"
                                android:layout_height="wrap_content"
                                android:gravity="center"
                                android:text="HIDE" />

                        </LinearLayout>

Thank you very much enjoy your day!

Answer 1

Your problem is here:

    expCalendar = (View) findViewById(R.id.expCalendar);
    expCalendar.setVisibility(View.INVISIBLE);

The findViewById method is returning null . This means expCalendar is null , which means you're trying to call the setVisibility method on an object that doesn't exist. The straightforward answer is to check expCalendar for nullity before you use it:

    expCalendar = (View) findViewById(R.id.expCalendar);
    if (expCalendar != null){
        expCalendar.setVisibility(View.INVISIBLE);
    }

However, that doesn't address the implied question as to whether you care about expCalendar not being found at all. Unfortunately I don't know enough about Android to help you with that one.