title: Android: how do I use Save button click in one Activity to add a CardView item in Recyclerview Activity?
body: <p>I have a UI screen (CardViewActivity) with a bunch of EditText lines for data input for the user.  When the user is done they click the "Save" button on the UI to save the string data input to a CardView that is then added to a RecyclerView list.  When I tried to add the Save button reference (R.id.saveButtonRV) in the Recycler activity (ListContactsActivity), the app crashed due to the Button click.</p>
  
  <pre><code>ListContactsActivity 
  ...
  public class ListContactsActivity extends AppCompatActivity {
  
      private ListContactsAdapter mContactsAdapter;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
  
      final RecyclerView  mRecyclerView;
      ...
      Button saveButton = (Button) findViewById(R.id.saveButtonRV);
      // the below line caused the app to crash with NPE
      saveButton.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View v) {
              Contact contact = new Contact("", "");
              mContactsAdapter.addItem(contact);
              mRecyclerView.scrollToPosition(0);
          }
      });
  
  
  CardViewActivity (for user input)
  ...
  public class CardViewActivity extends AppCompatActivity {   
  
       private ListenerEditText cListenerEditText;
       ...
       public void onClickSave(View v) {
           int stringToDo = cListenerEditText.getText().toString().replace(" ", "").length();
           else if (stringToDo &gt; 0 &amp;&amp; stringNotes1 == 0 &amp;&amp; stringNotes2 == 0 &amp;&amp;
              stringDueDate == 0 &amp;&amp; stringDueTime ==0) {
          cListenerEditText.requestFocus();
          InputMethodManager imm = (InputMethodManager)
                  getSystemService(Context.INPUT_METHOD_SERVICE);
          imm.hideSoftInputFromWindow(cListenerEditText.getWindowToken(), 0);
          cListenerEditText.clearFocus();
          Button saveButton = (Button)findViewById(R.id.saveButtonRV);
          saveButton.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
                 // Can I reference Contact, the adapter and the RecyclerView
                 // here to addItem (the CardView with string data) to the 
                 // ReyclerView list?
              }
          });
      }
  }
  
  
  xml referencing the saveButtonRV
  
  &lt;LinearLayout
  
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:id="@+id/cardviewTwobuttons"
  android:orientation="horizontal" &gt;
  
  &lt;Space
      android:layout_width="0dp"
      android:layout_height="match_parent"
      android:layout_weight="14" /&gt;
  
  &lt;LinearLayout
      android:id="@+id/LinearLayout4"
      android:layout_marginTop="1dp"
      android:layout_width="0dp"
      android:layout_height="wrap_content"
      android:layout_weight="52"
      style="?android:attr/borderlessButtonStyle"
      android:background="@drawable/rect_forbuttons"&gt;
  
      &lt;Button
          android:id="@+id/clearButton"
          android:text="Clear"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_gravity="start|center"
          android:textColor="#FFFFFF"
          android:textStyle="bold"
          style="?android:attr/borderlessButtonStyle"
          android:textAppearance="?android:attr/textAppearanceLarge"
          android:background="@drawable/clearbutton_rounded"
          android:drawableStart="@drawable/ic_clear_white_24dp"
          android:drawableLeft="@drawable/ic_clear_white_24dp"
          android:paddingStart="2dp"
          android:paddingLeft="2dp"
          android:paddingEnd="2dp"
          android:paddingRight="2dp"
          android:layout_marginEnd="12dp"
          android:layout_marginRight="12dp"
          android:layout_marginTop="4dp"
          android:layout_marginBottom="4dp"
          android:onClick="onClickClear"
          android:nextFocusRight="@+id/saveButtonRV"  /&gt;
  
      &lt;Button
          android:id="@+id/saveButtonRV"
          android:text="Save"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_gravity="end|center"
          android:textColor="#FFFFFF"
          android:textStyle="bold"
          style="?android:attr/borderlessButtonStyle"
          android:textAppearance="?android:attr/textAppearanceLarge"
          android:background="@drawable/savebutton_rounded"
          android:drawableStart="@drawable/ic_save_white_24dp"
          android:drawableLeft="@drawable/ic_save_white_24dp"
          android:layout_marginStart="12dp"
          android:layout_marginLeft="12dp"
          android:layout_marginTop="4dp"
          android:layout_marginBottom="4dp"
          android:onClick="onClickSave"  /&gt;
  
  &lt;/LinearLayout&gt;
  
  &lt;Space
      android:layout_width="0dp"
      android:layout_height="match_parent"
      android:layout_weight="14" /&gt;
  </code></pre>
  
  <p></p>
  
  <p>logcat from <strong>ListContactsActivity</strong>:</p>
  
  <pre><code>java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jdw.seventhscreen/com.example.jdw.seventhscreen.ListContactsActivity}: java.lang.NullPointerException
                                                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
                                                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
                                                                                     at android.app.ActivityThread.access$600(ActivityThread.java:130)
                                                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
                                                                                     at android.os.Handler.dispatchMessage(Handler.java:99)
                                                                                     at android.os.Looper.loop(Looper.java:137)
                                                                                     at android.app.ActivityThread.main(ActivityThread.java:4745)
                                                                                     at java.lang.reflect.Method.invokeNative(Native Method)
                                                                                     at java.lang.reflect.Method.invoke(Method.java:511)
                                                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
                                                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
                                                                                     at dalvik.system.NativeStart.main(Native Method)
                                                                                  Caused by: java.lang.NullPointerException
                                                                                     at com.example.jdw.seventhscreen.ListContactsActivity.onCreate(ListContactsActivity.java:58)
                                                                                     at android.app.Activity.performCreate(Activity.java:5008)
                                                                                     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
                                                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
                                                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
                                                                                     at android.app.ActivityThread.access$600(ActivityThread.java:130) 
                                                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
                                                                                     at android.os.Handler.dispatchMessage(Handler.java:99) 
                                                                                     at android.os.Looper.loop(Looper.java:137) 
                                                                                     at android.app.ActivityThread.main(ActivityThread.java:4745) 
                                                                                     at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                                     at java.lang.reflect.Method.invoke(Method.java:511) 
                                                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
                                                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
                                                                                     at dalvik.system.NativeStart.main(Native Method) 
  02-02 23:47:10.529 15871-15871/com.example.jdw.seventhscreen I/Process: Sending signal.   
  </code></pre>