当我打开基本活动时，应用程序崩溃了

Question

我最近开始学习android，我正在使用带有'fab'按钮的基本活动作为默认名称。

这是我的java文件

   public class AddNewMember extends AppCompatActivity {

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_add_new_member);
            Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
            setSupportActionBar(toolbar);

            FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
            fab.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Intent intent = new Intent(AddNewMember.this, HomeScreen.class);
                    startActivity(intent);
                }
            });
        }

    }

fab按钮将用户直接带到主屏幕。但活动崩溃说了以下几行

 FATAL EXCEPTION: main
                                             Process: com.adt.alphadev.rotarydist3132, PID: 3361
                                             java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getVisibility()' on a null object reference
                                                 at android.widget.LinearLayout.forceUniformHeight(LinearLayout.java:1380)
                                                 at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1368)
                                                 at android.widget.TableRow.onMeasure(TableRow.java:114)
                                                 at android.view.View.measure(View.java:17547)
                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                 at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
                                                 at android.widget.TableLayout.measureChildBeforeLayout(TableLayout.java:464)
                                                 at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
                                                 at android.widget.TableLayout.measureVertical(TableLayout.java:476)
                                                 at android.widget.TableLayout.onMeasure(TableLayout.java:439)
                                                 at android.view.View.measure(View.java:17547)
                                                 at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:727)
                                                 at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:463)
                                                 at android.view.View.measure(View.java:17547)
                                                 at android.widget.ScrollView.measureChildWithMargins(ScrollView.java:1260)
                                                 at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
                                                 at android.widget.ScrollView.onMeasure(ScrollView.java:337)
                                                 at android.view.View.measure(View.java:17547)
                                                 at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:727)
                                                 at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:463)
                                                 at android.view.View.measure(View.java:17547)
                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                 at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:669)
                                                 at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:89)
                                                 at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1319)
                                                 at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:734)
                                                 at android.view.View.measure(View.java:17547)
                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                 at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
                                                 at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
                                                 at android.view.View.measure(View.java:17547)
                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                 at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
                                                 at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
                                                 at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
                                                 at android.view.View.measure(View.java:17547)
                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                 at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
                                                 at android.view.View.measure(View.java:17547)
                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                 at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
                                                 at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
                                                 at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
                                                 at android.view.View.measure(View.java:17547)
                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                 at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
                                                 at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2615)
                                                 at android.view.View.measure(View.java:17547)
                                                 at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2015)
                                                 at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1173)
                                                 at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1379)
                                                 at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1061)
                                                 at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5885)
                                                 at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
                                                 at android.view.Choreographer.doCallbacks(Choreographer.java:580)
                                                at android.view.Choreographer.doFrame(Choreographer.java

添加新会员活动

<?xml version="1.0" encoding="utf-8"?>

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/AppTheme.AppBarOverlay">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay" />

</android.support.design.widget.AppBarLayout>

<include layout="@layout/content_add_new_member" />

<android.support.design.widget.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:layout_margin="@dimen/fab_margin"
    android:src="@mipmap/ic_home_black_24dp" />

主屏幕java文件

public class HomeScreen extends AppCompatActivity {

ImageButton btn_dashboard, btn_reporting,btn_apply_credits,btn_upload_bulletin,btn_view_rank;
ImageButton btn_add_new_member,btn_update_club_details,btn_view_projects,btn_view_members,btn_view_notifications,btn_change_password,btn_logout;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_home_screen);
  btn_add_new_member = (ImageButton)findViewById(R.id.btn_add_new_member);
  btn_add_new_member.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(new Intent(HomeScreen.this, AddNewMember.class));
            startActivity(intent);
        }
    }); 


  }
}

请帮忙！