显示OptionsMenu时出现NullPointerException

我需要以编程方式创建菜单（与选项卡列表完全相同），以在应用程序中启用导航功能。所以我做了这样的代码

public override bool OnCreateOptionsMenu (IMenu menu)
{
    base.OnCreateOptionsMenu (menu);
    for (int i = 0; i < fragmentsTabs.Count; i++) {
        menu.Add(0,100 + i,i,new Java.Lang.String(fragmentsTabs.GetItem(i).Key));
    }
    return true;
}

但是，当我单击菜单按钮时，我得到一个类似的异常：

[AndroidRuntime] java.lang.NullPointerException
[AndroidRuntime]    at android.support.v7.internal.view.menu.ListMenuItemView.setTitle(ListMenuItemView.java:117)
[AndroidRuntime]    at android.support.v7.internal.view.menu.ListMenuItemView.initialize(ListMenuItemView.java:104)
[AndroidRuntime]    at android.support.v7.internal.view.menu.MenuPopupHelper$MenuAdapter.getView(MenuPopupHelper.java:377)
[AndroidRuntime]    at android.support.v7.internal.view.menu.MenuPopupHelper.measureContentWidth(MenuPopupHelper.java:219)
[AndroidRuntime]    at android.support.v7.internal.view.menu.MenuPopupHelper.tryShow(MenuPopupHelper.java:153)
[AndroidRuntime]    at android.support.v7.widget.ActionMenuPresenter$OpenOverflowRunnable.run(ActionMenuPresenter.java:752)
[AndroidRuntime]    at android.os.Handler.handleCallback(Handler.java:733)
[AndroidRuntime]    at android.os.Handler.dispatchMessage(Handler.java:95)
[AndroidRuntime]    at android.os.Looper.loop(Looper.java:136)
[AndroidRuntime]    at android.app.ActivityThread.main(ActivityThread.java:5017)
[AndroidRuntime]    at java.lang.reflect.Method.invokeNative(Native Method)
[AndroidRuntime]    at java.lang.reflect.Method.invoke(Method.java:515)
[AndroidRuntime]    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
[AndroidRuntime]    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
[AndroidRuntime]    at dalvik.system.NativeStart.main(Native Method)
[AndroidRuntime]    at android.support.v7.internal.view.menu.MenuPopupHel08.448 W/ActivityManager(  575):   Force finishing activity pl.media30.android.parlament/aplikacjaparlamentandroid.PersonDetailsActivity

我正在使用支持库中的工具栏：

Toolbar = FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
SetSupportActionBar(Toolbar);
SupportActionBar.SetHomeButtonEnabled(true);
SupportActionBar.SetDisplayHomeAsUpEnabled(true);

在另一部手机上，我获得了有关NullPointerException的更多信息：

[AndroidRuntime] java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
[AndroidRuntime]    at android.support.v7.internal.view.menu.ListMenuItemView.setTitle(ListMenuItemView.java:117)
[AndroidRuntime]    at android.support.v7.internal.view.menu.ListMenuItemView.initialize(ListMenuItemView.java:104)
[AndroidRuntime]    at android.support.v7.internal.view.menu.MenuPopupHelper$MenuAdapter.getView(MenuPopupHelper.java:377)
[AndroidRuntime]    at android.support.v7.internal.view.menu.MenuPopupHelper.measureContentWidth(MenuPopupHelper.java:219)
[AndroidRuntime]    at android.support.v7.internal.view.menu.MenuPopupHelper.tryShow(MenuPopupHelper.java:153)
[AndroidRuntime]    at android.support.v7.widget.ActionMenuPresenter$OpenOverflowRunnable.run(ActionMenuPresenter.java:752)
[AndroidRuntime]    at android.os.Handler.handleCallback(Handler.java:739)
[AndroidRuntime]    at android.os.Handler.dispatchMessage(Handler.java:95)
[AndroidRuntime]    at android.os.Looper.loop(Looper.java:135)
[AndroidRuntime]    at android.app.ActivityThread.main(ActivityThread.java:5221)
[AndroidRuntime]    at java.lang.reflect.Method.invoke(Native Method)
[AndroidRuntime]    at java.lang.reflect.Method.invoke(Method.java:372)
[AndroidRuntime]    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
[AndroidRuntime]    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

有人知道为什么不创建TextView吗？可能是个问题。我在此活动中有很多片段，但没有一个是使用菜单。如果我创建单个图标，例如搜索，则一切正常。图标已正确创建，并且onclick得到了很好的处理。仅当菜单项未显示为动作时，问题才会出现

@编辑

我的工具栏axml是：

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:minHeight="?attr/actionBarSize"
    android:background="?attr/colorPrimary">
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="end"
        android:scaleType="fitEnd"
        android:src="@drawable/side" />
</android.support.v7.widget.Toolbar>