Java Android片段工具栏文本未更改

我正在开发一个带有

片段的应用程序。当我打开导航抽屉中未列出的
片段时。例如，我有8个片段，其中7个片段列在导航抽屉中，另一个未列在导航抽屉中（
Fragment
name是子类别
Fragment
）。我可以使用下面的代码更改7
Fragment
的工具栏标题。但我无法更改未在导航抽屉中列出的
Fragment
的工具栏标题

My
HomeActivity.java

public class HomeActivity extends AppCompatActivity implements FragmentDrawer.FragmentDrawerListener {
    private Toolbar mToolbar;
    private FragmentDrawer drawerFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        mToolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(mToolbar);
        getSupportActionBar().setDisplayShowHomeEnabled(true);
        drawerFragment = (FragmentDrawer)
                getSupportFragmentManager().findFragmentById(R.id.fragment_navigation_drawer);
        drawerFragment.setUp(R.id.fragment_navigation_drawer, (DrawerLayout) findViewById(R.id.drawer_layout), mToolbar);
        drawerFragment.setDrawerListener(this);

        displayView(0);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public void onDrawerItemSelected(View view, int position) {
        displayView(position);
    }

    public void displayView(int position) {
        Fragment fragment = null;
        String title = getString(R.string.app_name);
        switch (position) {
            case 0:
                fragment = new HomeFragment();
                title = getString(R.string.title_home);
                Log.d("LOGTAG", "Home");
                break;
            case 1:
                fragment = new CategoriesFragment();
                title = getString(R.string.title_categories);
                Log.d("LOGTAG", "Categories");
                break;
            case 2:
                fragment = new MyOrdersFragment();
                title = getString(R.string.title_myorders);
                Log.d("LOGTAG", "My Orders");
                break;
            case 3:
                fragment = new WalletFragment();
                title = getString(R.string.title_wallet);
                Log.d("LOGTAG", "Wallet");
                break;
            case 4:
                fragment = new AccountSettingsFragment();
                title = getString(R.string.title_account_settings);
                Log.d("LOGTAG", "Account Settings");
                break;
            case 5:
                fragment = new AboutUsFragment();
                title = getString(R.string.title_aboutus);
                Log.d("LOGTAG", "About Us");
                break;
            case 6:
                fragment = new ContactUsFragment();
                title = getString(R.string.title_contactus);
                Log.d("LOGTAG", "Contact Us");
                break;
            case 7:
                fragment = new LogOutFragment();
                title = getString(R.string.title_logout);
                Log.d("LOGTAG", "Log out");
                break;
            case 8:
                fragment = new SubCategoryFragment();
                title = getString(R.string.title_sub_categories);
                Log.d("LOGTAG", "Sub Categories");
                break;
            default:
                break;
        }

        if (fragment != null) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container_body, fragment);
            fragmentTransaction.commit();

            // set the toolbar title
            getSupportActionBar().setTitle(title);
        }
    }

    public void loadFragment(int id, Fragment fragment) {
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.replace(id, fragment, fragment.toString());
        ft.addToBackStack(null);
        ft.commit();
    }
}

public class SubCategoryFragment extends android.support.v4.app.Fragment {
    List<GetDataAdapter> GetDataAdapter1;
    RecyclerView recyclerView;
    RecyclerView.LayoutManager recyclerViewlayoutManager;
    RecyclerView.Adapter recyclerViewadapter;

    String GET_JSON_DATA_HTTP_URL;
    String JSON_IMAGE_TITLE_NAME = "image_title";
    String JSON_IMAGE_URL = "image_url";
    String JSON_IMAGE_ID = "id";

    JsonArrayRequest jsonArrayRequest ;
    RequestQueue requestQueue ;

    public SubCategoryFragment() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_sub_category, container, false);

        HomeActivity activity = new HomeActivity();
        activity.displayView(8); //Occuring error

        // Inflate the layout for this fragment
        return rootView;
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
    }

    @Override
    public void onDetach() {
        super.onDetach();
    }
}

以及
子类别fragment.java

public class HomeActivity extends AppCompatActivity implements FragmentDrawer.FragmentDrawerListener {
    private Toolbar mToolbar;
    private FragmentDrawer drawerFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        mToolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(mToolbar);
        getSupportActionBar().setDisplayShowHomeEnabled(true);
        drawerFragment = (FragmentDrawer)
                getSupportFragmentManager().findFragmentById(R.id.fragment_navigation_drawer);
        drawerFragment.setUp(R.id.fragment_navigation_drawer, (DrawerLayout) findViewById(R.id.drawer_layout), mToolbar);
        drawerFragment.setDrawerListener(this);

        displayView(0);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public void onDrawerItemSelected(View view, int position) {
        displayView(position);
    }

    public void displayView(int position) {
        Fragment fragment = null;
        String title = getString(R.string.app_name);
        switch (position) {
            case 0:
                fragment = new HomeFragment();
                title = getString(R.string.title_home);
                Log.d("LOGTAG", "Home");
                break;
            case 1:
                fragment = new CategoriesFragment();
                title = getString(R.string.title_categories);
                Log.d("LOGTAG", "Categories");
                break;
            case 2:
                fragment = new MyOrdersFragment();
                title = getString(R.string.title_myorders);
                Log.d("LOGTAG", "My Orders");
                break;
            case 3:
                fragment = new WalletFragment();
                title = getString(R.string.title_wallet);
                Log.d("LOGTAG", "Wallet");
                break;
            case 4:
                fragment = new AccountSettingsFragment();
                title = getString(R.string.title_account_settings);
                Log.d("LOGTAG", "Account Settings");
                break;
            case 5:
                fragment = new AboutUsFragment();
                title = getString(R.string.title_aboutus);
                Log.d("LOGTAG", "About Us");
                break;
            case 6:
                fragment = new ContactUsFragment();
                title = getString(R.string.title_contactus);
                Log.d("LOGTAG", "Contact Us");
                break;
            case 7:
                fragment = new LogOutFragment();
                title = getString(R.string.title_logout);
                Log.d("LOGTAG", "Log out");
                break;
            case 8:
                fragment = new SubCategoryFragment();
                title = getString(R.string.title_sub_categories);
                Log.d("LOGTAG", "Sub Categories");
                break;
            default:
                break;
        }

        if (fragment != null) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container_body, fragment);
            fragmentTransaction.commit();

            // set the toolbar title
            getSupportActionBar().setTitle(title);
        }
    }

    public void loadFragment(int id, Fragment fragment) {
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.replace(id, fragment, fragment.toString());
        ft.addToBackStack(null);
        ft.commit();
    }
}

public class SubCategoryFragment extends android.support.v4.app.Fragment {
    List<GetDataAdapter> GetDataAdapter1;
    RecyclerView recyclerView;
    RecyclerView.LayoutManager recyclerViewlayoutManager;
    RecyclerView.Adapter recyclerViewadapter;

    String GET_JSON_DATA_HTTP_URL;
    String JSON_IMAGE_TITLE_NAME = "image_title";
    String JSON_IMAGE_URL = "image_url";
    String JSON_IMAGE_ID = "id";

    JsonArrayRequest jsonArrayRequest ;
    RequestQueue requestQueue ;

    public SubCategoryFragment() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_sub_category, container, false);

        HomeActivity activity = new HomeActivity();
        activity.displayView(8); //Occuring error

        // Inflate the layout for this fragment
        return rootView;
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
    }

    @Override
    public void onDetach() {
        super.onDetach();
    }
}

公共类子类别Fragment扩展了android.support.v4.app.Fragment{
列出GetDataAdapter1；
回收视图回收视图；
RecyclerView.LayoutManager recyclerViewlayoutManager；
适配器RecycleWebAdapter；
字符串GET_JSON_DATA_HTTP_URL；
字符串JSON\u IMAGE\u TITLE\u NAME=“IMAGE\u TITLE”；
字符串JSON\u IMAGE\u URL=“IMAGE\u URL”；
字符串JSON_IMAGE_ID=“ID”；
JsonArrayRequest JsonArrayRequest；
请求队列请求队列；
公共子类别片段（）{
//必需的空公共构造函数
}
@凌驾
创建时的公共void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
}
@凌驾
创建视图上的公共视图（布局、充气机、视图组容器、，
Bundle savedInstanceState）{
视图根视图=充气机。充气（R.layout.fragment\u sub\u category，container，false）；
HomeActivity活动=新的HomeActivity（）；
activity.displayView（8）；//发生错误
//为该碎片膨胀布局
返回rootView；
}
@凌驾
公共事务主任（活动）{
超级转速计（活动）；
}
@凌驾
公共无效连接（）{
super.onDetach（）；
}
}

当我在子类别
Fragment
中添加
activity.displayView（8）
时，它显示错误

java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“android.content.res.Resources android.content.Context.getResources（）”

那么，如何更改
工具栏
文本？
您可以使用此选项

((AppCompatActivity)getActivity()).getSupportActionBar().setTitle("sub categories");

代替

 HomeActivity activity = new HomeActivity();
        activity.displayView(8); //Occuring error

你可以用这个

((AppCompatActivity)getActivity()).getSupportActionBar().setTitle("sub categories");

代替

 HomeActivity activity = new HomeActivity();
        activity.displayView(8); //Occuring error

您可以这样设置标题。
在子类别片段中：

工具栏工具栏

在oncreate视图（）中{

mtoolbar=（Toolbar）getActivity.findviewbyd（R.id.toolbarid）

设置支持工具栏（mtoolbar）：

}

然后在onActivityCreated（）中{

（（HomeActivity）getSupportCrionBar.settitle（“您的标题”）

}您可以这样设置标题。
在子类别片段中：

工具栏工具栏

在oncreate视图（）中{

mtoolbar=（Toolbar）getActivity.findviewbyd（R.id.toolbarid）

设置支持工具栏（mtoolbar）：

}

然后在onActivityCreated（）中{

（（HomeActivity）getSupportCrionBar.settitle（“您的标题”）

}
在Kotlin中，您可以使用以下功能：

(activity as AppCompatActivity).supportActionBar?.title = "Title here"

在Kotlin中，您可以使用以下各项：

(activity as AppCompatActivity).supportActionBar?.title = "Title here"

这就是不与父活动通信的方式
HomeActivity Activity=new HomeActivity（）；显示视图（8）//发生错误
您应该使用接口并将其附加到片段的附件中，但无论如何，为什么在onCreateView中您要尝试调用Activity方法？我的观点是，如果已经显示了片段，为什么要调用displayView Anyways，这是更改工具栏文本的另一种方法。这就是如何不与父活动通信
HomeActivity Activity=new HomeActivity（）；显示视图（8）//发生错误
您应该使用接口并将其附加到片段的附件中，但无论如何，为什么在onCreateView中您要尝试调用Activity方法？我的观点是，如果已经显示了片段，为什么要调用displayView呢？这是更改工具栏文本的另一种方法。