如何在不同的活动中更改不同风格的操作栏标题？

Question

我正在尝试用不同的标题更改我的2片段动作栏。但是，我得到变量'fragment'可能没有在这些行中初始化错误：

ProfileFragment fragment =（ProfileFragment）fragment.get（0）;

StartingTestFragment fragment2 =（StartingTestFragment）fragment2.get（0）;

在onPageSelected方法的CombineFragmentActivity中。感谢帮助。

CombineFragmentActivity.java

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.view.Gravity;

import java.util.ArrayList;
import java.util.List;
import java.util.Vector;

public class CombineFragmentActivity extends AppCompatActivity {
    private PagerAdapter mPagerAdapter;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.combine_fragment_activity);
        initialisePaging();
    }

    private void initialisePaging() {

        List<Fragment> fragments = new ArrayList<>();
        fragments.add(new StartingTestFragment());
        fragments.add(new ProfileFragment());
        mPagerAdapter = new PagerAdapter1(this.getSupportFragmentManager(),fragments);

        ViewPager pager = (ViewPager)findViewById(R.id.viewpager);
        pager.setAdapter(mPagerAdapter);

        pager.addOnPageChangeListener(new ViewPager.OnPageChangeListener(){
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                if(position == 0) {
                    ProfileFragment fragment = (ProfileFragment) fragment.get(0);
                    fragment.setActionBarTitle("Profil");
                } else {
                    StartingTestFragment fragment2 = (StartingTestFragment) fragment2.get(0);
                    fragment2.setActionBarTitle("Anasayfa");
                }

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }

        });
    }
}

ProfileFragment.java

import android.graphics.Color;
import android.graphics.Typeface;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.Toast;


public class ProfileFragment extends Fragment implements AdapterView.OnItemSelectedListener {
    public ProfileFragment() {
        // Required empty public constructor
    }


    public static ProfileFragment newInstance() {
        ProfileFragment fragment = new ProfileFragment();
        return fragment;
    }

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

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_profile, container, false);

    }

    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        Typeface ubuntu_MI = Typeface.createFromAsset(getActivity().getAssets(),"Ubuntu-MI.ttf");
        Typeface ubuntu_L = Typeface.createFromAsset(getActivity().getAssets(),"Ubuntu-L.ttf");
        Typeface ubuntu_R = Typeface.createFromAsset(getActivity().getAssets(),"Ubuntu-R.ttf");


        /**
         * Be carefull when trying to find a view element from a layout if the name is already defined in any layout
         * AndroidStudio will not hint an error and you will end up with with ugly null pointer error
        TextView question = (TextView) view.findViewById(R.id.textView7);
        question.setTypeface(ubuntu_R);
         TextView info = (TextView) view.findViewById(R.id.textView6);
         info.setTypeface(ubuntu_R);

         */


    }
    public void setActionBarTitle(String title) {
        Typeface ubuntu_MI = Typeface.createFromAsset(getActivity().getAssets(),"Ubuntu-MI.ttf");
        // Get the ActionBar
        android.support.v7.app.ActionBar ab = ((AppCompatActivity)getActivity()).getSupportActionBar();


        // Create a TextView programmatically.
        TextView tv = new TextView(getActivity());

        // Create a LayoutParams for TextView
        RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(
                RelativeLayout.LayoutParams.MATCH_PARENT, // Width of TextView
                RelativeLayout.LayoutParams.WRAP_CONTENT); // Height of TextView

        // Apply the layout parameters to TextView widget
        tv.setLayoutParams(lp);

        // Set text to display in TextView
        // This will set the ActionBar title text
        tv.setText(title);

        // Set the text color of TextView
        // This will change the ActionBar title text color
        tv.setTextColor(Color.parseColor("#FFF5EE"));

        // Center align the ActionBar title
        tv.setGravity(Gravity.CENTER_HORIZONTAL);

        // Set the serif font for TextView text
        // This will change ActionBar title text font
        tv.setTypeface(ubuntu_MI);

        // Underline the ActionBar title text
        // tv.setPaintFlags(tv.getPaintFlags()| Paint.UNDERLINE_TEXT_FLAG);

        // Set the ActionBar title font size
        tv.setTextSize(TypedValue.COMPLEX_UNIT_DIP,24);

        // Display a shadow around ActionBar title text
        //tv.setShadowLayer(
        //      1.f, // radius
        //    2.0f, // dx
        //  2.0f, // dy
        //  Color.parseColor("#FF8C00") // shadow color
        //);

        // Set the ActionBar display option
        ab.setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);

        // Finally, set the newly created TextView as ActionBar custom view
        ab.setCustomView(tv);
    }
    public boolean onOptionsItemSelected(MenuItem item) {
    //Action Bar' daki settings kısmına basıldığında ne yapacağını söylüyoruz.
        if(item.getItemId() == R.id.settings){
            Toast.makeText(getActivity(), "Ayarlara basıldı", Toast.LENGTH_SHORT).show();
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        super.onCreateOptionsMenu(menu, inflater);
        inflater.inflate(R.menu.menu_profile_activity, menu);

    }
    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) {

    }

}

StartingTestFragment.java

import android.graphics.Color;
import android.graphics.Typeface;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.RelativeLayout;
import android.widget.Spinner;
import android.widget.TextView;


public class StartingTestFragment extends Fragment implements AdapterView.OnItemSelectedListener {
    private Spinner spinner;
    ArrayAdapter<CharSequence> adapter;



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


    public static StartingTestFragment newInstance() {
        StartingTestFragment fragment = new StartingTestFragment();
        return fragment;
    }

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

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_startingtest, container, false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        spinner = (Spinner)view.findViewById(R.id.spinner);
        adapter = ArrayAdapter.createFromResource(getActivity(),R.array.simple_spinner_dropdown_item,R.layout.spinner_item);
        adapter.setDropDownViewResource(R.layout.spinner_dropdown_item);

        spinner.setAdapter(adapter);
        spinner.setOnItemSelectedListener(this);


        Typeface ubuntu_L = Typeface.createFromAsset(getActivity().getAssets(),"Ubuntu-L.ttf");
        Typeface ubuntu_R = Typeface.createFromAsset(getActivity().getAssets(),"Ubuntu-R.ttf");

        TextView info = (TextView) view.findViewById(R.id.textView6);
        TextView question = (TextView) view.findViewById(R.id.textView7);

        info.setTypeface(ubuntu_R);
        question.setTypeface(ubuntu_R);



    }
    public void setActionBarTitle(String title) {
        Typeface ubuntu_MI = Typeface.createFromAsset(getActivity().getAssets(),"Ubuntu-MI.ttf");
        // Get the ActionBar
        android.support.v7.app.ActionBar ab = ((AppCompatActivity)getActivity()).getSupportActionBar();


        // Create a TextView programmatically.
        TextView tv = new TextView(getActivity());

        // Create a LayoutParams for TextView
        RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(
                RelativeLayout.LayoutParams.MATCH_PARENT, // Width of TextView
                RelativeLayout.LayoutParams.WRAP_CONTENT); // Height of TextView

        // Apply the layout parameters to TextView widget
        tv.setLayoutParams(lp);

        // Set text to display in TextView
        // This will set the ActionBar title text
        tv.setText(title);

        // Set the text color of TextView
        // This will change the ActionBar title text color
        tv.setTextColor(Color.parseColor("#FFF5EE"));

        // Center align the ActionBar title
        tv.setGravity(Gravity.CENTER_HORIZONTAL);

        // Set the serif font for TextView text
        // This will change ActionBar title text font
        tv.setTypeface(ubuntu_MI);

        // Underline the ActionBar title text
        // tv.setPaintFlags(tv.getPaintFlags()| Paint.UNDERLINE_TEXT_FLAG);

        // Set the ActionBar title font size
        tv.setTextSize(TypedValue.COMPLEX_UNIT_DIP,24);

        // Display a shadow around ActionBar title text
        //tv.setShadowLayer(
        //      1.f, // radius
        //    2.0f, // dx
        //  2.0f, // dy
        //  Color.parseColor("#FF8C00") // shadow color
        //);

        // Set the ActionBar display option
        ab.setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);

        // Finally, set the newly created TextView as ActionBar custom view
        ab.setCustomView(tv);
    }

    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        switch (position) {
            case 0:
                // Whatever you want to happen when the first item gets selected
                break;
            case 1:
                // Whatever you want to happen when the second item gets selected
                break;
            case 2:
                // Whatever you want to happen when the thrid item gets selected
                break;

        }
    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) {

    }
}