工具栏以编程方式创建的Viewpager返回null

Question

我正在通过代码以编程方式创建ViewPager，但在生成的活动中，我没有得到ToolBar。我在xml文件和代码中都设置了工具栏，但我的代码一直说工具栏为空。

工具栏显示在我的主活动中，其中包含我的列表片段。每当我点击列表项时，应用程序就会崩溃，列表项会打开viewpager中包含的片段....或者至少我认为它是这样的。我完全失去了，任何帮助都会很棒。

这是堆栈跟踪：

03-24 00:33:50.128  26423-26423/com.fisheradelakin.criminalintent E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.fisheradelakin.criminalintent, PID: 26423
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fisheradelakin.criminalintent/com.fisheradelakin.criminalintent.CrimePagerActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.support.v7.widget.Toolbar.getTitle()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
        at android.app.ActivityThread.access$800(ActivityThread.java:151)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5254)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.support.v7.widget.Toolbar.getTitle()' on a null object reference
        at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:95)
        at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:88)
        at android.support.v7.internal.app.ToolbarActionBar.<init>(ToolbarActionBar.java:82)
        at android.support.v7.app.ActionBarActivityDelegateBase.setSupportActionBar(ActionBarActivityDelegateBase.java:189)
        at android.support.v7.app.ActionBarActivity.setSupportActionBar(ActionBarActivity.java:92)
        at com.fisheradelakin.criminalintent.CrimePagerActivity.onCreate(CrimePagerActivity.java:31)
        at android.app.Activity.performCreate(Activity.java:5990)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
            at android.app.ActivityThread.access$800(ActivityThread.java:151)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5254)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

这是CrimePagerActivity.java

public class CrimePagerActivity extends ActionBarActivity {
    private ViewPager mViewPager;
    private ArrayList<Crime> mCrimes;

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

        // create content view programmatically
        mViewPager = new ViewPager(this);
        mViewPager.setId(R.id.viewPager);
        setContentView(mViewPager);

        Toolbar toolbar = (Toolbar)(findViewById(R.id.toolbar));

        setSupportActionBar(toolbar);
        getSupportActionBar().setHomeButtonEnabled(true);


        mCrimes = CrimeLab.get(this).getCrimes();

        FragmentManager fm = getSupportFragmentManager();
        mViewPager.setAdapter(new FragmentStatePagerAdapter(fm) {
            @Override
            public Fragment getItem(int position) {
                Crime crime = mCrimes.get(position);
                return CrimeFragment.newInstance(crime.getId());
            }

            @Override
            public int getCount() {
                return mCrimes.size();
            }
        });

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

            }

            @Override
            public void onPageSelected(int position) {
                Crime crime = mCrimes.get(position);
                if(crime.getTitle() != null) {
                    getSupportActionBar().setTitle(crime.getTitle());
                }
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });

        // set the current item of viewpager to the id of the crime selected rather than the first
        UUID crimeId = (UUID)getIntent().getSerializableExtra(CrimeFragment.EXTRA_CRIME_ID);
        for(int i = 0; i < mCrimes.size(); i++) {
            if(mCrimes.get(i).getId().equals(crimeId)) {
                mViewPager.setCurrentItem(i);
                break;
            }
        }
    }
}

我显示的片段的xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              >

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

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/crime_title_label"
        style="?android:listSeparatorTextViewStyle"/>

    <EditText
        android:id="@+id/crime_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/crime_title_hint"/>

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/crime_details_label"
        style="?android:listSeparatorTextViewStyle"/>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/crime_date"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"/>

    <CheckBox
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/crime_solved"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:text="@string/crime_solved_label"/>

</LinearLayout>

最后但并非最不重要的是，我的CrimeFragment.java类：

public class CrimeFragment extends Fragment {
    public static final String EXTRA_CRIME_ID = "com.fisheradelakin.android.criminalintent.crime_id";

    private Crime mCrime;
    private EditText mTitleField;
    private Button mDateButton;
    private CheckBox mSolvedCheckBox;

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

        UUID crimeId = (UUID) getArguments().getSerializable(EXTRA_CRIME_ID);

        mCrime = CrimeLab.get(getActivity()).getCrime(crimeId);
    }

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

        mTitleField = (EditText) v.findViewById(R.id.crime_title);
        mTitleField.setText(mCrime.getTitle());
        mTitleField.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                mCrime.setTitle(s.toString());
            }

            @Override
            public void afterTextChanged(Editable s) {

            }
        });

        mDateButton = (Button)v.findViewById(R.id.crime_date);
        SimpleDateFormat sdf = new SimpleDateFormat("EEEE, MMM F, yyyy", Locale.US);
        mDateButton.setText(sdf.format(mCrime.getDate()));
        mDateButton.setEnabled(false);

        mSolvedCheckBox = (CheckBox)v.findViewById(R.id.crime_solved);
        mSolvedCheckBox.setChecked(mCrime.isSolved());
        mSolvedCheckBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                // set the crime's solved property
                mCrime.setSolved(isChecked);
            }
        });

        return v;
    }

    public static CrimeFragment newInstance(UUID crimeId) {
        Bundle args = new Bundle();
        args.putSerializable(EXTRA_CRIME_ID, crimeId);

        CrimeFragment fragment = new CrimeFragment();
        fragment.setArguments(args);

        return fragment;
    }
}

ViewPager活动由我的列表片段调用，我已经包含了以下代码

public class CrimeListFragment extends ListFragment {

    private static final String TAG = "CrimeListFragment";

    private ArrayList<Crime> mCrimes;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getActivity().setTitle(R.string.crimes_title);
        mCrimes = CrimeLab.get(getActivity()).getCrimes();

        CrimeAdapter adapter = new CrimeAdapter(mCrimes);
        setListAdapter(adapter);
    }

    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        Crime c = ((CrimeAdapter)getListAdapter()).getItem(position);

        // start crime pager activity
        Intent i = new Intent(getActivity(), CrimePagerActivity.class);
        i.putExtra(CrimeFragment.EXTRA_CRIME_ID, c.getId());
        startActivity(i);
    }

    private class CrimeAdapter extends ArrayAdapter<Crime> {

        public CrimeAdapter(ArrayList<Crime> crimes) {
            super(getActivity(), 0, crimes);
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // if we weren't given a view, inflate one
            if(convertView == null) {
                convertView = getActivity().getLayoutInflater().inflate(R.layout.list_item_crime, null);
            }

            // configure the view for this crime
            Crime c = getItem(position);

            TextView titleTextView = (TextView) convertView.findViewById(R.id.crime_list_item_titleTextView);
            titleTextView.setText(c.getTitle());

            TextView dateTextView = (TextView) convertView.findViewById(R.id.crime_list_item_dateTextView);
            dateTextView.setText(c.getDate().toString());

            CheckBox solvedCheckBox = (CheckBox) convertView.findViewById(R.id.crime_list_item_solvedCheckBox);
            solvedCheckBox.setChecked(c.isSolved());

            return convertView;
        }
    }

    @Override
    public void onResume() {
        super.onResume();
        ((CrimeAdapter)getListAdapter()).notifyDataSetChanged();
    }
}

Answer 1

我明白了。我需要在片段中设置工具栏，而不是像我一样在viewpager活动中设置工具栏。