Android项目：换机报错

Question

所以我已经读完这本书了，Android Programming: The Big Nerd Ranch Guide，当我不得不改变时，我几乎完成了 CriminalIntent 应用程序从台式机到笔记本电脑。我刚刚复制了工作区并安装了 eclipse 和 SDK。现在 logcat 在尝试添加新罪行时给了我这个：

06-13 09:10:47.720: E/AndroidRuntime(535): java.lang.NullPointerException
06-13 09:10:47.720: E/AndroidRuntime(535):  at com.bignerdranch.android.criminalintent.CrimeFragment.onCreateView(CrimeFragment.java:102)
06-13 09:10:47.720: E/AndroidRuntime(535):  at android.support.v4.app.Fragment.performCreateView(Fragment.java:1789)
06-13 09:10:47.720: E/AndroidRuntime(535):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:955)
06-13 09:10:47.720: E/AndroidRuntime(535):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1138)
06-13 09:10:47.720: E/AndroidRuntime(535):  at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:740)
06-13 09:10:47.720: E/AndroidRuntime(535):  at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1501)
06-13 09:10:47.720: E/AndroidRuntime(535):  at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:490)
06-13 09:10:47.720: E/AndroidRuntime(535):  at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:163)
06-13 09:10:47.720: E/AndroidRuntime(535):  at android.support.v4.view.ViewPager.populate(ViewPager.java:1072)
06-13 09:10:47.720: E/AndroidRuntime(535):  at android.support.v4.view.ViewPager.populate(ViewPager.java:918)
06-13 09:10:47.720: E/AndroidRuntime(535):  at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1440)

CrimeFragment 的第 102 行是：

getActivity().getActionBar().setDisplayHomeAsUpEnabled(true);

也许新的支持库有一些不同？会很奇怪，我在一个月前做了我以前的设置。

另一件事是我首先安装了Android Studio和SDK，然后只是将eclipse指向那个SDK，也许这就是问题所在？ 该代码在旧机器上运行良好，所以我不会在此处发布，但如果您需要，我可以。

编辑：

@TargetApi(11)
public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState) {
    /* int resource, ViewGroup root, boolean attachToRoot */
    View v = inflater.inflate(R.layout.fragment_crime, parent, false);
    // enabling back button on menu bar to be shown
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
        /*
         * this action bar (guess back button in particular) is only compatible with holo.light
         * theme, maybe some others idk. There is a way around it but it is complicated, need to
         * use supportActionBar
         */
        if (NavUtils.getParentActivityName(getActivity()) != null) {
            getActivity().getActionBar().setDisplayHomeAsUpEnabled(true);
        }
    }

    mTitleField = (EditText) v.findViewById(R.id.crime_title);
    mTitleField.setText(mCrime.getTitle());
    mTitleField.addTextChangedListener(new TextWatcher() {
        public void onTextChanged(CharSequence c, int start, int before, int count) {
            mCrime.setTitle(c.toString());
        }

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {

        }

        @Override
        public void afterTextChanged(Editable s) {

        }
    });

    mDateButton = (Button) v.findViewById(R.id.crime_date);
    mDateButton.setOnClickListener(new View.OnClickListener() {
        /*
         * standard procedure of sending info between fragments of same activity - use
         * NewInstance
         */
        @Override
        public void onClick(View v) {
            FragmentManager fm = getActivity().getSupportFragmentManager();
            DatePickerFragment dialog = DatePickerFragment.newInstance(mCrime.getDate());
            /*
             * setting itself as a target to receive REQUEST_DATE after child is dead; first set
             * up REQUEST_DATE string; used together with private void sendResult(int
             * resultCode) and DialogInterface.onClickListener in positive button in
             * datePickerFragment, overriding onActivityResult is necessary in here
             */
            dialog.setTargetFragment(CrimeFragment.this, REQUEST_DATE);
            dialog.show(fm, DIALOG_DATE);
        }
    });

    mTimeButton = (Button) v.findViewById(R.id.crime_time);
    mTimeButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            FragmentManager fm = getActivity().getSupportFragmentManager();
            TimePickerFragment dialog = TimePickerFragment.newInstance(mCrime.getDate());
            dialog.setTargetFragment(CrimeFragment.this, REQUEST_TIME);
            dialog.show(fm, DIALOG_TIME);
        }
    });
    mDeleteButton = (Button) v.findViewById(R.id.crime_delete);
    mDeleteButton.setText(R.string.delete_crime);
    mDeleteButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            UUID crimeId = (UUID) getArguments().getSerializable(EXTRA_CRIME_ID);
            CrimeLab crimeLab = CrimeLab.get(getActivity());
            Crime crime = CrimeLab.get(getActivity()).getCrime(crimeId);
            crimeLab.deleteCrime(crime);
            crimeLab.saveCrimes();
            getActivity().finish();
        }
    });
    mPhotoButton = (ImageButton) v.findViewById(R.id.crime_imageButton);
    mPhotoButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent i = new Intent(getActivity(), CrimeCameraActivity.class);
            startActivity(i);
        }
    });
    // disabling camera button for devices without camera
    PackageManager pm = getActivity().getPackageManager();
    if (!pm.hasSystemFeature(PackageManager.FEATURE_CAMERA)
                    && !pm.hasSystemFeature(PackageManager.FEATURE_CAMERA_FRONT)) {
        mPhotoButton.setEnabled(false);
    }

    mSolvedCheckBox = (CheckBox) v.findViewById(R.id.crime_solved);
    mSolvedCheckBox.setChecked(mCrime.isSolved());
    mSolvedCheckBox.setOnCheckedChangeListener(new OnCheckedChangeListener() {
        public void onCheckedChanged(
                        /* checkButton needs compoundButton */CompoundButton buttonView,
                        boolean isChecked) {
            mCrime.setSolved(isChecked);
        }
    });
    updateDate();
    updateTime();
    return v;
}

Answer 1

它指出您的ActionBar 是null。如果您使用的是支持库 试试

getActivity().getSupportActionBar().setDisplayHomeAsUpEnabled(true);

而不是

getActivity().getActionBar().setDisplayHomeAsUpEnabled(true);