我正在制作的应用程序出现问题，一切似乎都正常，直到我开始收到一个错误，似乎是无中生有，我不相信我从它工作时改变了任何东西，但每次我打开 Activity 它给我一个 NullPointerException，这是它的 logcat。
09-13 18:29:54.951: E/AndroidRuntime(4407): FATAL EXCEPTION: main
09-13 18:29:54.951: E/AndroidRuntime(4407): Process: renseew.knowyourtime, PID: 4407
09-13 18:29:54.951: E/AndroidRuntime(4407): java.lang.NullPointerException
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.support.v13.app.FragmentCompatICS.setMenuVisibility(FragmentCompatICS.java:23)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.support.v13.app.FragmentCompat$ICSFragmentCompatImpl.setMenuVisibility(FragmentCompat.java:41)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.support.v13.app.FragmentCompat.setMenuVisibility(FragmentCompat.java:68)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.support.v13.app.FragmentStatePagerAdapter.instantiateItem(FragmentStatePagerAdapter.java:120)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:837)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.support.v4.view.ViewPager.populate(ViewPager.java:987)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1441)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.View.measure(View.java:16497)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:762)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.View.measure(View.java:16497)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.View.measure(View.java:16497)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
09-13 18:29:54.951: E/AndroidRuntime(4407): at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.View.measure(View.java:16497)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
09-13 18:29:54.951: E/AndroidRuntime(4407): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.View.measure(View.java:16497)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1916)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1113)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1295)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.Choreographer.doCallbacks(Choreographer.java:574)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.Choreographer.doFrame(Choreographer.java:544)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.os.Handler.handleCallback(Handler.java:733)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.os.Handler.dispatchMessage(Handler.java:95)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.os.Looper.loop(Looper.java:136)
09-13 18:29:54.951: E/AndroidRuntime(4407): at android.app.ActivityThread.main(ActivityThread.java:5017)
09-13 18:29:54.951: E/AndroidRuntime(4407): at java.lang.reflect.Method.invokeNative(Native Method)
09-13 18:29:54.951: E/AndroidRuntime(4407): at java.lang.reflect.Method.invoke(Method.java:515)
09-13 18:29:54.951: E/AndroidRuntime(4407): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
09-13 18:29:54.951: E/AndroidRuntime(4407): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
09-13 18:29:54.951: E/AndroidRuntime(4407): at dalvik.system.NativeStart.main(Native Method)
该 Activity 使用 FragmentStatePagerAdapter 动态地将选项卡从 fragment 添加到 Activity ， 我还尝试将 if(position < companies.size() -1) 更改为 if(position < companies.size()) 没有变化(第一个在我开始收到错误之前有效)这是 Activity 代码。
public class UserDetails extends BaseActivity implements ActionBar.TabListener {
CompanyPagerAdapter companyPagerAdapter;
ViewPager viewPager;
Cursor cursor;
SettingsDBAdapter settingsDBAdapter;
String companyName;
private List<String> companies = new ArrayList<String>();
ActionBar ab;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_user_details);
updateActionBarNavigation();
initialize();
setupTabs();
getCompanies();
getTabs();
}
private void initialize() {
if(ab != null)
ab.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
viewPager = (ViewPager) findViewById(R.id.UDviewpager);
ContentResolver settingsContent = this.getContentResolver();
cursor = settingsContent.query(KnowYourTimeContentProvider.CONTENT_URI_SETTINGS, null, null, null, null);
settingsDBAdapter = new SettingsDBAdapter(getApplicationContext());
if (cursor.getCount() == 0) {
settingsDBAdapter.settingsDBOpen();
settingsDBAdapter.setDefaultSettings();
}
}
private void setupTabs() {
companyPagerAdapter = new CompanyPagerAdapter(getFragmentManager());
viewPager.setAdapter(companyPagerAdapter);
viewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
@Override
public void onPageSelected(int position) {
if (ab != null) {
ab.setSelectedNavigationItem(position);
}
}
});
}
private void getTabs() {
for (int i = 0; i < companyPagerAdapter.getCount(); i++) {
if (ab != null) {
ab.addTab(ab.newTab()
.setText(companyPagerAdapter.getPageTitle(i))
.setTabListener(this));
}
}
}
private void getCompanies() {
cursor = settingsDBAdapter.getCompanies();
if (companies.size() != 0) {
for (int i = 0; i < companies.size(); i++) {
companyName = companies.get(i);
companies.add(companyName);
}
} else if (cursor.getCount() != 0) {
while (cursor.moveToNext()) {
companyName = cursor.getString(cursor.getColumnIndex("company"));
companies.add(companyName);
}
} else {
companyName = getString(R.string.company);
companies.add(companyName);
}
companyPagerAdapter.notifyDataSetChanged();
}
@Override
protected void onNavDrawerStateChanged(boolean isOpen, boolean isAnimating) {
super.onNavDrawerStateChanged(isOpen, isAnimating);
updateActionBarNavigation();
}
@Override
protected void onActionBarAutoShowOrHide(boolean shown) {
super.onActionBarAutoShowOrHide(shown);
}
private void updateActionBarNavigation() {
boolean show = !isNavDrawerOpen();
ab = getActionBar();
if (show && ab != null) {
ab.setDisplayShowCustomEnabled(true);
ab.setDisplayShowTitleEnabled(true);
ab.setDisplayUseLogoEnabled(false);
ab.setTitle(getString(R.string.title_user_details));
} else if (ab != null) {
ab.setDisplayShowCustomEnabled(false);
ab.setDisplayShowTitleEnabled(false);
ab.setDisplayUseLogoEnabled(true);
}
}
@Override
protected int getSelfNavDrawerItem() {
return NAVDRAWER_ITEM_USERDETAILS;
}
@Override
public void onTabSelected(ActionBar.Tab tab,
FragmentTransaction fragmentTransaction) {
viewPager.setCurrentItem(tab.getPosition());
companies.get(tab.getPosition());
}
@Override
public void onTabUnselected(ActionBar.Tab tab,
FragmentTransaction fragmentTransaction) {
}
@Override
public void onTabReselected(ActionBar.Tab tab,
FragmentTransaction fragmentTransaction) {
}
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.usersettings_menu, menu);
return true;
}
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
menu.clear();
menu.add(Menu.NONE, R.id.addCompany, Menu.NONE, getString(R.string.add) + " " + getString(R.string.company));
menu.add(Menu.NONE, R.id.removeCompany, Menu.NONE, getString(R.string.subtract) + " " + getString(R.string.company));
return super.onPrepareOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem menuItem) {
switch (menuItem.getItemId()) {
case R.id.addCompany:
companies.clear();
companyName = getString(R.string.company);
companies.add(companyName);
companyPagerAdapter.notifyDataSetChanged();
getTabs();
return true;
case R.id.removeCompany:
return true;
default:
return super.onOptionsItemSelected(menuItem);
}
}
public class CompanyPagerAdapter extends FragmentStatePagerAdapter {
public CompanyPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
while (position < companies.size() - 1) {
if (position < companies.size() - 1) {
position++;
return FragmentUserDetails.newInstance(companies.get(position));
}
}
return null;
}
@Override
public int getCount() {
return companies.size();
}
@Override
public CharSequence getPageTitle(int position) {
while (position < companies.size() - 1) {
if (position < companies.size() - 1) {
position++;
return companies.get(position);
}
}
return "";
}
}
}
这里是 Activity 打开的 fragment 的代码。
public class FragmentUserDetails extends Fragment implements AdapterView.OnItemClickListener, View.OnClickListener {
private BaseAdapter listAdapter;
private Cursor settingsCursor, companyCursor;
private String payrate, payperiod, weekstart, allowances, maritalstatus;
private String companyname;
private Switch cbMaritalStatus;
public EditText etCompanyName, etPayrate;
private Spinner sPayPeriod, sPeriodStart, sAllowances;
SettingsDBAdapter settingsDBAdapter;
static FragmentUserDetails newInstance(String title) {
FragmentUserDetails fragmentUserDetails = new FragmentUserDetails();
Bundle args = new Bundle();
args.putString("title", title);
fragmentUserDetails.setArguments(args);
return fragmentUserDetails;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_user_details, container, false);
initialization(view);
return view;
}
private void initialization(View view) {
etCompanyName = (EditText) view.findViewById(R.id.UDedittextCompany);
etPayrate = (EditText) view.findViewById(R.id.UDedittextPayrate);
sPayPeriod = (Spinner) view.findViewById(R.id.UDspinnerPayPeriod);
sPeriodStart = (Spinner) view.findViewById(R.id.UDspinnerPeriodStart);
sAllowances = (Spinner) view.findViewById(R.id.UDspinnerAllowances);
cbMaritalStatus = (Switch) view.findViewById(R.id.UDswitchMaritalStatus);
Button save = (Button) view.findViewById(R.id.UDbuttonSaveSettings);
save.setOnClickListener(this);
ContentResolver settingsContent = getActivity().getContentResolver();
settingsCursor = settingsContent.query(KnowYourTimeContentProvider.CONTENT_URI_SETTINGS, null, null, null, null);
settingsDBAdapter = new SettingsDBAdapter(getActivity().getApplicationContext());
companyname = getArguments().getString("title");
if (settingsCursor.getCount() != 0) {
while (settingsCursor.moveToNext()) {
companyCursor = settingsDBAdapter.fetchCompanyInfo(companyname);
}
if (companyCursor.getCount() != 0) {
while (companyCursor.moveToNext()) {
payrate = companyCursor.getString(companyCursor.getColumnIndex("payrate"));
payperiod = companyCursor.getString(companyCursor.getColumnIndex("payperiod"));
weekstart = companyCursor.getString(companyCursor.getColumnIndex("weekstart"));
allowances = companyCursor.getString(companyCursor.getColumnIndex("allowances"));
maritalstatus = companyCursor.getString(companyCursor.getColumnIndex("maritalstatus"));
}
} else {
payrate = "";
payperiod = getString(R.string.weekly);
weekstart = getString(R.string.sunday);
allowances = "0";
maritalstatus = getString(R.string.no);
}
} else {
companyname = getString(R.string.company);
}
etCompanyName.setText(companyname);
etPayrate.setText(payrate);
sPayPeriod.setSelection(getIndex(sPayPeriod, payperiod));
sPeriodStart.setSelection(getIndex(sPeriodStart, weekstart));
sAllowances.setSelection(getIndex(sAllowances, allowances));
if (maritalstatus.equals(getString(R.string.yes))) {
cbMaritalStatus.setChecked(true);
} else {
cbMaritalStatus.setChecked(false);
}
}
}
抱歉放了这么多代码，我只是不确定是什么导致了这个问题。在此先感谢您的帮助
更新:
所以错误似乎确实来自 getItem() 使用调试器。它运行一次就好了(这是有道理的，因为最初有 1 行)但是第二次是它导致崩溃的时候。我还将其中的代码更改为此
public Fragment getItem(int position) {
FragmentUserDetails fragment = null;
if (position < companies.size() - 1) {
fragment = FragmentUserDetails.newInstance(companies.get(position));
}
return fragment;
}
按照建议使其更简单。仍然得到同样的错误。再次感谢您的帮助
最佳答案
您对 getItem() 的实现看起来非常可疑。这可能与您当前的错误有关，也可能无关。让我们分析一下您当前的代码:
public Fragment getItem(int position) {
while (position < companies.size() - 1) {
if (position < companies.size() - 1) {
position++;
return FragmentUserDetails.newInstance(companies.get(position));
}
}
return null;
}
为了继续这个分析，我们需要定义先决条件:
companies包含 5 个String。确切的值无关紧要。position从 0 开始，值为2。
在这种特殊情况下，while 和 if 条件的计算结果都是 true，因此 position 递增我们立即返回 newInstance() 的值。
这表明了一些非常重要的事情:只要 while 条件为 true，if 条件也为 true ，我们将立即返回一个值。这完全不需要 while 循环。
现在我们看到这个实现是不正确的，让我们备份并检查我们想要完成的事情。主要思想是我们要为索引 位置 处的“公司”返回一个 Fragment。简单的实现非常简单:
public Fragment getItem(int position) {
return FragmentUserDetails.newInstance(companies.get(position));
}
理论上，position永远不应该在范围之外，但是如果你想保险起见，可以添加一个if语句来进行错误检查:
public Fragment getItem(int position) {
if (0 <= position && position < companies.size()) {
return FragmentUserDetails.newInstance(companies.get(position));
}
}
现在，如果您仍然没有得到预期的行为，则错误出在其他地方，我们将需要分析您代码的其他部分。
关于java - 使用 fragmentstatepageradapter 的 nullpointerexception，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25828860/