每次我使用RouteView Activity（使用片段）到RouteChoose Activity的操作栏上的后退按钮时，我都会收到NullPointerException。问题 - 我得到Nullpointer - 是OnCreate的RouteChoose的以下值：
citySave = b.getInt("stadt");
我不知道为什么我会得到一个Nullpointer，如果我在动作栏上使用后退按钮（父活动），但是如果我使用手机上的后退按钮，我就没有Nullpointer。如果我使用操作栏菜单项目点，我也没有NullPointer。如何在操作栏上调用左侧的小后箭来发送意图？
P.S。：如果有人提示，如何简化if else条件以防止冗余代码，欢迎您：）
RouteChoose：
public class RouteChooseActivity extends ActionBarActivity implements OnItemClickListener {
Integer citySave;
Integer routeSave;
String cityTitle;
ListView listView;
List<RowItem> cities;
CityParser parser = new CityParser();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_route_choose);
Bundle b = getIntent().getExtras();
citySave = b.getInt("stadt");
cityTitle = b.getString("titel_stadt");
TextView headingRoute = (TextView) findViewById(R.id.routeTitel);
headingRoute.setText(String.format(getResources().getString(R.string.route_text)) + " " + cityTitle + " aus:");
listView = (ListView) findViewById(R.id.listRoute);
if (citySave.equals(1)) {
try {
cities = parser.parse(getAssets().open("route_passau.xml"));
CityListViewAdapter adapter = new CityListViewAdapter(this, R.layout.row_items, (ArrayList<RowItem>) cities);
Collections.sort(cities, new Comparator<RowItem>() {
public int compare(RowItem s1, RowItem s2) {
return s1.getTitle().compareTo(s2.getTitle());
}
});
listView.setAdapter(adapter);
} catch (IOException e) {
e.printStackTrace();
}
} else if (citySave.equals(2)) {
try {
cities = parser.parse(getAssets().open("route_bamberg.xml"));
CityListViewAdapter adapter = new CityListViewAdapter(this, R.layout.row_items, (ArrayList<RowItem>) cities);
Collections.sort(cities, new Comparator<RowItem>() {
public int compare(RowItem s1, RowItem s2) {
return s1.getTitle().compareTo(s2.getTitle());
}
});
listView.setAdapter(adapter);
} catch (IOException e) {
e.printStackTrace();
}
} else if (citySave.equals(3)) {
try {
cities = parser.parse(getAssets().open("route_augsburg.xml"));
CityListViewAdapter adapter = new CityListViewAdapter(this, R.layout.row_items, (ArrayList<RowItem>) cities);
Collections.sort(cities, new Comparator<RowItem>() {
public int compare(RowItem s1, RowItem s2) {
return s1.getTitle().compareTo(s2.getTitle());
}
});
listView.setAdapter(adapter);
} catch (IOException e) {
e.printStackTrace();
}
} else {
try {
TextView errorMessage = (TextView) findViewById(R.id.routeTitel);
errorMessage.setText(R.string.errorroute);
} catch (NullPointerException e) {
Context context = getApplicationContext();
CharSequence text = getResources().getString(R.string.errorroute);
int duration = Toast.LENGTH_LONG;
Toast toast = Toast.makeText(context, text, duration);
toast.setGravity(Gravity.BOTTOM | Gravity.CENTER_HORIZONTAL, 0, 0);
toast.show();
}
}
listView.setOnItemClickListener(this);
final ActionBar actionBar = getSupportActionBar();
setTitle("Routen in" + " " + cityTitle);
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Intent intent = new Intent();
intent.setClass(RouteChooseActivity.this, RouteView.class);
RowItem cities = (RowItem) parent.getItemAtPosition(position);
Bundle b = new Bundle();
b.putInt("stadt", citySave);
b.putString("titel_stadt", cityTitle);
b.putInt("route", cities.getID());
b.putString("titel_route", cities.getTitle());
intent.putExtras(b);
startActivity(intent);
}
@Override
protected void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
Bundle b = getIntent().getExtras();
citySave = b.getInt("stadt");
cityTitle = b.getString("titel_stadt");
savedInstanceState.putInt("stadt", citySave);
}
@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
citySave = savedInstanceState.getInt("stadt");
Log.i("debug", "saved data: " + citySave);
}
@Override
public void onResume() {
super.onResume();
Bundle b = getIntent().getExtras();
citySave = b.getInt("stadt");
cityTitle = b.getString("titel_stadt");
}
@Override
public void onPause() {
super.onPause();
Bundle b = new Bundle();
b.putInt("stadt", citySave);
b.putString("titel_stadt", cityTitle);
unbindDrawables(findViewById(R.id.Bild));
System.gc();
}
@Override
public void onStop() {
super.onStop();
Bundle b = new Bundle();
b.putInt("stadt", citySave);
b.putString("titel_stadt", cityTitle);
finish();
}
@Override
protected void onDestroy()
{
super.onDestroy();
unbindDrawables(findViewById(R.id.Bild));
System.gc();
}
@Override
public void onRestart() {
super.onRestart();
Bundle b = getIntent().getExtras();
citySave = b.getInt("stadt");
cityTitle = b.getString("titel_stadt");
}
private void unbindDrawables(View view)
{
if (view.getBackground() != null)
{
view.getBackground().setCallback(null);
}
if (view instanceof ViewGroup && !(view instanceof AdapterView))
{
for (int i = 0; i < ((ViewGroup) view).getChildCount(); i++)
{
unbindDrawables(((ViewGroup) view).getChildAt(i));
}
((ViewGroup) view).removeAllViews();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.route, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
switch (item.getItemId()) {
case R.id.action_stadt:
setContentView(R.layout.activity_stadt);
Intent stadt = new Intent(RouteChooseActivity.this, StadtActivity.class);
startActivity(stadt);
return true;
case R.id.action_help:
setContentView(R.layout.activity_help);
Intent help = new Intent(RouteChooseActivity.this, Help.class);
startActivity(help);
return true;
case R.id.action_exit:
moveTaskToBack(true);
System.exit(0);
return true;
default:
return super.onOptionsItemSelected(item);
}
}
}
RouteView：
public class RouteView extends ActionBarActivity implements ActionBar.TabListener {
/**
* The {@link android.support.v4.view.PagerAdapter} that will provide
* fragments for each of the sections. We use a
* {@link FragmentPagerAdapter} derivative, which will keep every
* loaded fragment in memory. If this becomes too memory intensive, it
* may be best to switch to a
* {@link android.support.v4.app.FragmentStatePagerAdapter}.
*
*/
Integer citySave;
String cityTitle;
Integer routeSave;
String routeTitel;
private static int NUM_ITEMS = 2;
SectionsPagerAdapter mSectionsPagerAdapter;
ListView listView;
ArrayList<RowItem> pois;
/**
* The {@link ViewPager} that will host the section contents.
*/
ViewPager mViewPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_route_view);
Bundle b = getIntent().getExtras();
citySave = b.getInt("stadt");
cityTitle = b.getString("titel_stadt");
routeSave = b.getInt("route");
routeTitel = b.getString("titel_route");
b.putString("titel_route",routeTitel);
b.putInt("route", routeSave);
//RouteItemFragment fragobj = new RouteItemFragment();
//fragobj.setArguments(b);
// Set up the action bar.
final ActionBar actionBar = getSupportActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
setTitle("Route:" + " " + routeTitel);
// Create the adapter that will return a fragment for each of the three
// primary sections of the activity.
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mSectionsPagerAdapter);
// When swiping between different sections, select the corresponding
// tab. We can also use ActionBar.Tab#select() to do this if we have
// a reference to the Tab.
mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
@Override
public void onPageSelected(int position) {
actionBar.setSelectedNavigationItem(position);
}
});
// For each of the sections in the app, add a tab to the action bar.
for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
// Create a tab with text corresponding to the page title defined by
// the adapter. Also specify this Activity object, which implements
// the TabListener interface, as the callback (listener) for when
// this tab is selected.
actionBar.addTab(
actionBar.newTab()
.setText(mSectionsPagerAdapter.getPageTitle(i))
.setTabListener(this));
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.route_view, menu);
return true;
}
@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
// When the given tab is selected, switch to the corresponding page in
// the ViewPager.
mViewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}
@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a PlaceholderFragment (defined as a static inner class below).
switch (position){
case 0:
return RouteItemFragment.newInstance(position);
case 1:
return MapFragment.newInstance(position);
default:
return PlaceholderFragment.newInstance(position);
}
}
@Override
public int getCount() {
// Show 2 total pages.
return NUM_ITEMS;
}
@Override
public CharSequence getPageTitle(int position) {
Locale l = Locale.getDefault();
switch (position) {
case 0:
return getString(R.string.title_section1).toUpperCase(l);
case 1:
return getString(R.string.title_section2).toUpperCase(l);
}
return null;
}
}
public static class RouteItemFragment extends ListFragment implements AdapterView.OnItemClickListener {
private static final String ARG_SECTION_NUMBER = "section_number";
ListView listView;
List<RowItem> pois;
Integer routeSave;
String routeTitel;
private View rootView;
public static RouteItemFragment newInstance(int sectionNumber) {
RouteItemFragment fragment = new RouteItemFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public RouteItemFragment() {
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
routeSave = getActivity().getIntent().getExtras().getInt("route");
routeTitel = getActivity().getIntent().getStringExtra("titel_route");
//pois = getActivity().getIntent().getParcelableArrayListExtra("pois");
if (routeSave.equals(1)) {
try {
PoiParser parser = new PoiParser();
pois = parser.parse(getActivity().getAssets().open("poi_passau1.xml"));
CityListViewAdapter adapter = new CityListViewAdapter(getActivity(), R.layout.row_items, pois);
listView.setAdapter(adapter);
Collections.sort(pois, new Comparator<RowItem>() {
public int compare(RowItem s1, RowItem s2) {
return s1.getID() - s2.getID();
}
});
} catch (IOException e) {
e.printStackTrace();
}
} else if (routeSave.equals(2)){
try {
PoiParser parser = new PoiParser();
pois = parser.parse(getActivity().getAssets().open("poi_passau1.xml"));
CityListViewAdapter adapter = new CityListViewAdapter(getActivity(), R.layout.row_items, pois);
listView.setAdapter(adapter);
Collections.sort(pois, new Comparator<RowItem>() {
public int compare(RowItem s1, RowItem s2) {
return s1.getID() - s2.getID();
}
});
} catch (IOException e) {
e.printStackTrace();
}
} else if (routeSave.equals(7)){
try {
PoiParser parser = new PoiParser();
pois = parser.parse(getActivity().getAssets().open("poi_passau1.xml"));
CityListViewAdapter adapter = new CityListViewAdapter(getActivity(), R.layout.row_items, pois);
listView.setAdapter(adapter);
Collections.sort(pois, new Comparator<RowItem>() {
public int compare(RowItem s1, RowItem s2) {
return s1.getID() - s2.getID();
}
});
} catch (IOException e) {
e.printStackTrace();
}
} else if (routeSave.equals(8)){
try {
PoiParser parser = new PoiParser();
pois = parser.parse(getActivity().getAssets().open("poi_passau1.xml"));
CityListViewAdapter adapter = new CityListViewAdapter(getActivity(), R.layout.row_items, pois);
listView.setAdapter(adapter);
Collections.sort(pois, new Comparator<RowItem>() {
public int compare(RowItem s1, RowItem s2) {
return s1.getID() - s2.getID();
}
});
} catch (IOException e) {
e.printStackTrace();
}
} else if (routeSave.equals(9)){
try {
PoiParser parser = new PoiParser();
pois = parser.parse(getActivity().getAssets().open("poi_passau1.xml"));
CityListViewAdapter adapter = new CityListViewAdapter(getActivity(), R.layout.row_items, pois);
listView.setAdapter(adapter);
Collections.sort(pois, new Comparator<RowItem>() {
public int compare(RowItem s1, RowItem s2) {
return s1.getID() - s2.getID();
}
});
} catch (IOException e) {
e.printStackTrace();
}
} else {
try {
TextView textView = (TextView) getView().findViewById(R.id.textRouteitem);
textView.setText(String.format(getResources().getString(R.string.errorroute)));
} catch (NullPointerException e) {
Context context = getActivity().getApplicationContext();
CharSequence text = getResources().getString(R.string.errorroute);
int duration = Toast.LENGTH_LONG;
Toast toast = Toast.makeText(context, text, duration);
toast.setGravity(Gravity.BOTTOM | Gravity.CENTER_HORIZONTAL, 0, 0);
toast.show();
}
}
Bundle b = new Bundle();
b.putParcelableArrayList("pois", (ArrayList<? extends android.os.Parcelable>) pois);
listView.setOnItemClickListener(this);
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
}
@Override
public void onDestroyView() {
super.onDestroyView();
rootView = null; // now cleaning up!
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.fragment_route_item, container, false);
TextView textView = (TextView) rootView.findViewById(R.id.textRouteitem);
listView = (ListView) rootView.findViewById(android.R.id.list);
textView.setText(String.format(getResources().getString(R.string.routeViewfragment)) + " "
+ getActivity().getIntent().getStringExtra("titel_route"));
return rootView;
}
@Override
public void onItemClick(AdapterView<?> adapterView, View parent, int position, long l) {
Intent intent = new Intent();
intent.setClass(getActivity(), PoiView.class);
RowItem pois = (RowItem) getListView().getItemAtPosition(position);
Bundle b = new Bundle();
b.putInt("stadt", pois.getID());
b.putParcelableArrayList("pois", pois);
intent.putExtras(b);
startActivity(intent);
}
}
public void onBackPressed() {
super.onBackPressed();
Intent intent = new Intent();
intent.setClass(RouteView.this, RouteChooseActivity.class);
Bundle b = new Bundle();
b.putInt("stadt", citySave);
b.putString("titel_stadt", cityTitle);
intent.putExtras(b);
startActivity(intent);
finish();
}
public void onPause() {
super.onPause();
Bundle b = new Bundle();
b.putInt("stadt", citySave);
b.putInt("route", routeSave);
b.putString("route_titel",routeTitel);
finish();
}
public void onResume() {
super.onResume();
Bundle b = getIntent().getExtras();
citySave = b.getInt("stadt");
routeSave = b.getInt("route");
routeTitel = b.getString("route_titel");
}
public void onStop() {
super.onStop();
finish();
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.action_stadt:
setContentView(R.layout.activity_stadt);
Intent stadt = new Intent(RouteView.this, StadtActivity.class);
startActivity(stadt);
return true;
case R.id.action_route:
setContentView(R.layout.activity_route_choose);
Intent route = new Intent(RouteView.this, RouteChooseActivity.class);
Bundle b = new Bundle();
route.putExtra("stadt", citySave);
route.putExtra("stadt_titel", cityTitle);
startActivity(route);
return true;
case R.id.action_help:
setContentView(R.layout.activity_help);
Intent help = new Intent(RouteView.this, Help.class);
startActivity(help);
return true;
case R.id.action_exit:
moveTaskToBack(true);
System.exit(0);
return true;
default:
return super.onOptionsItemSelected(item);
}
}
}
logcat的
java.lang.RuntimeException: Unable to start activity ComponentInfo{de.cityknight.app/de.cityknight.app.RouteChooseActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at de.cityknight.app.RouteChooseActivity.onCreate(RouteChooseActivity.java:44)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：1)
你没有在这些部分中传递任何值：
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.action_stadt:
Intent stadt = new Intent(RouteView.this, StadtActivity.class);
startActivity(stadt);
return true;
case R.id.action_route:
setContentView(R.layout.activity_route_choose);
Intent route = new Intent(RouteView.this, RouteChooseActivity.class);
startActivity(route);
return true;
case R.id.action_help:
setContentView(R.layout.activity_help);
Intent help = new Intent(RouteView.this, Help.class);
startActivity(help);
return true;
case R.id.action_exit:
moveTaskToBack(true);
System.exit(0);
return true;
default:
return super.onOptionsItemSelected(item);
}
}
你必须做这样的事情：
Intent route = new Intent(RouteView.this, RouteChooseActivity.class);
route .putExtra("stadt", citySave);
startActivity(route);