NullPointerException onBackpressed（片段到活动）Android
每次使用actionbar上的后退按钮，从RouteView活动（使用片段）到RouteCose活动，我都会得到一个NullPointerException。问题是（我在这里得到的是null指针）OnCreate的routechose的以下值：NullPointerException onBackpressed（片段到活动）Android,android,android-intent,android-fragments,nullpointerexception,android-actionbar,Android,Android Intent,Android Fragments,Nullpointerexception,Android Actionbar,每次使用actionbar上的后退按钮，从RouteView活动（使用片段）到RouteCose活动，我都会得到一个NullPointerException。问题是（我在这里得到的是null指针）OnCreate的routechose的以下值： citySave = b.getInt("stadt"); 如果我使用actionbar（父活动）上的后退按钮，我不知道为什么会得到空指针，但如果我使用手机上的后退按钮，我不会得到空指针。如果我使用actionbar菜单项point，我也不会得到空指针
citySave = b.getInt("stadt");
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);
}
}
}
在以下部分中，您未按自己的意图传递任何值：
@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);
}
}
Intent route = new Intent(RouteView.this, RouteChooseActivity.class);
route .putExtra("stadt", citySave);
startActivity(route);
我添加了logcat，但不得不删除一些代码，因为有很多迹象……你对backbutton的理解有误，backbutton是手机上的back按钮，home按钮是actionbar上的按钮，通常返回navegation，第一个你得到的控制覆盖hook on Press backbutton，第二个是OnOptionsItemSelected，以android.R.id.home为例，很难理解您的解释。谢谢，但示例代码是什么样子的-我在谷歌找到了一些东西，但直到现在它才起作用：谢谢，我添加了一个bundle:bundle b=new bundle（）；b、 putInt（“Statt”，citySave）；在案例R.id.action_路线，但我已经得到一个空指针。是的。示例：你能用一个示例来添加你的答案的编辑吗，一个工作代码应该是什么样子的。谢谢，但是在这种情况下，putInt方法无法解决-我认为一直都需要一个包，不是吗？你在使用eclipse吗？什么都没有发生。如果你的意思是ctrl o，我会在AndroidStudio上获得一个新窗口：选择要覆盖的方法，但putint不可用。
@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);
}
}
Intent route = new Intent(RouteView.this, RouteChooseActivity.class);
route .putExtra("stadt", citySave);
startActivity(route);