我是Android编程的新手。我有一个带有一些活动的应用程序和一个SplashActivity，这是一个开始。类似的问题已经被提出，但没有一个答案对我有帮助，例如在我的finish()中添加EinkaufsListe-Activity功能，甚至添加此方法
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
Intent intent = new Intent(this, MainActivity.class);
startActivity(intent);
super.onStop();
return true;
}
return super.onKeyDown(keyCode, event);
}
添加super.onStop().没有！
我的应用程序包含一些Activities和一个SplashActivity，这是一个起始版本。
当我在ShopList-Activity并按下＆＃34;后退按钮＆＃34;应用程序崩溃并说：
0-07 13:37:56.250: E/AndroidRuntime(1124): java.lang.RuntimeException: Unable to stop activity {de.abayev.theapp/de.abayev.theapp.EinkaufsListe}: java.lang.NullPointerException
10-07 13:37:56.250: E/AndroidRuntime(1124): at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:3188)
10-07 13:37:56.250: E/AndroidRuntime(1124): at android.app.ActivityThread.handleStopActivity(ActivityThread.java:3234)
10-07 13:37:56.250: E/AndroidRuntime(1124): at android.app.ActivityThread.access$1100(ActivityThread.java:135)
10-07 13:37:56.250: E/AndroidRuntime(1124): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1223)
10-07 13:37:56.250: E/AndroidRuntime(1124): at android.os.Handler.dispatchMessage(Handler.java:102)
10-07 13:37:56.250: E/AndroidRuntime(1124): at android.os.Looper.loop(Looper.java:136)
10-07 13:37:56.250: E/AndroidRuntime(1124): at android.app.ActivityThread.main(ActivityThread.java:5017)
10-07 13:37:56.250: E/AndroidRuntime(1124): at java.lang.reflect.Method.invokeNative(Native Method)
10-07 13:37:56.250: E/AndroidRuntime(1124): at java.lang.reflect.Method.invoke(Method.java:515)
10-07 13:37:56.250: E/AndroidRuntime(1124): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
10-07 13:37:56.250: E/AndroidRuntime(1124): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
10-07 13:37:56.250: E/AndroidRuntime(1124): at dalvik.system.NativeStart.main(Native Method)
10-07 13:37:56.250: E/AndroidRuntime(1124): Caused by: java.lang.NullPointerException
10-07 13:37:56.250: E/AndroidRuntime(1124): at android.app.Activity.performStop(Activity.java:5388)
10-07 13:37:56.250: E/AndroidRuntime(1124): at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:3185)
10-07 13:37:56.250: E/AndroidRuntime(1124): ... 11 more
这是我的清单：
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:label="@string/app_name"
android:theme="@android:style/Theme.NoTitleBar.Fullscreen"
android:name=".SplashActivity">
<intent-filter >
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:label="@string/app_name"
android:theme="@android:style/Theme.NoTitleBar.Fullscreen"
android:name=".EinkaufsListe">
<intent-filter >
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".MHD_Liste">
<intent-filter >
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<service android:name=".MyAlarmService"
android:enabled="true" />
<receiver android:name=".MyReceiver"/>
</application>
我真的像天一样搜索，没有任何帮助。 如果您需要更多代码，请告诉我。
修改 这是来自EinkaufsListe的OnCreate
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.einkaufsliste);
openDB();
eddit1 = (EditText) findViewById (R.id.edittxt1);
eddit1.setOnKeyListener(OnKey);
LV = (ListView) findViewById (R.id.liVi1);
registerForContextMenu(LV);
startManagingCursor(cursor_main);
update_list();
LV.setAdapter(cur_adapter);
Intent myIntent = new Intent(EinkaufsListe.this, MyReceiver.class);
pendingIntent = PendingIntent.getBroadcast(EinkaufsListe.this, 0, myIntent,0);
} // OnCreate
编辑2：
好的我不知道哪些代码更相关，所以我只是发布了整个课程的其余部分：
// Methode für das Eingabefeld mit übergabe an DB
public OnKeyListener OnKey = new OnKeyListener ()
{
@Override
public boolean onKey(View v, int keyCode, KeyEvent event)
{
if ((event.getAction() == KeyEvent.ACTION_DOWN) && (keyCode == KeyEvent.KEYCODE_ENTER))
{
String writtenText = eddit1.getText().toString();
if( writtenText.indexOf(",") != -1 )
{
String a;
String b;
a = writtenText.substring( 0, writtenText.indexOf(",") );
b = writtenText.substring( writtenText.indexOf(",")+1, writtenText.length() ); // writtenText.indexOf(",")+1 um Abschnitt nach dem Komma zu beginnen
myDb.insertRow(a,b,null,EinkaufTabelle); //neue Zeile in DB anfügen
eddit1.setText("");
update_list();
}
else
{
myDb.insertRow(writtenText," ohne Produktart ",null,EinkaufTabelle); //neue Zeile in DB anfügen
eddit1.setText("");
update_list();
}
}
return false;
} // OnKey
}; // OnKeyListener
////////////////////////////////////////////__Datenbank-Methoden__/////////////////////////////////////////
@Override
protected void onDestroy() {
super.onDestroy();
if(null != myDb)
closeDB();
}
private void openDB() {
myDb = new DBAdapter(this);
myDb.open();
}
private void closeDB() {
myDb.close();
}
public DBAdapter getDB()
{
DBAdapter angefragte_DB = myDb;
return angefragte_DB;
}
/////////////////////////////////////////////__ListView Methoden__/////////////////////////////////////////
public void onToggleClicked(View view)
{
boolean on = ((ToggleButton) view).isChecked();
if (on)
{ checked = true; update_list(); }
else
{ checked = false; update_list(); }
} // onToggleClicked, nach dem Beispiel von developer.Android.com
protected void update_list()
{
if (checked == true)
cursor_main = myDb.orderRows(EinkaufTabelle);
else
cursor_main = myDb.getAllRows(EinkaufTabelle);
//startManagingCursor(cursor);
final String[] anzeigeSpalten = new String[]{ "name", "productType"};
final int[] anzeigeViews = new int[] { R.id.dataLV_tv, R.id.dataLV_tv2 };
cur_adapter = new SimpleCursorAdapter(this, R.layout.datensaetze_listview, cursor_main, anzeigeSpalten, anzeigeViews);
LV.setAdapter(cur_adapter);
} // update_list
//Contextmenu anlegen
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo)
{
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.context_menu, menu);
}; // OnCreateContextMenu
//
public boolean onContextItemSelected(MenuItem item)
{
AdapterContextMenuInfo menuInfo = (AdapterContextMenuInfo) item.getMenuInfo();
int rowId;
cursor_main = cur_adapter.getCursor();
cursor_main.moveToPosition(menuInfo.position);
rowId = cursor_main.getInt(cursor_main.getColumnIndex("_id"));
itemId = cursor_main.getInt(cursor_main.getColumnIndex("_id"));
switch (item.getItemId())
{
case R.id.loeschen : myDb.deleteRow(rowId, EinkaufTabelle); break;
case R.id.mhd : showDialog(MHD_DIALOG);
break;
default: break;
}
update_list();
return true;
} // onContextItemSelected
/////////////////////////////////////////////__Dialog Methoden__/////////////////////////////////////////
protected Dialog onCreateDialog(int num)
{ Dialog rückgabe = null;
switch(num)
{
case MHD_DIALOG: rückgabe = zeigeMHDDialog();
break;
default : break;
}
return rückgabe;
} // onCreateDialog
private DatePickerDialog zeigeMHDDialog()
{
final DatePickerDialog.OnDateSetListener datelistener;
datelistener = new DatePickerDialog.OnDateSetListener() {
public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) // wird wegen des CallBack Meachanismus erst beim Schließen,
{ // des DatePickerDialogs aufgerufen
int Tag = dayOfMonth;
int Monat = monthOfYear;
int Jahr = year;
String ablaufsDat;
//switch-Anweisung falls Tag < 7 muss Benutzter trotzdem richtig gewarnt werden
switch(dayOfMonth)
{
case 7: Tag = 30; Monat = monthOfYear - 1; break;
case 6: Tag = 29; Monat = monthOfYear - 1; break;
case 5: Tag = 28; Monat = monthOfYear - 1; break;
case 4: Tag = 27; Monat = monthOfYear - 1; break;
case 3: Tag = 26; Monat = monthOfYear - 1; break;
case 2: Tag = 25; Monat = monthOfYear - 1; break;
case 1: Tag = 24; Monat = monthOfYear - 1; break;
default: Tag = dayOfMonth - 7; Monat = monthOfYear; Jahr = year; break;
}
if(monthOfYear == 0) // per Definition gehen die Monate im PC von 0 - 11
{
switch(dayOfMonth)
{
case 7: Tag = 30; Monat = 11; Jahr = year - 1; break;
case 6: Tag = 29; Monat = 11; Jahr = year - 1; break;
case 5: Tag = 28; Monat = 11; Jahr = year - 1; break;
case 4: Tag = 27; Monat = 11; Jahr = year - 1; break;
case 3: Tag = 26; Monat = 11; Jahr = year - 1; break;
case 2: Tag = 25; Monat = 11; Jahr = year - 1; break;
case 1: Tag = 24; Monat = 11; Jahr = year - 1; break;
default: Tag = dayOfMonth - 7; Monat = monthOfYear; Jahr = year; break;
}
}
String name = cursor_main.getString(cursor_main.getColumnIndex("name"));
String productType = cursor_main.getString(cursor_main.getColumnIndex("productType"));
neuesDat = Tag + "." + (Monat +1) + "." + Jahr ;
ablaufsDat = dayOfMonth + "." + (monthOfYear +1) + "." + year ;
myDb.updateRowDate(itemId, ablaufsDat);
myDb.insertRow(name, productType, ablaufsDat, MHD_Tabelle); // in die MHD Tabelle einfügen
Toast.makeText(getApplicationContext(), "Mindesthaltbarkeitsdatum wurde eingestellt. Sie können es in der Liste für die aufzubewahrenden Produkte einsehen", Toast.LENGTH_LONG).show();
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.YEAR, Jahr);
calendar.set(Calendar.MONTH, Monat);
calendar.set(Calendar.DAY_OF_MONTH, Tag);
AlarmManager alarmManager = (AlarmManager)getSystemService(ALARM_SERVICE);
alarmManager.set(AlarmManager.RTC, calendar.getTimeInMillis(), pendingIntent);
} //onDateSet
}; //datelistener
// Dialog erzeugen und Datum auf heute setzen
Calendar c = Calendar.getInstance();
int J = c.get(Calendar.YEAR);
int M = c.get(Calendar.MONTH);
int T = c.get(Calendar.DAY_OF_MONTH);
DatePickerDialog dialog = new DatePickerDialog (this, datelistener, J, M, T);
return dialog;
}
// methode für den back Button
@Override
public void onBackPressed() {
Intent intent_x = new Intent(this, MainActivity.class);
startActivity(intent_x);
finish();
}
} // end of class
这里是清洁后的痕迹：
10-07 15:00:24.100: E/AndroidRuntime(1435): FATAL EXCEPTION: main
10-07 15:00:24.100: E/AndroidRuntime(1435): Process: de.abayev.theshapp, PID: 1435
10-07 15:00:24.100: E/AndroidRuntime(1435): java.lang.RuntimeException: Unable to stop activity {de.abayev.theshapp/de.abayev.theshapp.EinkaufsListe}: java.lang.NullPointerException
10-07 15:00:24.100: E/AndroidRuntime(1435): at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3461)
10-07 15:00:24.100: E/AndroidRuntime(1435): at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3515)
10-07 15:00:24.100: E/AndroidRuntime(1435): at android.app.ActivityThread.access$1400(ActivityThread.java:135)
10-07 15:00:24.100: E/AndroidRuntime(1435): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1249)
10-07 15:00:24.100: E/AndroidRuntime(1435): at android.os.Handler.dispatchMessage(Handler.java:102)
10-07 15:00:24.100: E/AndroidRuntime(1435): at android.os.Looper.loop(Looper.java:136)
10-07 15:00:24.100: E/AndroidRuntime(1435): at android.app.ActivityThread.main(ActivityThread.java:5017)
10-07 15:00:24.100: E/AndroidRuntime(1435): at java.lang.reflect.Method.invokeNative(Native Method)
10-07 15:00:24.100: E/AndroidRuntime(1435): at java.lang.reflect.Method.invoke(Method.java:515)
10-07 15:00:24.100: E/AndroidRuntime(1435): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
10-07 15:00:24.100: E/AndroidRuntime(1435): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
10-07 15:00:24.100: E/AndroidRuntime(1435): at dalvik.system.NativeStart.main(Native Method)
10-07 15:00:24.100: E/AndroidRuntime(1435): Caused by: java.lang.NullPointerException
10-07 15:00:24.100: E/AndroidRuntime(1435): at android.app.Activity.performStop(Activity.java:5388)
10-07 15:00:24.100: E/AndroidRuntime(1435): at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3456)
10-07 15:00:24.100: E/AndroidRuntime(1435): ... 11 more
答案 0 :(得分：2)
super.onStop();
致电finish()以结束活动。
答案 1 :(得分：0)
使用此代替onKeyDown：
@Override
public void onBackPressed() {
Intent intent = new Intent(this, MainActivity.class);
startActivity(intent);
finish();
}
答案 2 :(得分：0)
在super.onStop()以外的任何地方致电onStop()是错误的，但不会导致异常。
你的问题
Caused by: java.lang.NullPointerException
at android.app.Activity.performStop(Activity.java:5388)
是由于您向null Cursor提供了startManagingCursor() onCreate()，特别是startManagingCursor(cursor_main);
：
cursor_main其中startManagingCursor()尚未初始化。
完全删除{{1}}。无论如何，你不应该将它用于新代码。