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약간의 saveInstanceState 문제가 있습니다.NullPointer 예외 인 스턴스 문자열을 인스턴스 상태로 저장 Android
하나의 활동은 인 텐트를 통해 문자열 값을 다른 활동으로 보내며 이는 환상적으로 작동합니다. 이제 두 번째 활동에서 하나의 행 항목을 선택하여 세 번째 활동으로 넘어갑니다. 그러나 두 번째 작업에 액션 바 BACK 버튼을 사용하면 NullPointerException이 발생합니다.
이유는 물론 첫 번째 활동의 의도 문자열을로드 할 수 없기 때문입니다. 그래서 두 번째 활동에서이 인 텐트 문자열 값을 인스턴스 상태로 저장하고이 값을 oncreate methode에서 다시 얻으려고했습니다. 나는 많이 googlet했습니다, 나는 많이 시도했습니다. 그러나 Nullpointer는 사라지지 않을 것입니다.
약간의 힌트가 있으면 좋을 것입니다.
은 첫째, 실제로 savedInstanceState를 사용하지 않은 : 두 번째 활동의
내 코드 : 내가 볼 수
package de.cityknight.app;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Gravity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class RouteChooseActivity extends ActionBarActivity implements OnItemClickListener {
String citySave;
String[] titelRoute;
String[] descRoute;
Integer[] bildRoute;
ListView listView;
List<RowItem> rowItems;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_route_choose);
Bundle b = getIntent().getExtras();
if (savedInstanceState != null) {
savedInstanceState.getString("stadt");
}
else {
b.getString("stadt");
}
TextView headingRoute = (TextView) findViewById(R.id.routeTitel);
headingRoute.setText(String.format(getResources().getString(R.string.route_text)) + " " + b.getString("stadt") + " aus:");
if (b.getString("stadt").equals("Passau")) {
titelRoute = new String[]{"Die Altstadt", "Universität", "Essen und Trinken"};
descRoute = new String[]{"Die Altstadt Passaus bietet viele Attraktion: Rathaus, Dom und die vielen kleinen Gassen.",
"Deutschlands schönster Campus.", "Kulinarische Köstlichkeiten in Passau"};
bildRoute = new Integer[]{R.drawable.augsburg, R.drawable.bamberg, R.drawable.passau};
} else if (b.getString("stadt").equals("Augsburg")) {
titelRoute = new String[]{"Augsburg1", "Augsburg2", "Augsburg3"};
descRoute = new String[]{"Bla bla", "Mehr Bla", "Blubb"};
bildRoute = new Integer[]{R.drawable.augsburg, R.drawable.bamberg, R.drawable.passau};
} else if (b.getString("stadt").equals("Bamberg")) {
titelRoute = new String[]{"Bamberg", "Bamberg2", "Bamberg3"};
descRoute = new String[]{"Bla bla", "Mehr Bla", "Blubb"};
bildRoute = new Integer[]{R.drawable.augsburg, R.drawable.bamberg, R.drawable.passau};
} 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();
}
}
try {
rowItems = new ArrayList<RowItem>();
for (int i = 0; i < titelRoute.length; i++) {
RowItem item = new RowItem(bildRoute[i], titelRoute[i], descRoute[i]);
rowItems.add(item);
}
Comparator<RowItem> sortRoutes = new Comparator<RowItem>() {
@Override
public int compare(RowItem rowItem1, RowItem rowItem2) {
return rowItem1.getTitle().compareTo(rowItem2.getTitle());
}
};
Collections.sort(rowItems, sortRoutes);
listView = (ListView) findViewById(R.id.listRoute);
CityListViewAdapter adapter = new CityListViewAdapter(this, R.layout.row_items, rowItems);
listView.setAdapter(adapter);
listView.setOnItemClickListener(this);
} catch (ArrayIndexOutOfBoundsException rowItems) {
Context context = getApplicationContext();
CharSequence text = getResources().getString(R.string.ressourcefailed);
int duration = Toast.LENGTH_LONG;
Toast toast = Toast.makeText(context, text, duration);
toast.setGravity(Gravity.BOTTOM | Gravity.CENTER_HORIZONTAL, 0, 0);
toast.show();
}
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Intent intent = new Intent();
intent.setClass(RouteChooseActivity.this, RouteView.class);
RowItem item = (RowItem) parent.getItemAtPosition(position);
Bundle b = new Bundle();
b.putString("route", item.getTitle().toString());
intent.putExtras(b);
startActivity(intent);
}
protected void onSaveInstanceState(Bundle savedInstanceState) {
Bundle b = getIntent().getExtras();
b.getString("stadt");
savedInstanceState.putString("stadt", citySave);
super.onSaveInstanceState(savedInstanceState);
}
@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
savedInstanceState.getString(citySave);
Log.i("debug", "saved data: " + citySave);
}
@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);
}
}
}