如何将字符串存储在我在私有异步类中生成的共享首选项中，然后在另一个活动中使用它？
public class Login extends ActionBarActivity implements OnClickListener {
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
SharedPreferences.Editor editor = preferences.edit();
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
LB = (Button) findViewById(R.id.loginbutton);
LB.setOnClickListener(this);
public void onClick(View view){
switch (view.getId()){
case R.id.loginbutton:
new LongOperation().execute("");
break;
}
}
public class LongOperation extends AsyncTask<String, Void, String>{ //string, void, string was added automatically
@Override
protected String doInBackground(String... params) {
SoapPrimitive result =(SoapPrimitive)envelope.getResponse();
String Something = result.toString();
editor.putString("sessionid",Something);
catch (Exception e){
e.printStackTrace(); }
return null;
} // closing bracket of do in background
}
当我尝试运行应用程序时，它会关闭，这就是我在日志中获得的错误
01-30 08:22:22.027: D/AndroidRuntime(11202): Shutting down VM
01-30 08:22:22.027: W/dalvikvm(11202): threadid=1: thread exiting with uncaught exception (group=0x4178ada0)
01-30 08:22:22.027: E/AndroidRuntime(11202): FATAL EXCEPTION: main
01-30 08:22:22.027: E/AndroidRuntime(11202): Process: com.datacom.caservicedesk, PID: 11202
01-30 08:22:22.027: E/AndroidRuntime(11202): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.datacom.caservicedesk/com.datacom.caservicedesk.Login}: java.lang.NullPointerException
01-30 08:22:22.027: E/AndroidRuntime(11202): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2233)
01-30 08:22:22.027: E/AndroidRuntime(11202): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2365)
01-30 08:22:22.027: E/AndroidRuntime(11202): at android.app.ActivityThread.access$800(ActivityThread.java:164)
01-30 08:22:22.027: E/AndroidRuntime(11202): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1258)
01-30 08:22:22.027: E/AndroidRuntime(11202): at android.os.Handler.dispatchMessage(Handler.java:102)
01-30 08:22:22.027: E/AndroidRuntime(11202): at android.os.Looper.loop(Looper.java:157)
01-30 08:22:22.027: E/AndroidRuntime(11202): at android.app.ActivityThread.main(ActivityThread.java:5350)
01-30 08:22:22.027: E/AndroidRuntime(11202): at java.lang.reflect.Method.invokeNative(Native Method)
01-30 08:22:22.027: E/AndroidRuntime(11202): at java.lang.reflect.Method.invoke(Method.java:515)
01-30 08:22:22.027: E/AndroidRuntime(11202): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
01-30 08:22:22.027: E/AndroidRuntime(11202): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
01-30 08:22:22.027: E/AndroidRuntime(11202): at dalvik.system.NativeStart.main(Native Method)
01-30 08:22:22.027: E/AndroidRuntime(11202): Caused by: java.lang.NullPointerException
01-30 08:22:22.027: E/AndroidRuntime(11202): at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:185)
01-30 08:22:22.027: E/AndroidRuntime(11202): at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:369)
01-30 08:22:22.027: E/AndroidRuntime(11202): at com.datacom.caservicedesk.Login.<init>(Login.java:53)
01-30 08:22:22.027: E/AndroidRuntime(11202): at java.lang.Class.newInstanceImpl(Native Method)
01-30 08:22:22.027: E/AndroidRuntime(11202): at java.lang.Class.newInstance(Class.java:1208)
01-30 08:22:22.027: E/AndroidRuntime(11202): at android.app.Instrumentation.newActivity(Instrumentation.java:1079)
01-30 08:22:22.027: E/AndroidRuntime(11202): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2224)
01-30 08:22:22.027: E/AndroidRuntime(11202): ... 11 more
01-30 08:26:13.387: W/ActivityThread(11709): Application com.datacom.caservicedesk can be debugged on port 8100...
01-30 08:26:13.407: D/AndroidRuntime(11709): Shutting down VM
01-30 08:26:13.407: W/dalvikvm(11709): threadid=1: thread exiting with uncaught exception (group=0x4178ada0)
01-30 08:26:13.417: E/AndroidRuntime(11709): FATAL EXCEPTION: main
01-30 08:26:13.417: E/AndroidRuntime(11709): Process: com.datacom.caservicedesk, PID: 11709
01-30 08:26:13.417: E/AndroidRuntime(11709): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.datacom.caservicedesk/com.datacom.caservicedesk.Login}: java.lang.NullPointerException
01-30 08:26:13.417: E/AndroidRuntime(11709): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2233)
01-30 08:26:13.417: E/AndroidRuntime(11709): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2365)
01-30 08:26:13.417: E/AndroidRuntime(11709): at android.app.ActivityThread.access$800(ActivityThread.java:164)
01-30 08:26:13.417: E/AndroidRuntime(11709): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1258)
01-30 08:26:13.417: E/AndroidRuntime(11709): at android.os.Handler.dispatchMessage(Handler.java:102)
01-30 08:26:13.417: E/AndroidRuntime(11709): at android.os.Looper.loop(Looper.java:157)
01-30 08:26:13.417: E/AndroidRuntime(11709): at android.app.ActivityThread.main(ActivityThread.java:5350)
01-30 08:26:13.417: E/AndroidRuntime(11709): at java.lang.reflect.Method.invokeNative(Native Method)
01-30 08:26:13.417: E/AndroidRuntime(11709): at java.lang.reflect.Method.invoke(Method.java:515)
01-30 08:26:13.417: E/AndroidRuntime(11709): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
01-30 08:26:13.417: E/AndroidRuntime(11709): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
01-30 08:26:13.417: E/AndroidRuntime(11709): at dalvik.system.NativeStart.main(Native Method)
01-30 08:26:13.417: E/AndroidRuntime(11709): Caused by: java.lang.NullPointerException
01-30 08:26:13.417: E/AndroidRuntime(11709): at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:185)
01-30 08:26:13.417: E/AndroidRuntime(11709): at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:369)
01-30 08:26:13.417: E/AndroidRuntime(11709): at com.datacom.caservicedesk.Login.<init>(Login.java:53)
01-30 08:26:13.417: E/AndroidRuntime(11709): at java.lang.Class.newInstanceImpl(Native Method)
01-30 08:26:13.417: E/AndroidRuntime(11709): at java.lang.Class.newInstance(Class.java:1208)
01-30 08:26:13.417: E/AndroidRuntime(11709): at android.app.Instrumentation.newActivity(Instrumentation.java:1079)
01-30 08:26:13.417: E/AndroidRuntime(11709): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2224)
01-30 08:26:13.417: E/AndroidRuntime(11709): ... 11 more