android - Problems reading from file -

if program starting first time, there no data in cache, data must downloaded server (with asynctask) , saved file.

public static string filename = "channels.txt";  fileoutputstream fos = null; objectoutputstream out = null; try {    fos = openfileoutput(filename, context.mode_append);    out = new objectoutputstream(fos);    out.writeobject(channelmanager.minstance);    out.close();    fos.close(); } 

main idea serialize object , write file later usage.

then try read it:

fileinputstream fis = null; objectinputstream in = null; try {    fis = openfileinput(filename);    in = new objectinputstream(fis);    mchannelmanager = (channelmanager) in.readobject();    log.e("mchannelmanager", mchannelmanager.getchannel_list().get(3) + "");    in.close();    fis.close();  }  

if try read after writen file, works fine, if close or kill app , try read file null pointer exception :/

i tried saving file name shared preferences , use it, still got null pointer exception (thought it's string/object/memory reference problem)

so (or might be) problem?

error log:

10-07 10:54:15.773  10630-10647/? e/cmc->nioclient3﹕ nioclient thread exception e: i/o exception while read message: 10-07 10:54:30.123  10741-10741/? e/apkinstallreceiver﹕ context = android.app.receiverrestrictedcontext@41597d68, intent.getaction() = android.intent.action.package_removed, intent.getdatastring() = package:com.iptviq.mobile.android.skynettv 10-07 10:54:31.393  12624-12624/com.iptviq.mobile.android.skynettv e/in cache﹕ + 10-07 10:54:31.413  12624-12624/com.iptviq.mobile.android.skynettv e/returning channel_list﹕ null 10-07 10:54:31.423  12624-12624/com.iptviq.mobile.android.skynettv e/androidruntime﹕    fatal exception: main java.lang.runtimeexception: unable start activity componentinfo{com.iptviq.mobile.android.skynettv/com.iptviq.mobile.android.engine.skynettvmainactivity}: java.lang.nullpointerexception         @ android.app.activitythread.performlaunchactivity(activitythread.java:2180)         @ android.app.activitythread.handlelaunchactivity(activitythread.java:2230)         @ android.app.activitythread.access$600(activitythread.java:141)         @ android.app.activitythread$h.handlemessage(activitythread.java:1234)         @ android.os.handler.dispatchmessage(handler.java:99)         @ android.os.looper.loop(looper.java:137)         @ android.app.activitythread.main(activitythread.java:5039)         @ java.lang.reflect.method.invokenative(native method)         @ java.lang.reflect.method.invoke(method.java:511)         @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:793)         @ com.android.internal.os.zygoteinit.main(zygoteinit.java:560)         @ dalvik.system.nativestart.main(native method)  caused by: java.lang.nullpointerexception         @ com.iptviq.mobile.android.engine.skynettvmainactivity.oncreate(skynettvmainactivity.java:202)         @ android.app.activity.performcreate(activity.java:5104)         @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1080)         @ android.app.activitythread.performlaunchactivity(activitythread.java:2144)             at android.app.activitythread.handlelaunchactivity(activitythread.java:2230)             at android.app.activitythread.access$600(activitythread.java:141)             at android.app.activitythread$h.handlemessage(activitythread.java:1234)             at android.os.handler.dispatchmessage(handler.java:99)             at android.os.looper.loop(looper.java:137)             at android.app.activitythread.main(activitythread.java:5039)             at java.lang.reflect.method.invokenative(native method)             at java.lang.reflect.method.invoke(method.java:511)             at com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:793)             at com.android.internal.os.zygoteinit.main(zygoteinit.java:560)             at dalvik.system.nativestart.main(native method) 

edit 2:

@override public void oncreate(bundle bundle) {     super.oncreate(bundle);     setcontentview(r.layout.activity_main);     activity = this;     preferences = getsharedpreferences("settings", mode_private);     server_ip = preferences.getstring("serverip", "192.168.37.14");     serverport = preferences.getstring("serverport", "8221");     arechannelsincache = preferences.getboolean("arechannelsincache", false);     filename = preferences.getstring("filename", filename);     if (!arechannelsincache) {         log.e("not in cache", "+");         mdownloadchannelstask = new downloadchannelstask();         mdownloadchannelstask.execute();     } else {         log.e("in cache", "+");         fileinputstream fis = null;         objectinputstream in = null;         try {             fis = openfileinput(filename);             in = new objectinputstream(fis);             mchannelmanager = (channelmanager) in.readobject();             log.e("mchannelmanager", mchannelmanager.getchannel_list().get(3) + "");             in.close();             fis.close();         } catch (ioexception ex) {             log.e("mchannelmanager", "error1 on reading " + ex);             ex.printstacktrace();         } catch (classnotfoundexception ex) {             log.e("mchannelmanager", "error2 on reading " + ex);             ex.printstacktrace();         }      } } 

asynctask works fine (to download data). when it's done calls handler saving file:

fileoutputstream fos = null; objectoutputstream out = null; try {     fos = openfileoutput(filename, context.mode_append);     out = new objectoutputstream(fos);     out.writeobject(channelmanager.minstance);     out.close();     fos.close();     log.e("saved file", ":)");     preferences.edit().putboolean("arechannelsincache", true).commit();     preferences.edit().putstring("filename", filename).commit();     } catch (ioexception ex) {     log.e("error @ main on saving data file", ":(( " + ex);     ex.printstacktrace();     } 

flush output stream before closing