java - Storing and getting values from sharedpreferences in android -
i want store values in sharedpreferences , getting values sharedpreferences display values in listview. next want remove values list when click on longpress on specific value .after removing values status updated in sharedpreferences. done 1 problem when close application , open again have display sharedpreferences vales in listview. display nullpointerexeption,
actually requirement 1)storing values in sharedpreferences , display values in listview every click .allowed 5 values.and list values available in onresume() method also. 2) when long press on specific value of listview have remove , and updated values stored in sharedpreferences also.
my code
public class listviewdemo1 extends activity { /** * called when activity first created. */ button btn; static int count; private listview list; public static arraylist<string> values = new arraylist<string>(); arraylist countlist = new arraylist(); private arrayadapter adapter; sharedpreferences shared; editor editor; private static arraylist<string> sharedlist; @override public void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.main); list = (listview) findviewbyid(r.id.list); btn = (button) findviewbyid(r.id.btn); shared = this.getsharedpreferences("myprefernces", context.mode_world_writeable); editor = shared.edit(); btn.setonclicklistener(new onclicklistener() { public void onclick(view v) { // todo auto-generated method stub sharedlist = new arraylist(); count++; if (count == 1) { values.add("one"); countlist.add(count); } if (count == 2) { values.add("two"); countlist.add(count); } if (count == 3) { values.add("three"); countlist.add(count); } if (count == 4) { values.add("four"); countlist.add(count); } if (count == 5) { values.add("five"); countlist.add(count); } if (count > 5) { --count; toast.maketext(getapplicationcontext(), "" + count, 100).show(); } //put values sharedpreferences editor.putint("size", values.size()); (int = 0; < values.size(); i++) { editor.putstring("addr" + i, values.get(i)); } editor.commit(); // getting values sharedpreference int size = shared.getint("size", 0); (int k = 0; k < size; k++) { sharedlist.add(shared.getstring("addr" + k, "")); } adapter = new arrayadapter(listviewdemo1.this, android.r.layout.simple_list_item_1, sharedlist); list.setadapter(adapter); } }); list.setonitemlongclicklistener(new onitemlongclicklistener() { public boolean onitemlongclick(adapterview<?> arg0, view arg1, int arg2, long arg3) { // todo auto-generated method stub --count; values.remove(arg2); sharedlist.remove(arg2); editor.clear(); editor.commit(); editor.putint("size", sharedlist.size()); (int = 0; < sharedlist.size(); i++) { editor.putstring("addr" + i, sharedlist.get(i)); } editor.commit(); adapter.notifydatasetchanged(); return true; } }); } @override protected void onresume() { // todo auto-generated method stub super.onresume(); if (sharedlist.size() > 0) { adapter = new arrayadapter(listviewdemo1.this, android.r.layout.simple_list_item_1, sharedlist); list.setadapter(adapter); } } } logcat
04-21 09:56:02.142: e/androidruntime(1160): fatal exception: main 04-21 09:56:02.142: e/androidruntime(1160): java.lang.runtimeexception: unable resume activity {com.views/com.views.listviewdemo1}: java.lang.nullpointerexception 04-21 09:56:02.142: e/androidruntime(1160): @ android.app.activitythread.access$600(activitythread.java:141) 04-21 09:56:02.142: e/androidruntime(1160): @ android.app.activitythread$h.handlemessage(activitythread.java:1234) 04-21 09:56:02.142: e/androidruntime(1160): @ android.os.handler.dispatchmessage(handler.java:99) 04-21 09:56:02.142: e/androidruntime(1160): @ android.os.looper.loop(looper.java:137) 04-21 09:56:02.142: e/androidruntime(1160): @ android.app.activitythread.main(activitythread.java:5041) 04-21 09:56:02.142: e/androidruntime(1160): @ java.lang.reflect.method.invokenative(native method) 04-21 09:56:02.142: e/androidruntime(1160): @ java.lang.reflect.method.invoke(method.java:511) 04-21 09:56:02.142: e/androidruntime(1160): @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:793) 04-21 09:56:02.142: e/androidruntime(1160): @ com.android.internal.os.zygoteinit.main(zygoteinit.java:560) 04-21 09:56:02.142: e/androidruntime(1160): @ dalvik.system.nativestart.main(native method) 04-21 09:56:02.142: e/androidruntime(1160): caused by: java.lang.nullpointerexception 04-21 09:56:02.142: e/androidruntime(1160): @ com.views.listviewdemo1.onresume(listviewdemo1.java:114) 04-21 09:56:02.142: e/androidruntime(1160): @ android.app.instrumentation.callactivityonresume(instrumentation.java:1185)
you instantiate sharedlist in onclick() method of button. method not called when activity resumed , sharedlist null.
you need check if it's not null:
@override protected void onresume() { // todo auto-generated method stub super.onresume(); if(sharedlist != null && sharedlist.size()>0){ adapter=new arrayadapter(listviewdemo1.this,android.r.layout.simple_list_item_1,sharedlist); list.setadapter(adapter); } } 
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