iphone - Why can't I write Dictionary to plist? -

hey all,i got weird problem here
first create small project try write dictionary plist
declared textfield , button , code ibaction:

nsarray *localpathstemp   = nssearchpathfordirectoriesindomains(nsdocumentdirectory, nsuserdomainmask, yes); nsstring *localdocpathtemp    = [localpathstemp objectatindex:0]; nsstring *localfilepathtemp   = [localdocpathtemp stringbyappendingpathcomponent:@"inputpassword.plist"]; nsmutabledictionary *localdictreadtemp  = [[nsmutabledictionary alloc] initwithcontentsoffile:localfilepathtemp]; nsmutabledictionary *localserialnumber = [nsmutabledictionary dictionarywithobject:setsn.text                                                                                 forkey:@"input_serial_number"]; 

i try log write in

nslog(@"local dictionary : %@",[localdictreadtemp valueforkey:@"input_serial_number"]);//"input_serial_number=1" nslog(@"dictionary-localserialnumber %@",[localserialnumber valueforkey:@"input_serial_number"]);//1(i enter 1 @ textfield) 

it's woks fine think

but move whole project

i got null

this code in original project(in alertview)

nsarray *localpathstemp   = nssearchpathfordirectoriesindomains(nsdocumentdirectory, nsuserdomainmask, yes); nsstring *localdocpathtemp    = [localpathstemp objectatindex:0]; nsstring *localfilepathtemp   = [localdocpathtemp stringbyappendingpathcomponent:@"inputpassword.plist"]; nsmutabledictionary *localdictreadtemp  = [[nsmutabledictionary alloc] initwithcontentsoffile:localfilepathtemp]; nsmutabledictionary *localserialnumber = [nsmutabledictionary dictionarywithobject:setlocalserialnumber.text                                                                                         forkey:@"input_serial_number"]; [localdictreadtemp addentriesfromdictionary:localserialnumber]; [localdictreadtemp writetofile:localfilepathtemp atomically:yes];   nslog(@"text in textfield:%@",setlocalserialnumber.text); nslog(@"local dictionary %@",localserialnumber);//"input_serial_number" = 1  nslog(@"dictionary-localdictreadtemp %@",[localdictreadtemp valueforkey:@"input_serial_number"]);//null 

last result null

that's problem can't figure out,i got value @ sample ,but not work here .

why...did give wrong file path or ... ?

thanks replys

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more information project

my application use control hardware device
if user first time use application
user have enter password , device serial number
device use bonjour search device
, default serial number/password url(this case in wifi)
ex.the url http://11.33.44.65/defaultsn_pwd.php

i plist file :

{      sn  = 1;       pwd = 777; } 

this information user can't see it.
, application pop alertview 2 textfields
if text in textfield match sn/pwd form url
write in.
!!!if user in 3g environment , connect server control device
different wifi,because have give server device serial number

so

1. enter serial number(i need write in plist on iphone,but got null here)

2. take serial part of new url ex.http://server/defaultsn_pwd.php?sn=1

because can't write serial number in plist ,so can't right url
url http://server/defaultsn_pwd.php?sn=null
crash program

this avery deadly issues ,please me figure problem out....

i trapped in problem long...

nsmutabledictionary *localdictreadtemp  = [[nsmutabledictionary alloc] initwithcontentsoffile:localfilepathtemp]; 

i betcha problem line. unless writing file location elsewhere in code, there no file @ localfilepathtemp. since file empty, initwithcontentsoffile returns nil dictionary, , rest chain reaction of nil objects.

try this:

if ([[nsfilemanager defaultmanager] fileexistsatpath:localfilepathtemp]) {     nslog(@"file exists @ %@",localfilepathtemp); } else nslog(@"some dude internet solved problem, should go choose answer");