ios - Error during storing values in plist file -

i have stepper, during change of value need store values in plist.

so according saveappplist method need pass nsmutabledictionary changed file -> dictdata

nsdata *plistdata = [nspropertylistserialization datafrompropertylist:dictdata format:nspropertylistxmlformat_v1_0 errordescription:&error]; if(plistdata) {     [plistdata writetofile:plistpath atomically:yes]; } 

and here method stepper:

-(void)changeitemquantityatrow:(int)row                        tovalue:(double)value {     nsmutabledictionary *item = [[items objectatindex:row] mutablecopy];     [item setobject:[nsnumber numberwithdouble:value] forkey:@"quantity"];     [items setobject:item atindexedsubscript:row];     nslog(@"%@", items);     nsmutabledictionary *plistdict = [nsdictionary dictionarywithobjects:items forkeys:[nsarray arraywithobjects:@"name", @"price", @"quantity", nil]];     nslog(@"%@", plistdict);     [self saveappplist:plistdict]; } 

and plist looks (this 1 of 4 items):

<dict>     <key>items</key>     <array>         <dict>             <key>name</key>             <string>the 0 item</string>             <key>price</key>             <integer>133</integer>             <key>quantity</key>             <integer>17</integer>         </dict> 

the stepper changing quantity of item. have error when try change value of quantity:

'nsinvalidargumentexception', reason: '*** -[nsdictionary initwithobjects:forkeys:]: count of objects (4) differs count of keys (3)' 

i understand source of error don't know how can solve issue. can me? , 1 more - may it's not store value after every tap on stepper?

forget want store array, think of object id instance. want store id items key @"items", want use

//[nsdictionary dictionarywithobject:<#(id)#> forkey:<#(id<nscopying>)#>] nsmutabledictionary *plistdict = [nsdictionary dictionarywithobject:items forkey:@"items"];