Check if there is a null type in the dictionary, and if so, convert to "" because the dictionary is null and cannot be deposited into the nsuserdefalut.

The method is to check whether there is nil in the dictionary, and nil to change into ""

-(Nsdictionary *) Checkdict: (Nsdictionary *) sender

{

Nsmutabledictionary * dict_mutable = [[Nsmutabledictionary alloc] init];

Nsarray * keys = Sender.allkeys;

For (NSString * key in keys) {

if ([[Sender Objectforkey:key] iskindofclass:[nsdictionary class]]) {

Nsdictionary * tempdict = [self checkdict:[sender objectforkey:key];

[Dict_mutable setobject:tempdict Forkey:key];

}

else{

if ([[sender Objectforkey:key] iskindofclass:[[nsnull null] class]]) {

[Dict_mutable setobject:@ "" Forkey:key];

}

else{

[Dict_mutable Setobject:[sender Objectforkey:key] forkey:key];

}

}

}

return dict_mutable;

}

Check if there is a null type in the dictionary, and if so, convert to "" because the dictionary is null and cannot be deposited into the nsuserdefalut.