Error message Nserror

First, get the error message of the system

For example, when moving files, get file operation error:

Nserror *e = nil;
[[Nsfilemanager Defaultmanager] Moveitematpath:sourcepath topath:targetpath error:&e];
if (e) {
NSLog (@ "Move failed:%@", [e Localizeddescription]);
}

To set an empty error message first

Nserror *e = nil;

Fetch Address

&e   

If there is an error message, print the localized description of the error

if (e) {NSLog (@ "Move failed:%@", [e Localizeddescription]);}

Ii.. Custom error messages

You can usually customize a Nserror object by using the following statement

#define Customerrordomain @ "com.xiaodao.test"  typedef enum {  xdefultfailed = -1000,  xregisterfailed, 
   
    xconnectfailed,  xnotbindedfailed  }customerrorfailed;
   

Nsdictionary *userinfo = [Nsdictionary dictionarywithobject:@ "is a error test"                                                                      Forkey:nslocalizeddescriptionkey];

Nserror *aerror = [Nserror errorwithdomain:customerrordomain code:xdefultfailed Userinfo:userinfo];

Where the custom error domain object is customerrordomain, usually with the domain name reversed, or any other string

Code error ID, the system code is generally greater than 0, custom code can be enumerated (preferably with negative numbers, but not necessary)

UserInfo custom error message, Nslocalizeddescriptionkey is a pre-defined key in the Nserror header file that identifies the localized description of the error

The corresponding value information can be obtained by Nserror's Localizeddescription method.

The main calling function typically passes a pointer to the Nserror pointer to get an error message, such as

-(Bool) dosomething: (nsdictionary *) Parameter1 Error: (Nserror *) aerror{   //todo:do Something
*aerror = [Nserror errorwithdomain:customerrordomain code:xdefultfailed Userinfo:userinfo];
return Yes;

}

Third, Nserror header file parsing

There are three main private variables in a 1.NSError object

Error domain (Nsinteger): _domain

Error indication (nsstring *): _code

Error details (nsdictionary *): _userinfo

Usually identify an error message together with _domain and _code

Get _domain

-(NSString *) domain;

Get _code

-(Nsinteger) code;

Get _userinfo

-(Nsdictionary *) UserInfo;

2. Predefined domains

Major error domains in the AppKit and foundation libraries

NSString *const Nscocoaerrordomain;

Other domains

NSString *const Nsposixerrordomain; NSString *const Nsosstatuserrordomain; NSString *const Nsmacherrordomain;

3. Pre-defined UserInfo key name

Recommended standard method, universal key

NSString *const Nsunderlyingerrorkey;

Other keys, corresponding to the method of reading information:

Detailed Description key

NSString *const Nslocalizeddescriptionkey;

Fetch method

-(NSString *) localizeddescription;

Failure reason Key

NSString *const Nslocalizedfailurereasonerrorkey

Fetch method

-(NSString *) Localizedfailurereason;

Restore Suggestion Key

NSString *const Nslocalizedrecoverysuggestionerrorkey;

Fetch method

-(NSString *) localizedrecoverysuggestion;

Recovery Option key

NSString *const Nslocalizedrecoveryoptionserrorkey

Fetch method

-(Nsarray *) localizedrecoveryoptions;

Other keys

NSString *const Nsrecoveryattemptererrorkey; NSString *const Nshelpanchorerrorkey; NSString *const Nsstringencodingerrorkey; NSString *const Nsurlerrorkey; NSString *const Nsfilepatherrorkey;

Usage:

Nsdictionary *userinfo = [Nsdictionary dictionarywithobjectsandkeys:@ "This is a detailed description of the error", Nslocalizeddescriptionkey, error , Nsunderlyingerrorkey, Nil]];

4. The main initialization method:

-(ID) Initwithdomain: (NSString *) Domain code: (nsinteger) code userInfo: (nsdictionary *) dict;

+ (ID) Errorwithdomain: (NSString *) Domain code: (nsinteger) code userInfo: (nsdictionary *) dict;

Error message Nserror