How nscoding is used---archiving on iOS (how to change content).

In the previous chapter we introduced the archive on iOS and the solution, today we have a little change after the archive, so that the results after the solution is different, this method is similar to nsmutablexxx, can modify the parameters inside, let us take a look at it.

The method involved:

Seektofileoffset: This method is to seek the offset of the method, meaning to find the beginning of the text in the document.

Readdataoflength: This method refers to how long the file is read.

Offsetinfile: It means writing to the first position .

#import "ViewController.h"#definePZ NSLog (@ "----I'm a gorgeous split-line----");@interfaceViewcontroller ()@end@implementationViewcontroller- (void) viewdidload {[Super viewdidload]; NSString*path = [Nshomedirectory () stringByAppendingPathComponent:@"Documents/test.txt"];//NSLog (@ "%@", Path); //1. Create a file[[Nsfilemanager Defaultmanager] Createfileatpath:path contents:nil Attributes:nil]; NSString*str =@"Hello, world!.";        PZ; //2. Write-only way to open the file, Felehandleforwritingatpath is to return a write-only method.Nsfilehandle *writehanle =[Nsfilehandle Filehandleforwritingatpath:path]; //The string in str is stored in UTF8 encoded in data.NSData *data =[str datausingencoding:nsutf8stringencoding]; //Deposit the contents of data in Writehandle .[Writehanle Writedata:data]; //once again, it is added directly to the back of the previous string.[Writehanle Writedata:data];    PZ; //seektofileoffset:0 Jumps to the beginning of the file.[Writehanle Seektofileoffset:0]; //writes the string @ "xxx" to the Writehanle file in UTF8 encoding.[Writehanle writedata:[@"XXX"Datausingencoding:nsutf8stringencoding]]; //Offsetinfile is the number of points written to.NSLog (@"%llu", Writehanle.offsetinfile);    PZ; //4. Close the file[Writehanle CloseFile];    PZ; //use Fileurlwithpath to read the path of the path.Nsurl *url =[Nsurl Fileurlwithpath:path]; //and then pass the URL inside to Readhandle.Nsfilehandle *readhandle =[Nsfilehandle Filehandleforreadingfromurl:url Error:nil]; //Offsetinfile is the number of points written to.NSLog (@"%llu-----", Readhandle.offsetinfile); //Seektofileoffset: Is the offset of the specified file.[Readhandle Seektofileoffset:0]; //Readdataoflength: Reads 10 of the length of the Readhandle document.NSData *data1 = [Readhandle readdataoflength:Ten]; //The binary file data1 is stored in the NSString object str2 with UTF8 encoding.NSString *STR2 =[[NSString alloc]initwithdata:data1 encoding:nsutf8stringencoding]; //Close FileNSLog (@"%@", STR2); [Readhandle CloseFile];}- (void) didreceivememorywarning {[Super didreceivememorywarning]; //Dispose of any resources the can be recreated.}@end

Results of the output:

 the-Ten- +  +: A:58.407filehandledemo[13118:714260]3 the-Ten- +  +: A:58.407filehandledemo[13118:714260]0----- the-Ten- +  +: A:58.407filehandledemo[13118:714260] Xxxlo, WOR

How nscoding is used---archiving on iOS (how to change content).