Data Persistence for iPhone application development

IPhone applicationsDevelopmentDataPersistence is the content to be introduced in this article, mainly to learnIphone applicationsMediumDataLibrary usage. For details, see the details.

1. plist

Limitation: only the data types supported by this tool can be serialized and stored in plist. Other Cocoa objects cannot be stored in plist, or custom object storage.

Supported Data types: Array, Dictionary, Boolean, Data, Date, Number, and String.

Xml file data type ~ Where the basic Data is Boolean, Data, Date, Number, and String.), container Array, Dictionary)

Xml writing process: first write the basic data to the container and then call the writeToFile method of the container to write the data.

 
 

  
  
［theArray writeToFile:filePath atomically:YES]; 
 
 

The data types that have this method are ,:

The atomically parameter. Set the value to YES. When a file is written, data is not directly written to the specified path. Instead, the data is written to a "secondary File". After the file is successfully written, the data is copied to the specified path.

2. Archiver

Feature: supports complex data objects. Includes custom objects. Archive the custom object. The attributes of the object must meet the following requirements: int or float or ......), or an instance that implements the NSCoding protocol class. NSCoding is also required for the class of the custom object.

NSCoding method:

 
 

  
  
－id)initWithCoder:(NSCoder *)decoder; - (void)encodeWithCoder:(NSCoder *)encoder;  
 
 

The parameters are interpreted as decoded and encoded.

For example, create a custom class Student: NSObject <NSCoding>

 
 

  
  
#import "Student.h"   
  
  
@implementation Student   
  
  
@synthesize studentID;   
  
  
@synthesize studentName;   
  
  
@synthesize age;   
  
  
@synthesize count;   
  
  
- (void)encodeWithCoder:(NSCoder *)encoder  
  
  
{  
  
  
   [encoder encodeObject: studentID forKey: kStudentId];  
  
  
    [encoder encodeObject: studentName forKey: kStudentName];  
  
  
    [encoder encodeObject: age forKey: kAge];  
  
  
     [encoder encodeInt:count forKey:kCount];   
  
  
}18 19  - (id)initWithCoder:(NSCoder *)decoder  
  
  
{  
  
  
     if (self == [super init]) {  
  
  
       self.studentID = [decoder decodeObjectForKey:kStudentId];  
  
  
       self.studentName = [decoder decodeObjectForKey:kStudentName];          
  
  
   self.age = [decoder decodeObjectForKey:kAge];  
  
  
        self.count = [decoder decodeIntForKey:kCount];   
  
  
    }  
  
  
    return self;  
  
  
}  
  
  
@end 
 
 

Encoding Process:

 
 

  
  
/* Encoding */
  
  
Student * theStudent = [[Student alloc] init];
  
  
TheStudent. studentID = @ "Shenma ";
  
  
TheStudent. studentName = @ "shenma ";
  
  
TheStudent. age = @ "12 ";
  
  
NSMutableData * data = [NSMutableData alloc] init];
  
  
NSKeyedArchiver * archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData: data];
  
  
[Archiver encodeObject: theStudent forKey: @ "student"];
 
 

NSKeyedArchiver can be considered as a "encryptor". The student instance is encoded and stored in data

NSMutableData can be viewed as a "Container" for writing files (inherits NSData ).

Decoding process:

 
 

  
  
 /*unencoding*/  
  
  
Student *studento = [[Student alloc] init];  
  
  
data = [[NSData alloc] initWithContentsOfFile:documentsPath];  
  
  
 NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];  
  
  
 studento = [unarchiver decodeObjectForKey:@"student"];  
  
  
 [unarchiver finishDecoding]; 
 
 

Get the deserialized instance based on the key value.

3. SQLite

Database Operations ~

Summary: DetailsIPhone applicationsDevelopmentDataAfter the introduction of the persistent content, I hope this article will help you!