OC Details, details of Public gun battles

OC Details, details of Public gun battles

Overview

• Copy: copy an object with the same content as the source object

• To copy data, you must comply with the following two Protocols:

  • NSCopying
  • NSMutableCopying

• Types of objects returned for copying

  • Variable, the object returned by the mutableCopy message
  • Immutable. The object returned by the copy message

• Copy type

  • The shortest copy only copies a pointer to the source object. No object is created and no memory is allocated.
  • Deep copy: Copies the source object, creates a new object, and allocates memory.

• Note:

  • The system processes the memory of the container class object and the non-container Class Object differently. That is, when an object not strongly referenced by other objects is removed from the container, the object will be destroyed.

Copy and Retain

• Copy

  • Is to create a new object, copy the content
  • Copy indicates that the content of the two objects is the same, and the reference count of the new object is 1.
  • It is irrelevant to the reference count of the old object, so the object does not change.
  • Copy reduces the context

• Retain

  • Creates a pointer and copies the pointer.
  • The object address is the same, and the content is the same.
  • Object reference count + 1

Copying behavior of different objects

• Non-container object (For example, NSString))

  • For immutable objects

    • Rules

      • Copy, shortest copy (pointer copy)
      • MutableCopy: Deep copy (Object copy). The returned object is variable (new variable object is generated)

    • Example

      -(Void) imutableInstanceCopy {NSString * string = @ "Welcome to Xcode"; // copy NSString * stringCopy = [string copy]; // mutableCopy, returned object variable NSMutableString * stringMutableCopy = [string mutableCopy]; [stringMutableCopy appendString :@"! "]; // The memory address of string and stringCopy is the same as that of NSLog (@" string: % p ", string); NSLog (@" strongCopy: % p ", stringCopy ); // The memory address of string and stringMutableCopy is different. A new memory NSLog (@ "stringMCopy: % p", stringMutableCopy) is allocated );}

  • For mutable objects

    • Rules

      • Copy, deep copy (Object copy), the returned object is unchangeable
      • MutableCopy, deep copy (Object copy)

    • Example

      -(Void) mutableInstanceCopy {NSMutableString * mutableString = [NSMutableString stringWithString: @ "Welcome to Xcode"]; // The returned object is an immutable NSString * stringCopy = [mutableString copy]. NSMutableString * mutableStringCopy = [mutableString copy]; // This statement reports an error during runtime. The error message "Attempt to mutate immutable object with appendString:" [mutableStringCopy appendString :@"~~~ "]; // Deep copy, returns the object variable NSMutableString * stringMutableCopy = [mutableString mutableCopy]; [stringMutableCopy appendString :@"! "]; // The memory addresses of the three and mutableString are different NSLog (@" mutableString: % p ", mutableString); NSLog (@" string: % p ", stringCopy ); NSLog (@ "mutableStringCopy: % p", mutableStringCopy); NSLog (@ "stringMutbleCopy: % p", stringMutableCopy );}

• Container object (NSArray)

  • Follow the non-container object copy Principle

  • Note:

    • The elements in the container are pointer assignments (Shortest copy)

    • Example

      -(Void) containerInstanceShallowCopy {NSArray * array = [NSArray arrayWithObjects: [NSMutableString stringWithString: @ "Welcome"], @ "to", @ "Xcode", nil]; // NSArray * arrayCopy = [array copy]; // NSMutableArray * arrayMutableCopy = [array mutableCopy]; NSLog (@ "array: % p", array ); NSLog (@ "arrayCopy: % p", arrayCopy); NSLog (@ "arrayMutableCopy: % p", arrayMutableCopy); // objects in the container are shortest copies, that is, they only have one NSMutableString * testString = [array objectAtIndex: 0] in the memory; [testString appendString: @ "you"]; // NSLog (@ "array [0]: % @", array [0]); NSLog (@ "arrayCopy [0]: % @ ", arrayCopy [0]); NSLog (@" arrayMutableCopy [0]: % @ ", arrayMutableCopy [0]);}

  • Implement deep replication in the true sense

    -(Void) containerInstanceDeepCopy {NSArray * array = [NSArray arrayWithObjects: [NSMutableString stringWithString: @ "Welcome"], @ "to", @ "Xcode", nil]; // The object in the array is a pointer copy NSArray * deepCopyArray = [[NSArray alloc] initWithArray: array]; // The above real deep copy, the objects in the array are NSArray * trueDeepCopyArray = [NSKeyedUnarchiver unarchiveObjectWithData: [NSKeyedArchiver attributes: array]; NSLog (@ "array: % p", array ); NSLog (@ "deepCopyArray: % p", deepCopyArray); NSLog (@ "trueDeepCopyArray: % p", trueDeepCopyArray); // change the first element of array [[array objectAtIndex: 0] appendString: @ "you"]; // only affects the NSLog (@ "array [0]: % @", array [0]), the first element of the deepCopyArray. NSLog (@ "arrayCopy [0]: % @", deepCopyArray [0]); // the first element of the trueDeepCopyArray array is not affected, is a real deep copy NSLog (@ "arrayMutableCopy [0]: % @", trueDeepCopyArray [0]);}

• Custom object

  • To copy an object, follow the NSCoping and NSMutableCoping protocols and implement the following methods:

    • -(Id) copyWithZone :( NSZone *) zone, variable copy
    • -(Id) mutableCopyWithZone :( NSZone *) zone, immutable copy

  • Example (copying a custom object Person)

    • Abide by the agreement and set Member attributes

      @ Interface Person: NSObject <NSCopying, NSMutableCopying>/** name */@ property (nonatomic, copy) NSMutableString * name;/** address */@ property (nonatomic, copy) NSString * address;/** age */@ property (nonatomic, assign) NSInteger age; @ end

    • Override Initialization Method

      -(Instancetype) init {if (self = [super init]) {self. name = [[NSMutableString alloc] initWithString: @ "XiaoYaowang"]; self. address = @ "Kong Shan new rain"; self. age = 3;} return self ;}

    • Implementation-(id) copyWithZone :( NSZone *) zone

      - (id)copyWithZone:(NSZone *)zone{    Person *p = [[[self class] allocWithZone:zone] init];    p.name = [self.name copy];    p.address = [self.address copy];    p.age =  self.age;    return p;}

    • Implementation-(id) mutableCopyWithZone :( NSZone *) zone

      -(Id) mutableCopyWithZone :( NSZone *) zone {Person * p = [[self class] allocWithZone: zone] init]; // note that the mutableCopy Method p is used here. name = [self. name mutableCopy]; p. address = [self. address copy]; p. age = self. age; return p ;}

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