Objective-c -- Analysis of attributes and member variables

As mentioned in the previous article, member variables are declared in a large pair of arc, while attributes are first declared by @ property and then synthesized by @ synthesize. Attribute is a new mechanism of OC language. In actual use, there are still many differences between the two.

Class member variables, through the permission modifier @ protected, @ private, @ public to change its access permission, and the attribute is belongs to the class object, by generating an object of this class, we can obtain its access permissions.

Firstclass. h

<Span style = "font-size: 12px;" >#import <Foundation/Foundation. h> @ interface firstclass: nsobject {// member variable of the class. The default access permission is protect int M. </span>

<Span style = "font-size: 12px;" >}// + class method + (void) classfun; //-indicates the instance method-(ID) initwithname :( nsstring *) aname andnum :( INT) N;-(void) print; @ property (nonatomic, strong) nsstring * Name; @ property (nonatomic, assign) int count; @ end </span> <span style = "font-size: 14px;"> </span>

In the header file, declare the (nsstring *) Name and (INT) Count variables. When @ property declares the variable, it will automatically generate the instance variable _ name starting with the following line, and _ count. and generate their setter and getter methods. When the @ synthesize merging attribute is omitted in the firstclass. m implementation file, the compiler automatically generates two instance variables: _ name and _ count.

<Span style = "font-size: 14px;"> // self. the attribute of the name access object. The _ name is the name of the instance and can be directly used, that is, self. name = _ name; </span>

Of course, this does not mean that @ synthesize does not work. @ synthesize variable = xxx. At this time, the actual operation object of self. variable is XXX rather than _ variable;

In the implementation file

@synthesize name;

The compiler automatically generates the instance variable of name and its corresponding setter and getter methods. Note that the generated instance variable is name rather than _ name.

The difference between "." and "->" in oC

Operations on objects in OC are implemented through pointer calls, and all member variables can be obtained through "->.

The "." operator is not available in the previous OC version. To adapt to the usage habits of Java, C ++, and other programmers, it is a new feature. "." In OC is actually a method call.

</PRE> </P> <P style = "margin-top: 0px; margin-bottom: 0px; font-family: Menlo; "> <PRE name =" code "class =" objc "> self. name = aname; <span style = "font-family: Menlo;"> //. setting the syntax to the left of the equal sign is equivalent to calling the setter method </span>

Nslog (@ "% @", self. Name); // put the. syntax to the right of the equal sign is equivalent to calling the getter Method

Below is the code for testing the above example

Firstclass. h

//// Firstclass. h // class property method member variable /// created by student on 14-9-17. // copyright (c) 2014 codebat. all rights reserved. // # import <Foundation/Foundation. h> @ interface firstclass: nsobject {// member variable of the class. The default access permission is protect @ public int M ;}// + class method + (void) classfun; //-indicates the instance method-(ID) initwithname :( nsstring *) aname andnum :( INT) N;-(void) print; @ property (nonatomic, strong) nsstring * Name; @ property (nonatomic, assign) int count; @ end

Firstclass. m

//// Firstclass. M // member variable of the class property method /// created by student on 14-9-17. // copyright (c) 2014 codebat. all rights reserved. // # import "firstclass. H "@ implementation firstclass @ synthesize name; // only name instances are generated at this time. _ name is not available @ synthesize COUNT = _ count; // specify the instance variable as _ count, this statement is omitted with the same effect + (void) classfun {nslog (@ "class method");}-(ID) initwithname :( nsstring *) aname andnum :( INT) m {If (Self = [Super init]) {self. name = aname; _ COUNT = m;} return self;}-(void) print {nslog (@ "% @ % d", self. name, self. count);} @ end

Main. m

//// Main. M // member variable of the class property method /// created by student on 14-9-17. // copyright (c) 2014 codebat. all rights reserved. // # import <Foundation/Foundation. h> # import "firstclass. H "int main (INT argc, const char * argv []) {@ autoreleasepool {firstclass * class = [[firstclass alloc] initwithname: @" doubi "andnum: 21]; class-> M = 20; Class. count = 22; [email protected] "SDS"; [class print];} return 0 ;}

Objective-c -- Analysis of attributes and member variables