全局变量---只创建一次

定义方法：

#import <Foundation/Foundation.h>

@interface Model : NSObject
@property (strong,nonatomic)  NSString *name;
@property (strong,nonatomic)  NSString *age;
+(Model*)initWithName:(NSString*)name AndAge:(NSString*)age;

@end

#import "Model.h"

@implementation Model
+(Model*)initWithName:(NSString *)name AndAge:(NSString *)age
{
    
    static Model *model=nil;
    
    if (model==nil) {
        model=[[Model alloc]init];
        model.name=name;
        model.age=age;
    }
    return model;
}

@end

调用的时候：

在一个类中： Model *model =[Model initWithName:@"testName1" AndAge:@"1"];

在另一个类中：Model *model =[Model initWithName:@"testName2" AndAge:@"2"];

结果：   testName1     1