谓词(NSPredicate)

OC中的谓词操作是针对于数组类型的，他就好比数据库中的查询操作，数据源就是数组，这样的好处是我们不需要编写很多代码就可以去操作数组，同时也起到过滤的作用，我们可以编写简单的谓词语句，就可以从数组中过滤出我们想要的数据。非常方便。

下面来看一下具体的例子吧：

Person.h

#import <Foundation/Foundation.h>  
  
@interface Person : NSObject  
  
@property NSString *name;  
@property NSInteger age;  
  
+ (id)personWithName:(NSString *)name andAge:(NSInteger)age;  
  
@end  

Person.m

#import "Person.h"  
  
@implementation Person  
  
+ (id)personWithName:(NSString *)name andAge:(NSInteger)age{  
    Person *person = [[Person alloc] init];  
    person.name = name;  
    person.age = age;  
    return person;  
}  
  
- (NSString *)description{  
    NSString *s =[NSString stringWithFormat:@"name=%@,age=%ld",_name,_age];  
    return s;  
}  
  
@end 

测试方法

        NSArray *persons = [NSArray arrayWithObjects:  
                            [Person personWithName:@"mac" andAge:20],  
                            [Person personWithName:@"1" andAge:30],  
                            [Person personWithName:@"2" andAge:40],  
                            [Person personWithName:@"3" andAge:50],  
                            [Person personWithName:@"4" andAge:60],  
                            [Person personWithName:@"5" andAge:70],  
                            [Person personWithName:@"6" andAge:20],  
                            [Person personWithName:@"7" andAge:40],  
                            [Person personWithName:@"8" andAge:60],  
                            [Person personWithName:@"9" andAge:40],  
                            [Person personWithName:@"0" andAge:80],  
                            [Person personWithName:@"10" andAge:90],  
                            [Person personWithName:@"1" andAge:20]];  
          
        //年龄小于30  
        //定义谓词对象，谓词对象中包含了过滤条件  
        NSPredicate *predicate = [NSPredicate predicateWithFormat:@"age<%d",30];  
        //使用谓词条件过滤数组中的元素，过滤之后返回查询的结果  
        NSArray *array = [persons filteredArrayUsingPredicate:predicate];  
        NSLog(@"filterArray=%@",array);  
          
        //查询name=1的并且age大于40  
        predicate = [NSPredicate predicateWithFormat:@"name='1' && age>40"];  
        array = [persons filteredArrayUsingPredicate:predicate];  
        NSLog(@"filterArray=%@",array);  
          
        //in(包含)  
        predicate = [NSPredicate predicateWithFormat:@"self.name IN {'1','2','4'} || self.age IN{30,40}"];  
          
        //name以a开头的  
        predicate = [NSPredicate predicateWithFormat:@"name BEGINSWITH 'a'"];  
        //name以ba结尾的  
        predicate = [NSPredicate predicateWithFormat:@"name ENDSWITH 'ba'"];  
          
        //name中包含字符a的  
        predicate = [NSPredicate predicateWithFormat:@"name CONTAINS 'a'"];  
          
        //like 匹配任意多个字符  
        //name中只要有s字符就满足条件  
        predicate = [NSPredicate predicateWithFormat:@"name like '*s*'"];  
        //?代表一个字符，下面的查询条件是：name中第二个字符是s的  
        predicate = [NSPredicate predicateWithFormat:@"name like '?s'"];