iOS 谓词的使用

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。在Java中是没有这种技术的，但是有开源的框架已经实现了此功能。

下面来看一下具体的例子吧：

Person.h

[objc] view plaincopy

//
// Person.h
// 46_NSPredicate
//
// Created by jiangwei on 14-10-18.
// Copyright (c) 2014年 jiangwei. All rights reserved.
//
#import <Foundation/Foundation.h>
@interface Person : NSObject
@property NSString *name;
@property NSInteger age;
+ (id)personWithName:(NSString *)name andAge:(NSInteger)age;
@end

Person.m

[objc] view plaincopy

//
// Person.m
// 46_NSPredicate
//
// Created by jiangwei on 14-10-18.
// Copyright (c) 2014年 jiangwei. All rights reserved.
//
#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

我们在Person类中定义属性，还有一个产生对象的类方法，同时重写了description方法，用于打印结果

测试方法

main.m

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//
// main.m
// 46_NSPredicate
//
// Created by jiangwei on 14-10-18.
// Copyright (c) 2014年 jiangwei. All rights reserved.
//
#import <Foundation/Foundation.h>
#import "Person.h"
//谓词，指定过滤器的条件，将符合条件的对象保留下来
//一般用谓词过滤数组中指定的元素
int main(int argc, const charchar * argv[]) {
@autoreleasepool {
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'"];
}
return 0;
}