OC之NSPredicate(谓词)学习

NSPredicate(谓词)

谓词：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。

实例：

定义一个person类


@interface Person : NSObject
@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) int age;
+ (instancetype)personWithName:(NSString *)name andAge:(int)age;
@end
//便利初始化方法，直接初始化一个对象
+ (instancetype)personWithName:(NSString *)name andAge:(int)age
{
    Person *person = [[Person alloc]init];
    person.name = name;
    person.age = age;
    return person;
}
- (NSString *)description
{
    NSString *desc = [NSString stringWithFormat:@"name:%@,age:%d",_name,_age];
    return desc;
}

创建一个数组，用来存放person类的对象

 NSArray *personArray = @[
                          [Person personWithName:@"niuer" andAge:12],
                          [Person personWithName:@"zhangsan" andAge:13],
                          [Person personWithName:@"lisi" andAge:14],
                          [Person personWithName:@"wangwu" andAge:15],
                          [Person personWithName:@"Zhaoliu" andAge:16],
                          [Person personWithName:@"tianqi" andAge:17],
                      ];

谓词的基本用法

关系运算符 > < =

 NSPredicate *predicate = [NSPredicate predicateWithFormat:@"self.age > 12 "];
NSArray *result = [personArray filteredArrayUsingPredicate:predicate];
NSLog(@"%@",result);
predicate = [NSPredicate predicateWithFormat:@"self.age < 15"];
result = [personArray filteredArrayUsingPredicate:predicate];
NSLog(@"%@",result);
predicate = [NSPredicate predicateWithFormat:@"self.age = 15"];
result = [personArray filteredArrayUsingPredicate:predicate];
NSLog(@"%@",result);

逻辑运算符 &&（and) ||(或）
 predicate = [NSPredicate predicateWithFormat:@"self.age < 17 && self.age > 12"];
result = [personArray filteredArrayUsingPredicate:predicate];
NSLog(@"%@",result);
predicate = [NSPredicate predicateWithFormat:@"self.age > 15 || self.name = 'niuer' "];
result = [personArray filteredArrayUsingPredicate:predicate];
NSLog(@"%@",result);

. ANY(至少一个) ALL(所有)

 predicate = [NSPredicate predicateWithFormat:@"ALL self.age < 12"];
if ([predicate evaluateWithObject:personArray]) {
    NSLog(@"所有人都小于12");
}else{
    NSLog(@"所有人都大于12");
}
predicate = [NSPredicate predicateWithFormat:@"any self.age < 15"];
if ([predicate evaluateWithObject:personArray]) {
    NSLog(@"至少有一个人小于15");
}else{
    NSLog(@"所有人都大于15");
}

范围运算符 between(闭区间) in(包含)

  predicate = [NSPredicate predicateWithFormat:@"self.age between {13,15}"];
  result = [personArray filteredArrayUsingPredicate:predicate];
  NSLog(@"%@",result);
  predicate = [NSPredicate predicateWithFormat:@"self.age in{13,15} || self.name in {'zhangsan','lisi'}"];
  result = [personArray filteredArrayUsingPredicate:predicate];
  NSLog(@"%@",result);

字符串的操作

 下面三个指令一般都加[cd] c:不区分大小写，d  不区分重高音
  beginswit h:以..开始
  endswith  :以..结束
  contains :包含... 
  predicate = [NSPredicate predicateWithFormat:@"self.name beginswith[cd] 'z' "];
 predicate = [NSPredicate predicateWithFormat:@"self.name beginswith[cd] 'z' "];
  result = [personArray filteredArrayUsingPredicate:predicate];
  NSLog(@"%@",result);
  predicate = [NSPredicate predicateWithFormat:@"self.name endswith 'i' "];
  result = [personArray filteredArrayUsingPredicate:predicate];
  NSLog(@"%@",result);
  predicate = [NSPredicate predicateWithFormat:@"self.name contains 'i' "];
  result = [personArray filteredArrayUsingPredicate:predicate];
  NSLog(@"%@",result);

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