Cocoa中谓词(Predicate)提供了一个通用的查询方式处理数据,可以获取和指定数据的过滤形式，Cocoa实际开发中可以是使用NSPredicate及其父类NSComparisonPredicate和NSCompoundPredicate.其风格类似于SQL查询语言和正则表达式的混合体，提供了具有表现力的，自然语言界面来定义一个集合被搜寻的逻辑条件。一般来说稍微操作过数据库基本上很容易理解其中的方法，至于使用的方法也很简单。
首先来一段比较简单的代码：
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF IN %@", @[@"keso", @"FlyElephant", @"博客园"]];
if ([predicate evaluateWithObject:@"keso"]) {
NSLog(@"keso");
};
第一行代码初始化一个查询条件，第二句就是判断数据在不在结果集中，跟SQL基本上一样，通过IN就能大概了解其功能，SELF表示本身，非常常用。
接下来可以类似于SQL中like语句的代码:
NSArray *array = [[NSArray alloc]initWithObjects:@"北京",@"上海",@"广州",@"深圳",nil];
NSPredicate *preBegin= [NSPredicate predicateWithFormat:@"SELF beginswith[c] %@",@"北"];
NSPredicate *preContain= [NSPredicate predicateWithFormat:@"SELF contains[c] %@",@"海"];
NSLog(@"%@",[array filteredArrayUsingPredicate:preBegin][0]);
NSLog(@"%@",[array filteredArrayUsingPredicate:preContain][0]);
第一次就是先初始化数组，然后创建条件，通过filteredArrayUsingPredicate过滤数组；
NSDictionary可以用谓词来过滤它的键和值（两者都为NSArray对象）;
NSOrderedSet可以由过滤的NSArray或NSSet生成一个新的有序的集，或者NSMutableSet可以简单的removeObjectsInArray来传递通过否定predicate过滤的对象。
NSPredicate谓词的在Core Data同样适用，在管理对象环境中，谓词由持久化存储助理（persistent store coordinator）评估，而集合则是内存中过滤。这时候我们有必要里了解一下基本比较运算符:
NSPredicate *betweenPredicate =
[NSPredicate predicateWithFormat: @"attributeName BETWEEN %@", @[@1, @10]];
NSDictionary *dictionary = @{ @"attributeName" : @5 };
BOOL between = [betweenPredicate evaluateWithObject:dictionary];
if (between) {
NSLog(@"比较运算符between");
}
NSString *regex = @"[A-Za-z]+";
NSPredicate *matchpredicate = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regex];
if ([matchpredicate evaluateWithObject:@"keso"]) {
NSLog(@"匹配成功");
}
@interface People : NSObject @property (strong,nonatomic) NSString *FirstName; @property (strong,nonatomic) NSString *LastName; @property (nonatomic) NSInteger Height; - (NSString *)description; @end
People.m文件:
@implementation People
- (NSString *)description {
return [NSString stringWithFormat:@"%@%@",self.LastName, self.FirstName];
};
@end
具体实现代码:
NSArray *firstNames =[[NSArray alloc]initWithObjects:@"泽东", @"恩来", @"介石", @"中山", nil];
NSArray *lastNames = @[ @"毛", @"周", @"蒋", @"孙" ];
NSArray *familiar = @[ @100, @99, @99, @98 ];
NSMutableArray *dataList= [NSMutableArray array];
[firstNames enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
People *people= [[People alloc] init];
people.FirstName = firstNames[idx];
people.LastName = lastNames[idx];
people.Height= [familiar[idx] integerValue];
[dataList addObject:people];
}];
NSPredicate *firstPredicate = [NSPredicate predicateWithFormat:@"FirstName = ‘恩来‘"];
NSPredicate *lastPredicate = [NSPredicate predicateWithFormat:@"LastName = %@", @"蒋"];
NSPredicate *heightPredicate = [NSPredicate predicateWithFormat:@"Height < 99"];
//名搜索
NSLog(@"名: %@",[dataList filteredArrayUsingPredicate:firstPredicate][0]);
//姓搜索
NSLog(@"姓: %@", [dataList filteredArrayUsingPredicate:lastPredicate][0]);
//知名度
NSLog(@"知名度: %@", [dataList filteredArrayUsingPredicate:heightPredicate][0]);
其实开始讲的NSCompoundPredicate和NSComparisonPredicate,因为有关系操作，基本上类似，如果通过混合搜索可以使用and，or实现，比如一下代码是等价的:
NSCompoundPredicate *comPredicate=[NSCompoundPredicate andPredicateWithSubpredicates:@[[NSPredicate predicateWithFormat:@"Height > 90"], [NSPredicate predicateWithFormat:@"FirstName = %@", @"介石"]]];
NSPredicate *secondPredicate=[NSPredicate predicateWithFormat:@"(Height > 90) AND (FirstName = %@)", @"介石"];
NSComparisonPredicate有两个调用的静态方法:
+ (NSComparisonPredicate *)predicateWithLeftExpression:(NSExpression *)lhs rightExpression:(NSExpression *)rhs modifier:(NSComparisonPredicateModifier)modifier type:(NSPredicateOperatorType)type options:(NSComparisonPredicateOptions)options; + (NSComparisonPredicate *)predicateWithLeftExpression:(NSExpression *)lhs rightExpression:(NSExpression *)rhs customSelector:(SEL)selector;
其实就是一个表达式的拼接的过程，不过具体的实现苹果给封装好了，一下是NSPredicateOperatorType类型:
typedef NS_ENUM(NSUInteger, NSPredicateOperatorType) {
NSLessThanPredicateOperatorType = 0, // compare: returns NSOrderedAscending
NSLessThanOrEqualToPredicateOperatorType, // compare: returns NSOrderedAscending || NSOrderedSame
NSGreaterThanPredicateOperatorType, // compare: returns NSOrderedDescending
NSGreaterThanOrEqualToPredicateOperatorType, // compare: returns NSOrderedDescending || NSOrderedSame
NSEqualToPredicateOperatorType, // isEqual: returns true
NSNotEqualToPredicateOperatorType, // isEqual: returns false
NSMatchesPredicateOperatorType,
NSLikePredicateOperatorType,
NSBeginsWithPredicateOperatorType,
NSEndsWithPredicateOperatorType,
NSInPredicateOperatorType, // rhs contains lhs returns true
NSCustomSelectorPredicateOperatorType,
NSContainsPredicateOperatorType NS_ENUM_AVAILABLE(10_5, 3_0) = 99, // lhs contains rhs returns true
NSBetweenPredicateOperatorType NS_ENUM_AVAILABLE(10_5, 3_0)
};
参考资料:https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/Predicates/Articles/pSyntax.html#//apple_ref/doc/uid/TP40001795-SW1
原文：http://www.cnblogs.com/xiaofeixiang/p/4264869.html