LHF Objective-C语法（14）谓词

1、NSPredicate 谓词用于指定过滤条件，有点像SQL的查询条件，在计算机中表示计数真假值的函数，主要用于从集合分检出符合条件的对象，也可以用于字符串的正则匹配

例1

#import <Foundation/Foundation.h>@interface Person : NSObject { int pid; NSString *name; float height;}-(void) setPid:(int)pid;-(void) setName:(NSString*) name;-(void) setHeight:(float) height;-(int) pid;-(NSString*) name;-(float) height;@end//================================@implementation Person -(void) setPid:(int)p{ pid = p;}-(void) setName:(NSString*) n{ [n retain]; [name release]; name = n;}-(void) setHeight:(float) h{ height = h;}-(int) pid{ return pid;}-(NSString*) name{ return name;}-(float) height{ return height;}-(void) dealloc{ [name release]; [super dealloc];}@end//=======================================int main (int argc, const char * argv[]){ @autoreleasepool { NSMutableArray *array = [NSMutableArray arrayWithCapacity:5]; //实例化三个person放入数组 Person *p1 = [[Person alloc] init]; [p1 setPid:1]; [p1 setName:@"Tom"]; [p1 setHeight:168]; [array addObject:p1]; Person *p2 = [[Person alloc] init]; [p2 setPid:2]; [p2 setName:@"Ken"]; [p2 setHeight:178]; [array addObject:p2]; Person *p3 = [[Person alloc] init]; [p3 setPid:3]; [p3 setName:@"Tom"]; [p3 setHeight:188]; [array addObject:p3]; //创建谓词，条件是pid》1并且height《188 NSPredicate *pre = [NSPredicate predicateWithFormat:@"pid>1 and height<188"]; int i=0; for (;i<[array count]; i++) { Person *person = [array objectAtIndex:i]; //遍历数组，输出复合谓词条件的person的name if([pre evaluateWithObject:person]){ NSLog(@"%@",[person name]); } } [p1 release]; [p2 release]; [p3 release]; } return 0;}

NSPredicate *pre = [NSPredicate predicateWithFormat:@"pid>1 and height<188"];

如果pid不是person的成员变量，而是在person的成员变量xxx中，那么此处要写成xxx.pid>1

1、逻辑运算符  AND OR NOT

2、范围运算符  

      @"pid BETWEEN {1,5}"

      @"name IN {'Name1','Name2'}"

3、占位符

      NSPredicate *pre = [NSPredicate predicateWithFormat:@"name==$NAME"];

      NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"Name1",@"NAME",nil];

      NSPredicate *pre = [preTemplate predicateWithSubstitutionVariables:dic];

4、快速筛选数组

      NSPredicate *pre = [NSPredicate predicateWithFormat:@"pid>1"];

      NSMutableArray *arrayPre = [array filteredArrayUsingPredicate:pre];

      NSLog(@"%@",[[arrayPre objectAtIndex:0] name]);

5、字符串运算符

      @"name BEGINWITH[cd] 'na'"  判断name是否以na开头，[c]忽略大小写 [d]忽略重音字母

 6、LIKE运算符

      LIKE 使用？表示一个字符，＊表示多个字符

      @"name LIKE '???er*'" 与Paper Plane相匹配

7、SELF

      NSArray *arrays = [ NSArray arrayWithObjects:@"Apple",@"Goolge",@"MicroSoft",nil];

      NSPredicate *pre2 = [NSPredicate predicateWithFormat:@"SELF=='Apple'"];

8、正则表达式

      NSString *regex = @"^A.+e$";   以A开头，以e结尾

      NSPredicate *pre = [NSPredicate predicateWithFormat:@"SELF MATCHES %@",regex];

      if([pre evaluateWithObject:@"Apple"]){

            NSLog(@"YES");

      }else{

            NSLog(@"NO");
      }