LHF Objective-C语法（14）谓词

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#float #apple #microsoft #regex #正则表达式 #arrays

本文介绍了NSPredicate的基本概念及其在Objective-C中的应用。通过实例演示了如何利用NSPredicate进行复杂的数据筛选，包括逻辑运算、范围查询、字符串匹配等，并展示了如何通过正则表达式增强筛选能力。

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"];