IOS开发-NSPredicate谓词专题-白红宇

IOS开发-NSPredicate谓词专题

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发布时间：2019-06-22

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Cocoa提供了一个名为NSPredicate的类，它用于指定过滤器的条件。可以创建NSPredicate对象，通过它准确的描述所需的条件，通过谓词筛选每个对象，判断它们是否与条件相匹配。Cocoa用NSPredicate描述查询的方式，原理类似于在数据库中进行查询，可以在数据库风格的API中使用NSPredicate类，比如Core Data和Spotlight。

代码示例：

两个对象类：Student和Teacher

////  Student.h//  谓词////  Created by on 15/3/16.//  Copyright (c) 2015年 apple. All rights reserved.//#import 
    
     @interface Student : NSObject@property (nonatomic, retain) NSString *stuName;@property (nonatomic, assign) NSInteger stuAge;- (id)initWithName:(NSString *)name andAge:(NSInteger)age;@end

////  Student.m//  谓词////  Created by on 15/3/16.//  Copyright (c) 2015年 apple. All rights reserved.//#import "Student.h"@implementation Student- (id)initWithName:(NSString *)name andAge:(NSInteger)age {    if (self = [super init]) {        _stuName = name;        _stuAge = age;    }    return self;}@end

////  Teacher.h//  谓词////  Created by on 15/3/16.//  Copyright (c) 2015年 apple. All rights reserved.//#import 
    
     @class Student;@interface Teacher : NSObject@property (nonatomic, strong) Student *student;@property (nonatomic, retain) NSString *teaName;@property (nonatomic, assign) NSInteger teaAge;- (id)initWithName:(NSString *)name andAge:(NSInteger)age;@end

////  Teacher.m//  谓词////  Created by wujiafeng on 15/3/16.//  Copyright (c) 2015年 apple. All rights reserved.//#import "Teacher.h"@implementation Teacher- (id)initWithName:(NSString *)name andAge:(NSInteger)age {    if (self = [super init]) {        _teaName = name;        _teaAge = age;    }    return self;}@end

测试：

////  main.m//  谓词////  Created by wujiafeng on 15/3/16.//  Copyright (c) 2015年 apple. All rights reserved.//#import 
    
     #import "Student.h"#import "Teacher.h"int main(int argc, const char * argv[]) {    @autoreleasepool {        Student *stu = [[Student alloc] initWithName:@"Jack" andAge:12];        Teacher *teacher = [[Teacher alloc] initWithName:@"Tom" andAge:20];        //        设置teacher中的student对象        teacher.student = stu;        //        创建谓词        NSPredicate *predicate = [NSPredicate predicateWithFormat:@"student._stuName == 'Jack'"];//        通知接收对象（即谓词）根据指定的对象计算自身的值        BOOL match = [predicate evaluateWithObject:teacher];        NSLog(@"%s", (match) ? "YES" : "NO");                        NSMutableArray *stuArray = [NSMutableArray arrayWithCapacity:10];        for (int i = 0; i < 10; i++) {            Student *studentTemp = [[Student alloc] initWithName:[NSString stringWithFormat:@"jack%d", i] andAge:20 + i];            [stuArray addObject:studentTemp];        }                NSPredicate *pre = [NSPredicate predicateWithFormat:@"_stuAge > 25"];//        迭代出年龄大于25岁的学生信息        for (Student *temp in stuArray) {            if ([pre evaluateWithObject:temp]) {                NSLog(@"姓名：%@，年龄：%ld", temp.stuName, temp.stuAge);            }        }        //        调用数组过滤器实现过滤//        此方法会返回一个NSArray数组        NSArray *stus = [stuArray filteredArrayUsingPredicate:pre];        //        此方法是直接从NSMutableArray中过滤掉不满足条件的项        [stuArray filterUsingPredicate:pre];//        KVC的运用        NSArray *stuNamesForMutable = [stuArray valueForKey:@"stuName"];        NSLog(@"%@", stuNamesForMutable);                NSLog(@"=======调用数组方法处理=======");        for (Student *temp in stus) {            NSLog(@"姓名：%@，年龄：%ld", temp.stuName, temp.stuAge);        }        //        KVC的运用        NSArray *arryForStuName = [stus valueForKey:@"stuName"];        NSLog(@"%@", arryForStuName);                pre = [NSPredicate predicateWithFormat:@"_stuName == %@", @"Tom"];//        这里的%K指的是键路径        pre = [NSPredicate predicateWithFormat:@"%K == %@", @"_stuName", @"Tom"];                //        另一种方式是将变量名放入字符串中，类似于环境变量        NSPredicate *predicateTemplate = [NSPredicate predicateWithFormat:@"_stuName == $NAME"];//        这里键是变量名（不包括美元符号），这里用字符串Jack作为键“NAME”的值        NSDictionary *varDic = [NSDictionary dictionaryWithObjectsAndKeys:@"Jack", @"NAME", nil];        pre = [predicateTemplate predicateWithSubstitutionVariables:varDic];        BOOL match1 = [pre evaluateWithObject:stu];        NSLog(@"%s", (match1) ? "YES" : "NO");    }    return 0;}

输出结果如下：

2015-03-16 18:30:23.938 谓词[581:15147] YES

2015-03-16 18:30:23.939 谓词[581:15147] 姓名：jack6，年龄：26

2015-03-16 18:30:23.939 谓词[581:15147] 姓名：jack7，年龄：27

2015-03-16 18:30:23.939 谓词[581:15147] 姓名：jack8，年龄：28

2015-03-16 18:30:23.939 谓词[581:15147] 姓名：jack9，年龄：29

2015-03-16 18:30:23.939 谓词[581:15147] (

jack6,

jack7,

jack8,

jack9

)