Cocoa提供了一個名為
NSPredicate的類，它用于指定過濾器的條件。可以創(chuàng)建NSPredicate對象，通過它準(zhǔn)確的描述所需的條件，通過謂詞篩選每個對象，判斷它們是否與條件相匹配。Cocoa用NSPredicate描述查詢的方式，原理類似于在數(shù)據(jù)庫中進行查詢，可以在數(shù)據(jù)庫風(fēng)格的API中使用NSPredicate類，比如Core Data和Spotlight。
代碼示例：
兩個對象類：Student和Teacher
//
// Student.h
// 謂詞
//
// Created by on 15/3/16.
// Copyright (c) 2015年 apple. All rights reserved.
//
#import <Foundation/Foundation.h>
@interface Student : NSObject
@property (nonatomic, retain) NSString *stuName;
@property (nonatomic, assign) NSInteger stuAge;
- (id)initWithName:(NSString *)name andAge:(NSInteger)age;
@end
//
// Student.m
// 謂詞
//
// 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
// 謂詞
//
// Created by on 15/3/16.
// Copyright (c) 2015年 apple. All rights reserved.
//
#import <Foundation/Foundation.h>
@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
// 謂詞
//
// 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
測試：
//
// main.m
// 謂詞
//
// Created by wujiafeng on 15/3/16.
// Copyright (c) 2015年 apple. All rights reserved.
//
#import <Foundation/Foundation.h>
#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];
// 設(shè)置teacher中的student對象
teacher.student = stu;
// 創(chuàng)建謂詞
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"student._stuName == 'Jack'"];
// 通知接收對象（即謂詞）根據(jù)指定的對象計算自身的值
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"];
// 迭代出年齡大于25歲的學(xué)生信息
for (Student *temp in stuArray) {
if ([pre evaluateWithObject:temp]) {
NSLog(@"姓名：%@，年齡：%ld", temp.stuName, temp.stuAge);
}
}
// 調(diào)用數(shù)組過濾器實現(xiàn)過濾
// 此方法會返回一個NSArray數(shù)組
NSArray *stus = [stuArray filteredArrayUsingPredicate:pre];
// 此方法是直接從NSMutableArray中過濾掉不滿足條件的項
[stuArray filterUsingPredicate:pre];
// KVC的運用
NSArray *stuNamesForMutable = [stuArray valueForKey:@"stuName"];
NSLog(@"%@", stuNamesForMutable);
NSLog(@"=======調(diào)用數(shù)組方法處理=======");
for (Student *temp in stus) {
NSLog(@"姓名：%@，年齡：%ld", temp.stuName, temp.stuAge);
}
// KVC的運用
NSArray *arryForStuName = [stus valueForKey:@"stuName"];
NSLog(@"%@", arryForStuName);
pre = [NSPredicate predicateWithFormat:@"_stuName == %@", @"Tom"];
// 這里的%K指的是鍵路徑
pre = [NSPredicate predicateWithFormat:@"%K == %@", @"_stuName", @"Tom"];
// 另一種方式是將變量名放入字符串中，類似于環(huán)境變量
NSPredicate *predicateTemplate = [NSPredicate predicateWithFormat:@"_stuName == $NAME"];
// 這里鍵是變量名（不包括美元符號），這里用字符串Jack作為鍵“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;
}
輸出結(jié)果如下：
2015-03-16 18:30:23.938 謂詞[581:15147] YES
2015-03-16 18:30:23.939 謂詞[581:15147] 姓名：jack6，年齡：26
2015-03-16 18:30:23.939 謂詞[581:15147] 姓名：jack7，年齡：27
2015-03-16 18:30:23.939 謂詞[581:15147] 姓名：jack8，年齡：28
2015-03-16 18:30:23.939 謂詞[581:15147] 姓名：jack9，年齡：29
2015-03-16 18:30:23.939 謂詞[581:15147] (
jack6,
jack7,
jack8,
jack9
)
2015-03-16 18:30:23.939 謂詞[581:15147] =======調(diào)用數(shù)組方法處理=======
2015-03-16 18:30:23.939 謂詞[581:15147] 姓名：jack6，年齡：26
2015-03-16 18:30:23.940 謂詞[581:15147] 姓名：jack7，年齡：27
2015-03-16 18:30:23.940 謂詞[581:15147] 姓名：jack8，年齡：28
2015-03-16 18:30:23.940 謂詞[581:15147] 姓名：jack9，年齡：29
2015-03-16 18:30:23.940 謂詞[581:15147] (
jack6,
jack7,
jack8,
jack9
)
2015-03-16 18:30:23.940 謂詞[581:15147] YES
