原文網址:http://blog.csdn.net/jiangwei0910410003/article/details/41923507
OC中的謂詞操作是針對於數組類型的,他就好比數據庫中的查詢操作,數據源就是數組,這樣的好處是我們不需要編寫很多代碼就可以去操作數組,同時也起到過濾的作用,我們可以編寫簡單的謂詞語句,就可以從數組中過濾出我們想要的數據。非常方便。在Java中是沒有這種技術的,但是有開源的框架已經實現了此功能。
下面來看一下具體的例子吧:
Person.h
- //
- // Person.h
- // 46_NSPredicate
- //
- // Created by jiangwei on 14-10-18.
- // Copyright (c) 2014年 jiangwei. All rights reserved.
- //
- #import <Foundation/Foundation.h>
- @interface Person : NSObject
- @property NSString *name;
- @property NSInteger age;
- + (id)personWithName:(NSString *)name andAge:(NSInteger)age;
- @end
- //
- // Person.m
- // 46_NSPredicate
- //
- // Created by jiangwei on 14-10-18.
- // Copyright (c) 2014年 jiangwei. All rights reserved.
- //
- #import "Person.h"
- @implementation Person
- + (id)personWithName:(NSString *)name andAge:(NSInteger)age{
- Person *person = [[Person alloc] init];
- person.name = name;
- person.age = age;
- return person;
- }
- - (NSString *)description{
- NSString *s =[NSString stringWithFormat:@"name=%@,age=%ld",_name,_age];
- return s;
- }
- @end
測試方法
main.m
- //
- // main.m
- // 46_NSPredicate
- //
- // Created by jiangwei on 14-10-18.
- // Copyright (c) 2014年 jiangwei. All rights reserved.
- //
- #import <Foundation/Foundation.h>
- #import "Person.h"
- //謂詞,指定過濾器的條件,將符合條件的對象保留下來
- //一般用謂詞過濾數組中指定的元素
- int main(int argc, const charchar * argv[]) {
- @autoreleasepool {
- NSArray *persons = [NSArray arrayWithObjects:
- [Person personWithName:@"mac" andAge:20],
- [Person personWithName:@"1" andAge:30],
- [Person personWithName:@"2" andAge:40],
- [Person personWithName:@"3" andAge:50],
- [Person personWithName:@"4" andAge:60],
- [Person personWithName:@"5" andAge:70],
- [Person personWithName:@"6" andAge:20],
- [Person personWithName:@"7" andAge:40],
- [Person personWithName:@"8" andAge:60],
- [Person personWithName:@"9" andAge:40],
- [Person personWithName:@"0" andAge:80],
- [Person personWithName:@"10" andAge:90],
- [Person personWithName:@"1" andAge:20]];
- //年齡小於30
- //定義謂詞對象,謂詞對象中包含了過濾條件
- NSPredicate *predicate = [NSPredicate predicateWithFormat:@"age<%d",30];
- //使用謂詞條件過濾數組中的元素,過濾之後返回查詢的結果
- NSArray *array = [persons filteredArrayUsingPredicate:predicate];
- NSLog(@"filterArray=%@",array);
- //查詢name=1的並且age大於40
- predicate = [NSPredicate predicateWithFormat:@"name='1' && age>40"];
- array = [persons filteredArrayUsingPredicate:predicate];
- NSLog(@"filterArray=%@",array);
- //in(包含)
- predicate = [NSPredicate predicateWithFormat:@"self.name IN {'1','2','4'} || self.age IN{30,40}"];
- //name以a開頭的
- predicate = [NSPredicate predicateWithFormat:@"name BEGINSWITH 'a'"];
- //name以ba結尾的
- predicate = [NSPredicate predicateWithFormat:@"name ENDSWITH 'ba'"];
- //name中包含字符a的
- predicate = [NSPredicate predicateWithFormat:@"name CONTAINS 'a'"];
- //like 匹配任意多個字符
- //name中只要有s字符就滿足條件
- predicate = [NSPredicate predicateWithFormat:@"name like '*s*'"];
- //?代表一個字符,下面的查詢條件是:name中第二個字符是s的
- predicate = [NSPredicate predicateWithFormat:@"name like '?s'"];
- }
- return 0;
- }
然後我們就可以使用NSPredicate類進行過濾操作了
1、查詢數組中年齡小於30的對象
- //年齡小於30
- //定義謂詞對象,謂詞對象中包含了過濾條件
- NSPredicate *predicate = [NSPredicate predicateWithFormat:@"age<%d",30];
- //使用謂詞條件過濾數組中的元素,過濾之後返回查詢的結果
- NSArray *array = [persons filteredArrayUsingPredicate:predicate];
- NSLog(@"filterArray=%@",array);
- //定義謂詞對象,謂詞對象中包含了過濾條件
- NSPredicate *predicate = [NSPredicate predicateWithFormat:@"age<%d",30];
然後進行過濾操作,返回一個過濾之後的數組對象
- //使用謂詞條件過濾數組中的元素,過濾之後返回查詢的結果
- NSArray *array = [persons filteredArrayUsingPredicate:predicate];
- //查詢name=1的並且age大於40
- predicate = [NSPredicate predicateWithFormat:@"name='1' && age>40"];
- array = [persons filteredArrayUsingPredicate:predicate];
- NSLog(@"filterArray=%@",array);
3、包含語句的使用
- //in(包含)
- predicate = [NSPredicate predicateWithFormat:@"self.name IN {'1','2','4'} || self.age IN{30,40}"];
- //name以a開頭的
- predicate = [NSPredicate predicateWithFormat:@"name BEGINSWITH 'a'"];
- //name以ba結尾的
- predicate = [NSPredicate predicateWithFormat:@"name ENDSWITH 'ba'"];
- //name中包含字符a的
- predicate = [NSPredicate predicateWithFormat:@"name CONTAINS 'a'"];
- //like 匹配任意多個字符
- //name中只要有s字符就滿足條件
- predicate = [NSPredicate predicateWithFormat:@"name like '*s*'"];
- //?代表一個字符,下面的查詢條件是:name中第二個字符是s的
- predicate = [NSPredicate predicateWithFormat:@"name like '?s'"];
這一篇就介紹了OC中常用的技術:謂詞的使用,他用起來很方便的,而且也沒什麼難度,和我們當初在操作數據庫的時候很想,但是他對我們進行過濾操作提供了很大的便捷。