IOS中谓词的使用

2020-01-01 本文已影响0人 lenka01

何为“谓词”，即大家所熟悉的NSPredicate。

谓词表达式

说到谓词，少不了谓词表达式，谓词表达式有三个部分组成：表达式、运算符、返回值。谓词表达式必须返回一个BOOL类型的值。
那它能为我们做些什么呢？接下来开始一一道来。

谓词定义

常用的谓词定义方法有两种：

[NSPredicate predicateWithFormat:@""]

[NSPredicate predicateWithBlock:(BOOL (^)(id _Nullable evaluatedObject, NSDictionary<NSString *, id> * _Nullable bindings))block

predicateWithBlock需要在block中写比较逻辑。
例如：

    Model *model0 = [self createModel:@"jane" age:10];
    Model *model1 = [self createModel:@"tim1" age:20];
    Model *model2 = [self createModel:@"tim2" age:21];
    Model *model3 = [self createModel:@"tim3" age:22];
    Model *model4 = [self createModel:@"tim4" age:23];
    Model *model5 = [self createModel:@"Tim6" age:11];
    NSArray *array = @[model0,model1,model2,model3,model4,model5];
    NSLog(@"filter0:%@",[array filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"SELF.age BETWEEN {10,15} AND SELF.name BEGINSWITH[cd] %@",@"tim"]]);
    NSLog(@"filter00:%@",[array filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"SELF.age BETWEEN {10,15} AND SELF.name LIKE[cd] %@",@"tim*"]]);
    NSLog(@"filter1:%@",[array filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"SELF.age BETWEEN {10,15} AND SELF.name CONTAINS[cd] %@",@"tim"]]);
    NSLog(@"filter11:%@",[array filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"SELF.age BETWEEN {10,15} AND SELF.name CONTAINS[cd] %@",@"tim"]]);
    NSLog(@"filte2r:%@",[array filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"SELF.age >= 10 AND SELF.age <= 15"]]);
    NSLog(@"filter3:%@",[array filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(Model *evaluatedObject, NSDictionary<NSString *,id> * _Nullable bindings) {
        if (evaluatedObject.age >= 10 && evaluatedObject.age <= 15) {
            return YES;
        }
        return NO;
    }]]);
/*
filter0:(
    "<Model: 0x6000037f2780>"
)
filter00:(
    "<Model: 0x6000037f2780>"
)
filter1:(
    "<Model: 0x6000037f2780>"
)
 filter11:(
    "<Model: 0x6000037f2780>"
)
filte2r:(
    "<Model: 0x6000037f2720>",
    "<Model: 0x6000037f2780>"
) 
filter3:(
    "<Model: 0x6000037f2720>",
    "<Model: 0x6000037f2780>"
)
*/

谓词占位符

%K,%@
其中%K可以表示需要匹配的property,比如 name LIKE 'tim'，
用占位符表示为%K LIKE %@,@"name",@"tim"

比较运算

关键字

=、==
表示两个表达式或值是否相等，比如：

NSPredicate *predicate11 = [NSPredicate predicateWithFormat:@"SELF = 'abc'"];
NSPredicate *predicate12 = [NSPredicate predicateWithFormat:@"SELF ==[cd] 'abc'"];
NSLog(@"结果11:%d",[predicate11 evaluateWithObject:str]);
NSLog(@"结果12:%d",[predicate12 evaluateWithObject:str]);
//结果11:0
//结果12:1

>,<,>=,<=,!=
大小比较
BETWEEN
表示在范围区间之间，比如：SELF BETWEEN {100,200} 等价于 SELF >= 100 && SELF <= 200.

逻辑运算

AND,&&
逻辑与
OR,||
逻辑或
NOT,!
逻辑非

字符串匹配

关键字：

BEGINSWITH
以某个字符开头，比如：判断是否以w字符开头，BEGINSWITH 'w'
ENDSWITH
以某个字符结尾，比如：判断是否以w字符结尾，ENDSWITH 'w'
CONTAINS
表示字符串中是否包含某特定字符串，比如：CONTAINS 'abc'
LIKE
检测字符串是否匹配某字符串模板，比如：name LIKE '?a'。表示name是否为第二个字母为'a'
MATCHES
用于匹配正则表达式，比如匹配手机号等：SELF MATCHES '^[1][3-8]\d{9}$'
其中可以用[c]紧接在关键字后表示忽略大小写匹配，[d]表示忽略重低音匹配，[cd]可以一起连用。比如：

NSString *str = @"aBc";
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF CONTAINS[cd] 'b'"];
NSLog(@"结果:%d",[predicate evaluateWithObject:str]);
//结果:1

集合运算