NSPredicate

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第一次接触“谓词”是在大学课堂的《离散数学》里。当时觉得挺好，挺有用。从当时的阅历来看，找不到谓词的使用场景。

在开发中有很多地方可以使用谓词。谓词最基本的功能就是：if 语句的判断

第二功能：数据筛选

说了这么多，可能还是有人不懂，何为谓词；谓词的另一叫法：断定。

“今天下雨” 这是一句话对于这句话有两个可能的结果下雨或者不下。如果下雨，说明断定是对的，否则，断定是错的。

对于谓词，你可以简单的理解为：一个结果是BOOL的判定语句。

在实际的项目开发中，谓词的用途无外乎以上两种：作为if的条件、数据晒攒

看一下iOS中如何使用谓词

@interface Person : NSObject//定义一个Person类，头文件如下

@property(nonatomic,copy)NSString *name;

@property(nonatomic,assign)int age;

@property(nonatomic,copy)NSString *gender;

@property(nonatomic,assign)float score;

- (id)initWithName:(NSString *)name age:(int)age gender:(NSString *)gender score:(float)score;

+ (id)personWithName:(NSString *)name age:(int)age gender:(NSString *)gender score:(float)score;

@end

//在你的main或者某类的实现文件里添加两个方法

- (void)initPersonData//往数组里面添加若干Person对象

{

Person *p1 = [Person personWithName:@"张三" age:20 gender:@"男" score:89];

Person *p2 = [Person personWithName:@"李四" age:24 gender:@"男" score:65];

Person *p3 = [Person personWithName:@"王五" age:30 gender:@"男" score:76];

Person *p4 = [Person personWithName:@"小红" age:20 gender:@"女" score:92];

Person *p5 = [Person personWithName:@"小强" age:22 gender:@"女" score:62];

Person *p6 = [Person personWithName:@"小马哥" age:25 gender:@"男" score:87];

Person *p7 = [PersonpersonWithName:@"steve jobs"age:56gender:@"男"score:60];

Person *p8 = [PersonpersonWithName:@"neal"age:26gender:@"男"score:90];

self.persons = [[[NSMutableArrayalloc] initWithCapacity:8] autorelease];

[self.persons addObject:p1];

[self.persons addObject:p2];

[self.persons addObject:p3];

[self.persons addObject:p4];

[self.persons addObject:p5];

[self.persons addObject:p6];

[self.persons addObject:p7];

[self.persons addObject:p8];

}

- (void)predicateSimpleUse//谓词的测试

{

Person *p = [self.persons objectAtIndex:0];

//person的 name 是否是张三 name是person的属性注意： =和==是一样的

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name = '张三'"];

BOOL match = [predicate evaluateWithObject:p];

NSLog(@"%@",match?@"YES":@"NO");

//person的score是否 >= 90

predicate = [NSPredicate predicateWithFormat:@"score >= 90"];

for(Person *person in self.persons)

{

if([predicate evaluateWithObject:person])

{

NSLog(@"person:%@ %g",person.name,person.score);

}

//筛选出 score >= 90的所有person放入新的数组中对于NSMutableArray，还有个filterUsingPredicate:方法，原数组中筛选符合条件的元素

NSArray *results = [self.persons filteredArrayUsingPredicate:predicate];

NSLog(@"%@",results);

//含有变量的谓词

predicate = [NSPredicate predicateWithFormat:@"age = $Test"];

NSDictionary *dic = [NSDictionarydictionaryWithObjectsAndKeys:[NSNumbernumberWithInt:24],@"Test", nil];

NSPredicate *newPre = [predicate predicateWithSubstitutionVariables:dic];

NSLog(@"new %@",newPre);

for(Person *person in self.persons)

{

if([newPre evaluateWithObject:person])

{

NSLog(@"person:%@ %d",person.name,person.age);

}

NSLog(@"\n");

//谓词还支持C语言中的一些常用运算符

predicate = [NSPredicatepredicateWithFormat:@"age > 20 AND age < 26"];

for(Person *person in self.persons)

{

if([predicate evaluateWithObject:person])

{

NSLog(@"person:%@ %d",person.name,person.age);

}

predicate = [NSPredicate predicateWithFormat:@"name < 'zhang'"];

for(Person *person in self.persons)

{

if([predicate evaluateWithObject:person])

{

NSLog(@"person:%@",person.name);

}

predicate = [NSPredicatepredicateWithFormat:@"score between{60,80}"];

for(Person *person in self.persons)

{

if([predicate evaluateWithObject:person])

{

NSLog(@"person:%@ %g",person.name,person.score);

}

NSArray *betweens = [NSArrayarrayWithObjects:[NSNumbernumberWithFloat:60],[NSNumbernumberWithFloat:80], nil];

predicate = [NSPredicate predicateWithFormat:@"score between %@",betweens];

for(Person *person in self.persons)

{

if([predicate evaluateWithObject:person])

{

NSLog(@"person:%@ %g",person.name,person.score);

}

predicate = [NSPredicatepredicateWithFormat: @"name IN { '张三', '李四', '王五', '赵大' }"];

for(Person *person in self.persons)

{

if([predicate evaluateWithObject:person])

{

NSLog(@"person:%@ ",person.name);

}

//self可以出现在谓词里指的是使用谓词进行判定的对象

predicate = [NSPredicatepredicateWithFormat: @"self.name IN { '张三', '李四', '王五', '赵大' }"];

for(Person *person in self.persons)

{

if([predicate evaluateWithObject:person])

{

NSLog(@"person:%@ ",person.name);

}

//BEGINSWITH,ENDSWITH,CONTAINS

//附加符号，[c],[d],[cd],c表示不区分大小写，d表示不区分发音字符，cd表示什么都不区分

//beginswith

NSMutableArray *array =[NSMutableArrayarrayWithObjects:@"Nick", @"Ben", @"Adam", @"Melissa", nil];

NSPredicate *bPredicate = [NSPredicatepredicateWithFormat:@"SELF beginswith[c] 'a'"];

NSArray *beginWithB = [array filteredArrayUsingPredicate:bPredicate];

NSLog(@"%@",beginWithB);

//contains

NSPredicate *sPredicate = [NSPredicate predicateWithFormat:@"SELF contains[c] 'e'"];

[array filterUsingPredicate:sPredicate];

NSLog(@"array = %@",array);

//like运算符支持通配符? * ?表示1个字符 *表示若干字符

predicate = [NSPredicatepredicateWithFormat:@"name like [cd] '小*'"];

for(Person *person in self.persons)

{

if([predicate evaluateWithObject:person])

{

NSLog(@"person:%@ ",person.name);

}

//谓词支持正则表达式支持 keyPath

//想要更多了解谓词语法 Documents中搜索Predicate format string syntax

//想要更多了解谓词的使用 Documents中搜索using predicate

}

以下是调用的代码

[selfinitPersonData];

[selfpredicateSimpleUse];

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