NSPredicate 的用法举例

标签：nspredicate   谓词   cocoa   coredata   

Cocoa 提供了一个名为NSPredicate的类，用于指定过滤器的条件，用NSPredicate描述查询方式，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，常见的用于Core Data和Spotlight。 本文讲解过程中用到了部分类比如garage（车库的类），car（车）等仅供举例，未列出创建代码，体会predicate的用法才是关键。

创建Predicate.

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

计算Predicate

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"engine.horsepowe > 150"];
    NSArray *cars = [garage cars];
    for (Car *car in [garage cars]) {
        if ([predicate evaluateWithObject:car]) {
            NSLog(@"%@",car.name);
        }
    }

数组过滤器

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"engine.horsepowe > 150"];
    NSArray *results;
    results = [cars filteredArrayUsingPredicate:predicate];

    NSMutableArray *carsCopy = [cars mutableCopy];
    [carsCopy filterUsingPredicate:predicate];

构造灵活Predicate

有两种方式，

第一种 格式说明符

    NSPredicate *predicate1, *predicate2, *predicate3;
    
    predicate1 = [NSPredicate predicateWithFormat:@"engine.horsepowe > %d",50];
    
    predicate2 = [NSPredicate predicateWithFormat:@"name == %@",@"Herbie"];
    
    predicate3 = [NSPredicate predicateWithFormat:@"%k == %@", @"name", @"Herbie"];

    NSPredicate *predicateTemplate = [NSPredicate predicateWithFormat:@"name == $NAME"];
    
    NSDictionary *varDict;
    varDict = [NSDictionary dictionaryWithObjectsAndKeys:@"Herbie",@"NAME", nil];
    
    NSPredicate *predicate = [predicateTemplate predicateWithSubstitutionVariables:varDict];

    predicateTemplate = [NSPredicate predicateWithFormat:@"engine.horsepower > $POWER"];
    
    varDict = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:150], @"POWER", nil];
    
    predicate = [predicateTemplate predicateWithSubstitutionVariables:varDict];

predicate的运算符

支持C语言的常用运算符 ==    =    >    <    >=    <=   !=    <>   &&    ||   !   AND    OR   NOT等

    predicate = [NSPredicate predicateWithFormat:@"(engine.horsepower > 50) AND (engine.horsepower < 200)"];
    results = [cars filteredArrayUsingPredicate:predicate];

    predicate = [NSPredicate predicateWithFormat:@"engine.horsepower BETWEEN{50,200}"];

等价于

    NSArray *betweens = [NSArray arrayWithObjects:[NSNumber numberWithInt:50],[NSNumber numberWithInt:200],nil];
    predicate = [NSPredicate predicateWithFormat:@"engine.horsepower BEWEEN %@",betweens];

    predicate = [NSPredicate predicateWithFormat:@"SELF IN %@", names1];
    results = [names2 filteredArrayUsingPredicate:predicate];
    NSLog(@"%@", results);

(
  Judge,

  Badger

)

字符串运算符

BEGINSWITH       检查某个字符串是否以另一个字符串开头

ENDSWITH           检查某个字符串是否以另一个字符串结尾

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NSPredicate 的用法举例

标签：nspredicate   谓词   cocoa   coredata   

原文地址：http://blog.csdn.net/marvindev/article/details/41549459