2018-06-27 学习NSPredicate

一.概念

Cocoa提供一个名为NSPredicate的类，用于指定过滤器的条件。可以创建这个对象，通过该对象准确地描述所需的文件，对每个对象通过谓词进行筛选，判断它们是否与条件相匹配。

二.相关样例

Car *car1 = [[Car alloc] init];
[car1 setName: @"Hoben"];
[car1 setHorsePower: 160];

NSPredicate *predicate = [NSPredicate predicateWithFormat: @"name == 'Hoben'"];
BOOL match = [predicate evaluateWithObject: car1];
NSLog(@"%d", match);

NSPredicate *predicate = [NSPredicate predicateWithFormat: @"name == 'Hoben'"];
BOOL match = [predicate evaluateWithObject: car1];
NSLog(@"%d", match);

Car *car2 = [[Car alloc] init];
[car2 setName: @"JP"];
[car2 setHorsePower: 100];

Car *car3 = [[Car alloc] init];
[car3 setName: @"Road"];
[car3 setHorsePower: 200];

NSArray *cars = [[NSArray alloc] initWithObjects: car1, car2, car3, nil];

predicate = [NSPredicate predicateWithFormat: @"horsePower > 150"];
for (Car *car in cars) {
    BOOL matchPower = [predicate evaluateWithObject: car];
    if (matchPower)
        NSLog(@"%@", [car name]);
}

用另一个函数filteredArrayUsingPredicate替代for循环：

NSArray *results;
results = [cars filteredArrayUsingPredicate: predicate];
NSLog(@"%@", results);

以下两句等价：

predicate = [NSPredicate predicateWithFormat: @"horsePower > 150 && horsePower < 170"];
predicate = [NSPredicate predicateWithFormat: @"horsePower BETWEEN {150, 170}"];

使用IN：

predicate = [NSPredicate predicateWithFormat: @"Self.name IN {'Hoben', 'JP'}"];

字符串运算符

字符串运算符中，可以使用BEGINSWITH,CONTAINS,ENDSWITH，后加修饰符[cd]/[c]/[d]，分别代表：不区分大小写和发音、不区分大小写、不区分发音

predicate = [NSPredicate predicateWithFormat: @"Self.name BEGINSWITH[cd] 'Ho'"];
predicate = [NSPredicate predicateWithFormat: @"Self.name CONTAINS[c] 'ho'"];
predicate = [NSPredicate predicateWithFormat: @"Self.name ENDSWITH 'ben'"];

可以运用LIKE运算符，*ob*代表包含"ob"的字符串，*??be*代表be前面至少有两个字符。

predicate = [NSPredicate predicateWithFormat: @"Self.name LIKE '*ob*'"];
predicate = [NSPredicate predicateWithFormat: @"Self.name LIKE '*??be*'"];