谓词

过滤数组中的字符串

    NSArray *arr = @[@"hello",@"world",@"wellcome"];
    //创建一个谓词,谓词的逻辑是被过滤的主体是以'h'开头 的字符串
    //self 代表对象自身, like为指定搜索模式, '*'为通配符
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"self like h*"];
    predicate = [NSPredicate predicateWithFormat:@"self beginswith 'h'"];    
    //筛选以'd'结尾
    predicate = [NSPredicate predicateWithFormat:@"self endswith 'd'"];
    predicate = [NSPredicate predicateWithFormat:@"self like '*d'"];
    //将数组中所有满足条件的筛选出来, 生成新的数组
    NSArray *result = [arr filteredArrayUsingPredicate:predicate];
    //筛选含有'h'的单词
    //[c]指定不区分大小写
    predicate = [NSPredicate predicateWithFormat:@"self contains[c] 'h'"];
    predicate = [NSPredicate predicateWithFormat:@"self like *h*"];

判断对象是否符合某种条件

    NSString *demoStr = @"hello world!!";
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"self like h*"];
    BOOL isBeginWith_h = [predicate evaluateWithObject:demoStr];

过滤自定义对象的实例变量符合某种条件

    Person *person1 = [[Person alloc] initWithName:@"张三" andAge:21];
    Person *person2 = [[Person alloc] initWithName:@"李四" andAge:22];
    Person *person3 = [[Person alloc] initWithName:@"王五" andAge:23];
    Person *person4 = [[Person alloc] initWithName:@"赵六" andAge:24];
    NSArray *arr = @[person1,person2,person3,person4];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name contains '三'"];
    NSArray *result = [arr filteredArrayUsingPredicate:predicate];
    for (Person *tmp in result) {
        NSLog(@"---------->%@:%ld",tmp.name,tmp.age);
    }
    
    NSPredicate *predicate2 = [NSPredicate predicateWithFormat:@"age >= 22 && age < 24"];
    result = [arr filteredArrayUsingPredicate:predicate2];
    for (Person *tmp in result) {
        NSLog(@"----->%@:%ld",tmp.name,tmp.age);
    }

匹配正则表达式

 NSPredicate *predicate = [NSPredicate predicateWithFormat:@"self matches %@", @"正则表达式"];