ios - 谓词为零，nscoredata，目标

Question

我正在做的是获取核心数据的数据如下

NSString *str;
NSPredicate *predicate;

switch (typeCube) {
    case NewCubes: {
        str = [NSString stringWithFormat:@"type == %d",NewCubes];
        break;
    }
    case AllCubes: {
        str = [NSString stringWithFormat:@"type != %d",CustomCubes];
        break;
    }
    case CustomCubes: {
        str = [NSString stringWithFormat:@"type == %d",CustomCubes];
        break;

    }
}

predicate = [NSPredicate predicateWithFormat:@"%@ AND (accounts.keyChainId == %@)", str, accountKeyChainId];

但是，predicate 的结果是 nil。但是下面的作品

predicate = [NSPredicate predicateWithFormat:@"(type == %d) AND (accounts.keyChainId == %@)", type, accountKeyChainId]; ( type is either NewCubes or AllCubes or CustomCubes)

如果您有任何想法，请提供帮助。欢迎所有评论。谢谢

Answer 1

有一个名为 NSCompoundPredicate 的类，它允许您使用 AND、OR 和 NOT 运算符构造谓词。这里需要

[NSCompoundPredicate andPredicateWithSubpredicates:@[predicate1, predicate2, etc.]];

所以代码将是——

NSPredicate *predicate1;
NSPredicate *predicate;

    switch (typeCube) {
        case NewCubes: {
            predicate1 = [NSPredicate predicateWithFormat:@"type == %d",NewCubes];
            break;
        }
        case AllCubes: {
            predicate1 = [NSPredicate predicateWithFormat:@"type != %d",CustomCubes];
            break;
        }
        case CustomCubes: {
            predicate1 = [NSPredicate predicateWithFormat:@"type == %d",CustomCubes];
            break;

        }
    }
    predicate = [NSPredicate predicateWithFormat:@"accounts.keyChainId == %@", accountKeyChainId];
    [NSCompoundPredicate andPredicateWithSubpredicates:@[predicate1, predicate]];

在这里阅读更多关于 NSCompountPredicates 的信息:http://nshipster.com/nspredicate/