ios 如何在 Core Data 中编写 BOOL 谓词？
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How to write a BOOL predicate in Core Data?
提问by Proud Member
I have an attribute of type BOOLand I want to perform a search for all managed objects where this attribute is YES.
我有一个 type 属性，BOOL我想搜索此属性所在的所有托管对象YES。
For string attributes it is straightforward. I create a predicate like this:
对于字符串属性，它很简单。我创建了一个这样的谓词：
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"userName = %@", userName];
But how do I do this, if I have a bool attribute called selectedand I want to make a predicate for this? Could I just do something like this?
但是，如果我有一个名为selected的 bool 属性并且我想为此做一个谓词，我该怎么做？我可以做这样的事情吗？
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"selected = %@", yesNumber];
Or do I need other format specifiers and just pass YES?
或者我是否需要其他格式说明符并通过YES？
回答by albertamg
From Predicate Programming Guide:
从谓词编程指南：
You specify and test for equality of Boolean values as illustrated in the following examples:
您指定并测试布尔值是否相等，如以下示例所示：
NSPredicate *newPredicate = [NSPredicate predicateWithFormat:@"anAttribute == %@", [NSNumber numberWithBool:aBool]];
NSPredicate *testForTrue = [NSPredicate predicateWithFormat:@"anAttribute == YES"];
You can also check out the Predicate Format String Syntax.
回答by Viktor Kucera
Swift 4.0
斯威夫特 4.0
let predicate = NSPredicate(format: "boolAttribute == %@", NSNumber(value: true))
回答by alegelos
Don't convert to NSNumber, nor use double "=="
不要转换为 NSNumber，也不要使用双 "=="
More appropriate for Swift >= 4:
更适合 Swift >= 4：
NSPredicate(format: "boolAttribute = %d", true)
Note: "true" in this example is a Bool (a Struct)
注意：本例中的“true”是一个 Bool（一个结构体）
回答by Lukas Kukacka
Swift 3
斯威夫特 3
let predicate = NSPredicate(format: "boolAttribute == %@", NSNumber(value: true))
In Swift 3 you should use NSNumber(value: true).
在 Swift 3 中，您应该使用NSNumber(value: true).
Using NSNumber(booleanLiteral: true)and in general any literal initialiser directly is discouraged and for example SwiftLint(v. 0.16.1) will generate warning for usage ExpressibleBy...Literalinitialiser directly:
NSNumber(booleanLiteral: true)通常不鼓励直接使用任何文字初始化器，例如SwiftLint(v. 0.16.1) 将ExpressibleBy...Literal直接为使用初始化器生成警告：
Compiler Protocol Init Violation: The initializers declared in compiler protocols such as
ExpressibleByArrayLiteralshouldn't be called directly. (compiler_protocol_init)
编译器协议初始化违规：在编译器协议中声明的初始化程序
ExpressibleByArrayLiteral不应直接调用。(compiler_protocol_init)
回答by SoftDesigner
Swift 4
斯威夫特 4
request.predicate = NSPredicate(format: "boolAttribute == %@", NSNumber(value: true))
Swift 3
斯威夫特 3
request.predicate = NSPredicate(format: "field = %@", value as CVarArg)
回答by Mario Hendricks
Swift 3.0has made a slight change to this:
Swift 3.0对此略有改动：
let predicate = NSPredicate(format: "boolAttribute == %@", NSNumber(booleanLiteral: true))
