“无效的谓词：nil RHS” NSPredicate格式的第二个参数 [英] "Invalid predicate: nil RHS" for second argument in NSPredicate format

问题描述

这是我的 NSPredicate ：

print(searchTextField.text!)
let predicate = NSPredicate(format: "student.schoolClass.id = %d AND (book.title CONTAINS[cd] %@ OR student.username CONTAINS[cd] %@)", currentSchoolClass.id, searchTextField.text!, searchTextField.text!)

我接下来要做的是：

fetchedResultsController.fetchRequest.predicate = predicate
print(fetchedResultsController.fetchRequest.predicate!)
try! fetchedResultsController.performFetch() //here is the crash

控制台输出是：

j  
student.schoolClass.id == 1 AND (book.title CONTAINS[cd] nil OR student.username CONTAINS[cd] "j")

崩溃信息是：

CRASH: Invalid predicate: nil RHS

Isn'这很奇怪吗？

Isn't it weird?

推荐答案

在所有当前的iOS和OS X平台上，C int 是一个32位整数，
，这是变量参数列表中％d 格式所期望的。
如果传递一个64位整数，那么读取下一个变量参数
将读取额外的4个零字节。

On all current iOS and OS X platforms, the C int is a 32-bit integer, and that is what the %d format expects on the variable argument list. If you pass a 64-bit integer then reading the next variable argument will read the extra 4 zero bytes.

下表显示哪个格式是针对哪个整数类型：

The following table shows which format is for which integer type:

  Format   C type          Swift type
  -----------------------------------
  %d       int             Int32
  %ld      long int        Int
  %lld     long long int   Int64

以及类似的无符号类型。

and similarly for the unsigned types.

或者，将整数转换为一个 NSNumber 对象并使用
％@ 格式，对于所有整数，这都是
大小。示例：

Alternatively, convert the integer to a NSNumber object and use the %@ format, this works for integers of all sizes. Example:

let value = 1234
let predicate = NSPredicate(format: "value = %@", value as NSNumber)

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