“全字”通过NSPredicate在NSString中搜索 [英] "Whole word" search in a NSString through NSPredicate

问题描述

我想搜索是否在属性 description （一个 NSString 实例）中有一个给定的单词。

我尝试使用此谓词：

  [NSPredicate predicateWithFormat：@ description CONTAINS [cd]％@，theWord]; 
  

它可以工作，但也会找到子字。

例如，给定 theWord ：

汽车

它也会

圣诞颂歌

我的谓词只匹配 a 或 christmas 或 carol 。

（我使用Core Data和NSFetchRequest。）

解决方案>

这样的东西吗？

  NSString * matchStr = @。* \\bCarol\\b 。*; 
 
 NSPredicate * pred = [NSPredicate predicateWithFormat：@description MATCHES％@，matchStr]; 
 
 NSArray * arr = @ [
 @A Christmas Carol，
 @Sing，
 @Song
] 
 
 NSArray * filtered = [arr filteredArrayUsingPredicate：pred]; 
  

窍门是 \b 元字符，其表示字符串中的字边界。为了得到一个反斜杠into正则表达式模式字符串，你必须在它之前有另一个反斜杠，所以编译器理解在字符串中应该有一个真正的反斜杠。因此，字符串中的\\b。

此外，为了更好地覆盖非英语字符串，您应该启用Unicode字边界检测，设置 w 标志选项。匹配字符串将如下所示：

  NSString * matchStr = @（？w）。* \\bCarol\\ \\\b。*; 
  

I would like to search if in the attribute description (an NSString instance) there is a given word.

I tried with this predicate:

[NSPredicate predicateWithFormat:@"description CONTAINS[cd] %@", theWord];

It works, but it finds also sub-words.

For example, given theWord:

Car

it will mach also this description:

A Christmas Carol

Instead, I would like that my predicate will match only a, or christmas, or carol.

(I'm using Core Data and NSFetchRequest.)

解决方案

Something like this?

NSString *matchStr = @".*\\bCarol\\b.*";

NSPredicate *pred =[NSPredicate predicateWithFormat: @"description MATCHES %@", matchStr];

NSArray *arr = @[ 
    @"A Christmas Carol",
    @"Sing",
    @"Song"
];

NSArray *filtered = [arr filteredArrayUsingPredicate: pred];

The trick is the \b metacharacter, which denotes a word boundary in the string. In order to get a backslash "into" the regex pattern string, you have to precede it with another backslash so the compiler understands that there should be a real backslash in the string. Hence the "\\b" in the string.

Also, in order to cover non-English language strings better, you should enable Unicode word boundary detection, by setting the w flag option. The match string will look like this:

NSString *matchStr = @"(?w).*\\bCarol\\b.*"; 

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