无法在Objective-C中使用正则表达式

Question

由于某些原因，我无法使正则表达式适用于多行字符串。 在网路上运作良好

我有这样的文字：

    First Line //remove leading spaces
Second Line //nothing to remove
  Third Line //remove leading spaces
Fourth Line
should be 1 line //remove leading spaces and new line next char is not a capital letter

 Fifth line //remove leading spaces, keep new line between the two sentences 

我正在尝试使用此正则表达式

^ +|\b\n\b

在在线正则表达式编辑器（例如http://rubular.com/r/u4Ao5oqeBi ）中，它几乎可以正常工作（除非它删除了多余的新行）

但这只会删除第一行中的前导空格。这是我的代码：

        NSString *myText = @"    First Line (remove leading spaces\nSecond Line (nothing to remove\n  Third Line (remove leading spaces\n Fourth Line\nshould be 1 line (remove leading spaces and new line next char is not a capital letter\n\n Fifth line (remove leading spaces, keep new line between the two sentences";
        NSLog(myText);

        NSString *resultText = [myText stringByReplacingOccurrencesOfString: @"^ +|\\b\\n\\b"
                                                                 withString: @""
                                                                    options: NSRegularExpressionSearch
                                                                      range: NSMakeRange(0, myText.length)];

        NSLog(resultText);

Answer 1

您的代码不起作用，因为您使用的是stringByReplacingOccurrencesOfString ，并且target参数中使用了正则表达式字符串，而不是输入字符串。 它不接受正则表达式。 有关此功能，请参见《 基础框架参考》帮助。

您可以使用以下代码删除所有前导空格：

NSError *error = nil;
NSString *myText = @"    First Line (remove leading spaces\nSecond Line (nothing to remove\n  Third Line (remove leading spaces\n Fourth Line\nshould be 1 line (remove leading spaces and new line next char is not a capital letter\n\n Fifth line (remove leading spaces, keep new line between the two sentences";
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"^ +" options:NSRegularExpressionCaseInsensitive|NSRegularExpressionAnchorsMatchLines error:&error];
NSString *modifiedString = [regex stringByReplacingMatchesInString:myText options:0 range:NSMakeRange(0, [myText length]) withTemplate:@""];
NSLog(@"%@", modifiedString);

我正在使用NSRegularExpressionAnchorsMatchLines选项使^匹配行的开头，而不是整个字符串的开头（请参见此正则表达式元字符表）。 输出：

First Line (remove leading spaces                                                                                                                                                                                     
Second Line (nothing to remove                                                                                                                                                                                                                         
Third Line (remove leading spaces                                                                                                                                                                                                                      
Fourth Line                                                                                                                                                                                                                                            
should be 1 line (remove leading spaces and new line next char is not a capital letter                                                                                                                                                                 

Fifth line (remove leading spaces, keep new line between the two sentences