無法在Objective-C中進行正則表達式工作

Question

出於某種原因，我無法使正則表達式適用於多行字符串。它工作正常，網絡上

我有這樣的文字：

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 

我試圖用這個表達式

^ +|\b\n\b 

它的工作原理幾乎罰款（除非它消除更多的新線路在線正則表達式編輯器，如http://rubular.com/r/u4Ao5oqeBi

但它只是從第一行刪除前導空間 這是我的代碼：

 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

，因爲你正在使用stringByReplacingOccurrencesOfString與在target論點，而不是輸入字符串正則表達式的字符串代碼不工作。它不接受正則表達式。請參閱Foundation Framework Reference關於此功能的幫助。

您可以使用下面的代碼刪除所有前導空格：

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); 

我使用NSRegularExpressionAnchorsMatchLines選項，以使^匹配行的開始，整個字符串並非一開始（見本Regular Expressions Metacharacters表）。 輸出：

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