無法在Objective-C中使用正則表達式

Question

由於某些原因，我無法使正則表達式適用於多行字符串。 在網路上運作良好

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 

我正在嘗試使用此正則表達式

^ +|\b\n\b

在在線正則表達式編輯器（例如http://rubular.com/r/u4Ao5oqeBi ）中，它幾乎可以正常工作（除非它刪除了多余的新行）

但這只會刪除第一行中的前導空格。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

您的代碼不起作用，因為您使用的是stringByReplacingOccurrencesOfString ，並且target參數中使用了正則表達式字符串，而不是輸入字符串。 它不接受正則表達式。 有關此功能，請參見《 基礎框架參考》幫助。

您可以使用以下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);

我正在使用NSRegularExpressionAnchorsMatchLines選項使^匹配行的開頭，而不是整個字符串的開頭（請參見此正則表達式元字符表）。 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