在特定索引处替换：

由于dart中的String是不可变的refer，因此我们无法编辑如下内容

stringInstance.setCharAt(index, newChar)

满足要求的有效方法为：

String hello = "hello";
String hEllo = hello.substring(0, 1) + "E" + hello.substring(2);
print(hEllo); // prints hEllo

进入函数：

String replaceCharAt(String oldString, int index, String newChar) {
  return oldString.substring(0, index) + newChar + oldString.substring(index + 1);
}
replaceCharAt("hello", 1, "E") //usage

• 注意：上述函数中的 * index是 * 从零开始的 *。

您可以使用replaceFirst()。

final myString = 'hello hello';
final replaced = myString.replaceFirst(RegExp('e'), '*');  // h*llo hello

或者，如果你不想替换第一个，你可以使用一个开始索引：

final myString = 'hello hello';
final startIndex = 2;
final replaced = myString.replaceFirst(RegExp('e'), '*', startIndex);  // hello h*llo

您可以使用replaceAll（）。

String string = 'string';
final letter='i';
final newLetter='a';
string = string.replaceAll(letter, newLetter);  // strang

使用此行，您可以将$符号替换为空格''

'${double.parse (_priced.toString (). replaceAll (' \ $ ',' ')) ?? '\ $ 0.00'}'

String x = _with.price.toString (). ReplaceAll ('\ $', '')) ?? '\ $ 0.00',

您可以在构建函数中使用它来完成此操作。

s.replaceRange(start, end, newString)

以下是您可以执行的操作

final singleChar = 'a';
  final characters = yourString.characters.toList();
  characters[index] = singleChar;
  yourString = characters.join('');

下面是它在String扩展方法中的样子

String replaceCharAt({required String char, required int index}) {
    final chars = characters.toList();
    chars[index] = char;
    return chars.join('');
  }

你可以使用这个函数，只是修改了Dinesh的答案

String _replaceCharAt(
          {required String character,
          required int index,
          required String oldString}) {
        if (oldString.isEmpty) {
          return character;
        } else if (index == oldString.length) {
          return oldString.substring(0, index) + character;
        } else if (index > oldString.length) {
          throw RangeError('index value is out of range');
        }
    
        return oldString.substring(0, index) +
            character +
            oldString.substring(index + 1);
      }

你也可以使用子字符串而不用担心字符，从字符串创建子字符串并使用索引。

String ourString = "OK_AY"; // original string - length of 5
String oldChar = "_"; // the character we wanna find and replace - as type string - in this case, an underscore
String newChar = "X" // the char we wanna replace underscore with
int index = ourString.indexOf(oldChar, 0); // find the index in string where our char exists (may not exist)

//some logic here to return or skip next code if char wasn't found

//oldChar found at index 0 (beginning of string)
if (index == 0) {
    ourString = newChar + ourString.substring(index+1, ourString.length);
}

//oldChar found at index 4 (end of string)
else if (index == str.length-1) {
      ourString = ourString.substring(0, index) + newChar;
}

//oldChar found anywhere else between
else {
      ourString = ourString.substring(0, index) + newChar + ourString.substring(index+1, ourString.length);
}

//done, ourString is now updated "OKXAY"