可以使用String类中的subString方法

String s = "one.two";

//Removes everything after first '.'
String result = s.substring(0, s.indexOf('.'));
print(result);

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如果String中有多个“.”，它将使用第一次出现的“.”。如果您需要使用最后一个“.”（例如，为了摆脱文件扩展名），请将indexOf更改为lastIndexOf。如果您不确定至少有一个“.”，则还应添加一些验证以避免触发异常。

String s = "one.two.three";

//Remove everything after last '.'
var pos = s.lastIndexOf('.');
String result = (pos != -1)? s.substring(0, pos): s;
print(result);

型

void main() {
  String str = "one.two";
  print(str.replaceAll(".two", ""));

  // or

  print(str.split(".").first);

  // or

  String newStr = str.replaceRange(str.indexOf("."), str.length, "");
  print(newStr);

  // Lets do a another example

  String nums = "1,one.2,two.3,three.4,four";
  List values = nums.split("."); // split() will split from . and gives new List with separated elements.
  values.forEach(print);

  //output

//   1,one
//   2,two
//   3,three
//   4,four
}

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在DartPad中编辑此内容。
实际上，在String中还有其他很酷的方法。看看那些here。

String str = "one.two";
var value = str?.replaceFirst(RegExp(r"\.[^]*"), "");

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如果确定str包含.，则可以使用str.substring(0, str.indexOf('.'));
否则，您将得到错误Value not in range: -1。

答案在上面，但这里是你如何做到这一点，如果你想只有某些字符的位置或位置。
为了从Dart String中获取子字符串，我们使用substring()方法：

String str = 'bezkoder.com';

// For example, here we want ‘r’ is the ending. In ‘bezkoder.com’,
// the index of ‘r’ is 7. So we need to set endIndex by 8.
str.substring(0,8); // bezkoder

str.substring(2,8); // zkoder
str.substring(3);   // koder.com

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这是返回String的substring()方法的签名：

String substring(int startIndex, [int endIndex]);

型
startIndex：开始字符的索引。开始索引为0。endIndex（可选）：结束字符的索引+ 1。如果不设置，结果将是从startIndex开始到字符串结尾的减法。
[参考] [1]：https://bezkoder.com/dart-string-methods-operators-examples/

String str = "one.two";
  print(str.replaceAll(".two", ""));

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这里是一个完整的工作代码，结合了所有上述解决方案
也许我的语法编写和分割代码是不常见的，，对不起，我自学初学者

// === === === === === === === === === === === === === === === === === === ===
import 'dart:io';
import 'package:flutter/services.dart';
import 'package:path_provider/path_provider.dart';

/// in case you are saving assets in flutter project folder directory like this
/// 'assets/xyz/somFolder/image.jpg'
/// And u have a separate class where u save assets in variables like this to easily call them in your widget tree
/// 
/// class SuperDuperAsset {
///   static const String DumAuthorPic = 'assets/dum/dum_author_pic.jpg' ;
///   static const String DumBusinessLogo = 'assets/dum/dum_business_logo.jpg' ;
///   }
///   
/// I just want to insert SuperDuperAsset.DumBusinessLogo in this function below
/// 
/// and here is a fix and a combination for all mentioned solutions that works like a charm in case you would like to copy paste it
/// and just use this function like this
/// 
/// File _imageFile = await getImageFileFromAssets(SuperDuperAsset.DumBusinessLogo);
/// and you are good to go
/// 
/// some other functions that manipulate the asset path are separated below
Future<File> getImageFileFromAssets(String asset) async {
  
  String _pathTrimmed = removeNumberOfCharacterFromAString(asset, 7);
  
  final _byteData = await rootBundle.load('assets/$_pathTrimmed');
  
  final _tempFile = File('${(await getTemporaryDirectory()).path}/${getFileNameFromAsset(_pathTrimmed)}');
  
  await _tempFile.writeAsBytes(_byteData.buffer.asUint8List(_byteData.offsetInBytes, _byteData.lengthInBytes));
  
  _tempFile.create(recursive: true);
  
  return _tempFile;

}
// === === === === === === === === === === === === === === === === === === ===
String removeNumberOfCharacterFromAString(String string, int numberOfCharacters){
  String _stringTrimmed;
  if (numberOfCharacters > string.length){
    print('can not remove ($numberOfCharacters) from the given string because : numberOfCharacters > string.length');
    throw('can not remove ($numberOfCharacters) from the given string because');
  } else {
    _stringTrimmed = string.length >0 ? string?.substring(numberOfCharacters) : null;
  }
  return _stringTrimmed;
}
// === === === === === === === === === === === === === === === === === === ===
/// this trims paths like
/// 'assets/dum/dum_business_logo.jpg' to 'dum_business_logo.jpg'
String getFileNameFromAsset(String asset){
  String _fileName = trimTextBeforeLastSpecialCharacter(asset, '/');
  return _fileName;
}
// === === === === === === === === === === === === === === === === === === ===
String trimTextBeforeLastSpecialCharacter(String verse, String specialCharacter){
  int _position = verse.lastIndexOf(specialCharacter);
  String _result = (_position != -1)? verse.substring(_position+1, verse.length): verse;
  return _result;
}
// === === === === === === === === === === === === === === === === === === ===

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var regex = RegExp(r'.[a-z]*$');
String s='one.two';
print(s.replaceAll(regex,''));

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