如果您使用get: ^4.6.5作为flutter的状态管理，则有用于大写的内置扩展

        // This will capitalize first letter of every word
        print('hello world'.capitalize); // Hello World

        // This will capitalize first letter of sentence
        print('hello world'.capitalizeFirst); // Hello world

        // This will remove all white spaces from sentence
        print('hello world'.removeAllWhitespace); // helloworld

        // This will convert string to lowerCamelCase
        print('This is new world'.camelCase); // thisIsNewWorld

        // This will remove all white spaces between the two words and replace it with '-'
        print('This is new    world'.paramCase); // this-is-new-world

奇怪的是，这是不可用的dart开始。下面是一个扩展的大写字符串:

extension StringExtension on String {
  String capitalized() {
    if (this.isEmpty) return this;
    return this[0].toUpperCase() + this.substring(1);
  }
}

它首先检查String是否为空，然后将第一个字母大写，并将其余字母相加

用法:

import "path/to/extension/string_extension_file_name.dart";

var capitalizedString = '${'alexander'.capitalized()} ${'hamilton, my name is'.capitalized()} ${'alexander'.capitalized()} ${'hamilton'.capitalized()}');
// Print result: "Alexander Hamilton, my name is Alexander Hamilton"

我使用了不同的实现:

创建一个类:

import 'package:flutter/services.dart';

class FirstLetterTextFormatter extends TextInputFormatter {
  @override
  TextEditingValue formatEditUpdate(
      TextEditingValue oldValue, TextEditingValue newValue) {
    return TextEditingValue(
      //text: newValue.text?.toUpperCase(),
      text: normaliseName(newValue.text),
      selection: newValue.selection,
    );
  }

  /// Fixes name cases; Capitalizes Each Word.
  String normaliseName(String name) {
    final stringBuffer = StringBuffer();

    var capitalizeNext = true;
    for (final letter in name.toLowerCase().codeUnits) {
      // UTF-16: A-Z => 65-90, a-z => 97-122.
      if (capitalizeNext && letter >= 97 && letter <= 122) {
        stringBuffer.writeCharCode(letter - 32);
        capitalizeNext = false;
      } else {
        // UTF-16: 32 == space, 46 == period
        if (letter == 32 || letter == 46) capitalizeNext = true;
        stringBuffer.writeCharCode(letter);
      }
    }

    return stringBuffer.toString();
  }
}

然后你导入类到任何页面，你需要例如在TextField的inputFormatters属性，只是调用上面的小部件:

TextField(
inputformatters: [FirstLetterTextFormatter()]),
),

String fullNameString =
    txtControllerName.value.text.trim().substring(0, 1).toUpperCase() +
        txtControllerName.value.text.trim().substring(1).toLowerCase();

最简单的答案是:

首先使用下标将字符串的第一个字母大写，然后将字符串的其余部分拼接起来。

这里username是字符串。

用户名[0].toUpperCase（） + username.substring（1）;

你可以用这个:

extension EasyString on String {
  String toCapitalCase() {
   var lowerCased = this.toLowerCase();
   return lowerCased[0].toUpperCase() + lowerCased.substring(1);
 }
}