如何在 Dart 中创建私有变量? [英] How to create private variables in Dart?

问题描述

我想创建一个私有变量，但我不能.

这是我的代码:

void main() {var b = new B();b.testB();}A类{int_private = 0;测试A(){print('int 值:$_private');_私人 = 5;}}B 类扩展 A {字符串_私有；测试B(){_private = '你好';print('字符串值:$_private');测试A();print('字符串值:$_private');}}

当我运行这段代码时，我得到以下结果:

字符串值:你好整数值:你好打破异常:int"类型不是value"的String"类型的子类型.

我在编辑此源代码时也没有收到任何错误或警告.

如何在 Dart 中创建私有变量?

解决方案

来自 Dart 文档:

<块引用>

与 Java 不同，Dart 没有关键字 public、protected 和 private.如果标识符以下划线 _ 开头，则它对其库是私有的.

库不仅提供 API，而且是一个隐私单元:以下划线开头的标识符 _ 仅在库内部可见.

关于图书馆的几句话:

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每个 Dart 应用程序都是一个库，即使它不使用库指令.import 和 library 指令可以帮助您创建模块化和可共享的代码库.

您可能听说过 part 指令，它允许您将一个库拆分为多个 Dart 文件.

I want to create a private variable but I cannot.

Here is my code:

void main() {
  var b = new B();
  b.testB();    
}

class A {
  int _private = 0;

  testA() {
    print('int value: $_private');
    _private = 5;
  }
}

class B extends A {
  String _private;

  testB() {
    _private = 'Hello';
    print('String value: $_private');
    testA();
    print('String value: $_private');
  }
}

When I run this code, I get the following result:

String value: Hello
int value: Hello
Breaking on exception: type 'int' is not a subtype of type 'String' of 'value'.

Also I not get any error or warnings when editing this source code.

How can I create a private variable in Dart?

解决方案

From Dart documentation:

Unlike Java, Dart doesn’t have the keywords public, protected, and private. If an identifier starts with an underscore _, it’s private to its library.

Libraries not only provide APIs, but are a unit of privacy: identifiers that start with an underscore _ are visible only inside the library.

A few words about libraries:

Every Dart app is a library, even if it doesn’t use a library directive. The import and library directives can help you create a modular and shareable code base.

You may have heard of the part directive, which allows you to split a library into multiple Dart files.

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