# 定位到目标 widget > 如何在 widget 测试中使用 Finder 类。 To locate widgets in a test environment, use the [`Finder`][] classes. While it's possible to write your own `Finder` classes, it's generally more convenient to locate widgets using the tools provided by the [`flutter_test`][] package. 在测试环境下，为了定位 widgets，我们需要用到 [`Finder`][] 类。 我们可以编写自己的 `finder` 类， 不过通常使用 [`flutter_test`][] package 提供的工具来定位 widgets 更加方便。 During a `flutter run` session on a widget test, you can also interactively tap parts of the screen for the Flutter tool to print the suggested `Finder`. 运行 widget 测试，在执行 `flutter run` 的时候，你还可以与屏幕进行交互点击， Flutter 工具会输出建议的 `Finder`。 This recipe looks at the [`find`][] constant provided by the `flutter_test` package, and demonstrates how to work with some of the `Finders` it provides. For a full list of available finders, see the [`CommonFinders` documentation][]. 下面，我们来看看 `flutter_test` package 提供的 [`find`][] 常量并演示如何使用其所提供的 `Finders`。 如需查看完整的 finders 的列表， 请参阅 [`CommonFinders` 文档][`CommonFinders` documentation]。 If you're unfamiliar with widget testing and the role of `Finder` classes, review the [Introduction to widget testing][] recipe. 如果你还不熟悉 Widget 测试和 Finder 类使用方法， 请参阅 [Widget 测试介绍][Introduction to widget testing]。 This recipe uses the following steps: 本教程包含以下步骤： 1. Find a `Text` widget. 查找 `Text` Widget 2. Find a widget with a specific `Key`. 使用具体 `Key` 查找 Widget 3. Find a specific widget instance. 查找具体的 Widget 实例 ## 1. Find a `Text` widget ## 一. 查找 `Text` widget In testing, you often need to find widgets that contain specific text. This is exactly what the `find.text()` method is for. It creates a `Finder` that searches for widgets that display a specific `String` of text. 在测试中，我们经常需要查找含有特定文本的 widget。 这正是 `find.text()` 的用途。它会创建一个 `Finder` 来寻找显示特定文本 `String` 的 widget。 ```dart testWidgets('finds a Text widget', (tester) async { // Build an App with a Text widget that displays the letter 'H'. await tester.pumpWidget(const MaterialApp(home: Scaffold(body: Text('H')))); // Find a widget that displays the letter 'H'. expect(find.text('H'), findsOneWidget); }); ``` ## 2. Find a widget with a specific `Key` ## 二. 使用具体 `Key` 查找 widget In some cases, you might want to find a widget based on the Key that has been provided to it. This can be handy if displaying multiple instances of the same widget. For example, a `ListView` might display several `Text` widgets that contain the same text. 有时，我们可能想要通过已经提供给 widget 的 Key 来查找 widget。 这样在显示多个相同 widget 实体时会很方便。 比如，我们有一个 `ListView` 列表， 它显示了数个含有相同文本的 `Text` widgets。 In this case, provide a `Key` to each widget in the list. This allows an app to uniquely identify a specific widget, making it easier to find the widget in the test environment. 在这种情况下，我们可以为列表中的每一个 widget 赋予一个 `Key`。 这样我们就可以唯一识别特定的 widget， 在测试环境中更容易查找 widget。 ```dart testWidgets('finds a widget using a Key', (tester) async { // Define the test key. const testKey = Key('K'); // Build a MaterialApp with the testKey. await tester.pumpWidget(MaterialApp(key: testKey, home: Container())); // Find the MaterialApp widget using the testKey. expect(find.byKey(testKey), findsOneWidget); }); ``` ## 3. Find a specific widget instance ## 三. 查找具体的 Widget 实例 Finally, you might be interested in locating a specific instance of a widget. For example, this can be useful when creating widgets that take a `child` property and you want to ensure you're rendering the `child` widget. 最后，我们有时会需要查找 widget 的具体实例。 比如，当创建含有 `child` 属性的 widget 并需要确保渲染 `child` widget。 ```dart testWidgets('finds a specific instance', (tester) async { const childWidget = Padding(padding: EdgeInsets.zero); // Provide the childWidget to the Container. await tester.pumpWidget(Container(child: childWidget)); // Search for the childWidget in the tree and verify it exists. expect(find.byWidget(childWidget), findsOneWidget); }); ``` ## Summary ## 总结 The `find` constant provided by the `flutter_test` package provides several ways to locate widgets in the test environment. This recipe demonstrated three of these methods, and several more methods exist for different purposes. 在测试环境下，`flutter_test` package 提供的 `find` 常量 给了我们多种查找 widget 的方法。 本篇列举了三种方法，另外还有一些其他用途的方法。 If the above examples do not work for a particular use-case, see the [`CommonFinders` documentation][] to review all available methods. 如果上述示例不适用于一些特殊情况， 请到 [`CommonFinders` 文档][`CommonFinders` documentation] 中查看更多用法。 ## Complete example ## 完整样例 ```dart import 'package:flutter/material.dart'; import 'package:flutter_test/flutter_test.dart'; void main() { testWidgets('finds a Text widget', (tester) async { // Build an App with a Text widget that displays the letter 'H'. await tester.pumpWidget(const MaterialApp(home: Scaffold(body: Text('H')))); // Find a widget that displays the letter 'H'. expect(find.text('H'), findsOneWidget); }); testWidgets('finds a widget using a Key', (tester) async { // Define the test key. const testKey = Key('K'); // Build a MaterialApp with the testKey. await tester.pumpWidget(MaterialApp(key: testKey, home: Container())); // Find the MaterialApp widget using the testKey. expect(find.byKey(testKey), findsOneWidget); }); testWidgets('finds a specific instance', (tester) async { const childWidget = Padding(padding: EdgeInsets.zero); // Provide the childWidget to the Container. await tester.pumpWidget(Container(child: childWidget)); // Search for the childWidget in the tree and verify it exists. expect(find.byWidget(childWidget), findsOneWidget); }); } ``` [`Finder`]: https://api.flutter-io.cn/flutter/flutter_test/Finder-class.html [`CommonFinders` documentation]: https://api.flutter-io.cn/flutter/flutter_test/CommonFinders-class.html [`find`]: https://api.flutter-io.cn/flutter/flutter_test/find-constant.html [`flutter_test`]: https://api.flutter-io.cn/flutter/flutter_test/flutter_test-library.html [Introduction to widget testing]: /cookbook/testing/widget/introduction