监听时在颤振中使用 Provider 的问题：true

Question

我正在 Flutter 中开发一个应用程序。我尝试在应用程序中使用 Provider 但遇到了这个错误：

Tried to listen to a value exposed with provider, from outside of the widget tree.
E/flutter ( 2850): 
E/flutter ( 2850): This is likely caused by an event handler (like a button's onPressed) that called
E/flutter ( 2850): Provider.of without passing `listen: false`.
E/flutter ( 2850): 
E/flutter ( 2850): To fix, write:
E/flutter ( 2850): Provider.of<Complexes>(context, listen: false);
E/flutter ( 2850): 
E/flutter ( 2850): It is unsupported because may pointlessly rebuild the widget associated to the
E/flutter ( 2850): event handler, when the widget tree doesn't care about the value.

我的代码是：

Tried to listen to a value exposed with provider, from outside of the widget tree.
E/flutter ( 2850): 
E/flutter ( 2850): This is likely caused by an event handler (like a button's onPressed) that called
E/flutter ( 2850): Provider.of without passing `listen: false`.
E/flutter ( 2850): 
E/flutter ( 2850): To fix, write:
E/flutter ( 2850): Provider.of<Complexes>(context, listen: false);
E/flutter ( 2850): 
E/flutter ( 2850): It is unsupported because may pointlessly rebuild the widget associated to the
E/flutter ( 2850): event handler, when the widget tree doesn't care about the value.

设置为 时listen:false，问题解决。但我认为这不是解决这个问题的好方法。另外，我需要提供者倾听。我已经搜索了互联网，但找不到任何合适的解决方案。

这是我的 Flutter 医生：

[?] Flutter (Channel stable, v1.12.13+hotfix.7, on Microsoft Windows [Version 10.0.18363.657],    locale en-US)
   • Flutter version 1.12.13+hotfix.7 at C:\android\flutter
   • Framework revision 9f5ff2306b (6 weeks ago), 2020-01-26 22:38:26 -0800
   • Engine revision a67792536c
   • Dart version 2.7.0

[?] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
    • Android SDK at C:/android/sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-29, build-tools 28.0.3
    • ANDROID_HOME = C:/android/sdk
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)
    • All Android licenses accepted.

[?] Android Studio (version 3.6)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin version 43.0.2
    • Dart plugin version 192.7761
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)

[?] IntelliJ IDEA Ultimate Edition (version 2019.3)
    • IntelliJ at C:\Program Files\JetBrains\IntelliJ IDEA 2019.2.4
    • Flutter plugin version 42.1.4
    • Dart plugin version 193.5731

[!] VS Code (version 1.41.1)
    • VS Code at C:\Users\Altay\AppData\Local\Programs\Microsoft VS Code
    X Flutter extension not installed; install from
      https://marketplace.visualstudio.com/items?itemName=Dart-Code.flutter

[?] Connected device (1 available)
    • Android SDK built for x86 • emulator-5554 • android-x86 • Android 5.0.2 (API 21) (emulator)

! Doctor found issues in 1 category.
Process finished with exit code 0

我的提供者块：

loadedComplexes = Provider.of<Complexes>(context, listen: true).favoriteItems;

调用提供者的方法：

[?] Flutter (Channel stable, v1.12.13+hotfix.7, on Microsoft Windows [Version 10.0.18363.657],    locale en-US)
   • Flutter version 1.12.13+hotfix.7 at C:\android\flutter
   • Framework revision 9f5ff2306b (6 weeks ago), 2020-01-26 22:38:26 -0800
   • Engine revision a67792536c
   • Dart version 2.7.0

[?] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
    • Android SDK at C:/android/sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-29, build-tools 28.0.3
    • ANDROID_HOME = C:/android/sdk
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)
    • All Android licenses accepted.

[?] Android Studio (version 3.6)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin version 43.0.2
    • Dart plugin version 192.7761
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)

[?] IntelliJ IDEA Ultimate Edition (version 2019.3)
    • IntelliJ at C:\Program Files\JetBrains\IntelliJ IDEA 2019.2.4
    • Flutter plugin version 42.1.4
    • Dart plugin version 193.5731

[!] VS Code (version 1.41.1)
    • VS Code at C:\Users\Altay\AppData\Local\Programs\Microsoft VS Code
    X Flutter extension not installed; install from
      https://marketplace.visualstudio.com/items?itemName=Dart-Code.flutter

[?] Connected device (1 available)
    • Android SDK built for x86 • emulator-5554 • android-x86 • Android 5.0.2 (API 21) (emulator)

! Doctor found issues in 1 category.
Process finished with exit code 0

如果有必要，我可以提供更多信息。这个问题有什么解决方案吗？

提前致谢。

Answer 1

该错误清楚地表明您将其声明在Widget树的外面。如果要设置listen为 true，则必须在Widget树中声明它，以便提供程序知道Widget发生更改时必须重建哪棵树。

例子

class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
 loadedComplexes = Provider.of<Complexes>(context, listen: true).favoriteItems;//You must declare here if listen to true
  return Scaffold(
    body: Center(
      child: MyWidget(),
    ),
 );

} }

设置listen为true使整个小部件作为侦听器并导致重建整个小部件树。但是设置 listen tofalse将帮助您重建您声明为的特定小部件Consumer（消费者是一个监听更改的小部件）。

检查这个视频伙伴。他用的方法和你一样

Answer 2

将 Listen 设置为 false 并不是一个坏习惯。它在访问提供程序值一次或调用提供程序方法时使用。

如果您想收听更新，您可以在许多不同的提供商之间进行选择。