小编TUS*_*HAR的帖子

每当我尝试运行 flutter 应用程序时，都会收到此错误。

../flutter/.pub-cache/hosted/pub.dartlang.org/percent_indicator-4.2.1/lib/linear_percent_indicator.dart:162:5: Warning: The class 'WidgetsBinding' cannot be null.\nTry replacing '?.' with '.'\n    WidgetsBinding?.instance.addPostFrameCallback((_) {\n    ^^^^^^^^^^^^^^\n../flutter/.pub-cache/hosted/pub.dartlang.org/percent_indicator-4.2.1/lib/linear_percent_indicator.dart:162:30: Error: Method 'addPostFrameCallback' cannot be called on 'WidgetsBinding?' because it is potentially null.\n - 'WidgetsBinding' is from 'package:flutter/src/widgets/binding.dart' ('../flutter/packages/flutter/lib/src/widgets/binding.dart').\nTry calling using ?. instead.\n    WidgetsBinding?.instance.addPostFrameCallback((_) {\n                             ^^^^^^^^^^^^^^^^^^^^\n\n\nFAILURE: Build failed with an exception.\n\n* Where:\nScript '/home/user/Downloads/flutter/packages/flutter_tools/gradle/flutter.gradle' line: 1102\n\n* What went wrong:\nExecution failed for task ':app:compileFlutterBuildDebug'.\n> Process 'command '/home/user/Downloads/flutter/bin/flutter'' finished with non-zero exit value 1\n\n* Try:\nRun with --stacktrace option to get the stack trace. Run …

我正在尝试创建一个计时器应用程序，它具有针对不同任务的多个倒数计时器。问题，我面临的是，如果我启动一个计时器，然后按后退按钮，计时器就会停止。所以我希望，该计时器一直运行，直到它被暂停或计时器结束并提醒用户或应用程序被销毁。请帮助我如何使用 Flutter 做到这一点？我也使用 sql-lite 来存储所有计时器。

我正在使用file_picker 5.0.1，当从 Android 设备图库应用程序中选择图像时，它显示此错误。

I/FilePickerDelegate(26740): User cancelled the picker request

这是代码片段，我用来调用文件选择器

 FilePickerResult? result =
                            await  FilePicker.platform
                                .pickFiles(
                              type: FileType.image,
                                    allowMultiple: false,
                                    allowCompression: false,
                                    });
                            
                            if (result != null) {
                              print(result.files.length);


                            }

我的颤振版本：3.0.5 AndroidcompileSdkVersion：31 Android minSdkVersion：19 Android targetSdkVersion：31