适配Android11 READ_EXTERNAL_STORAGE，没有外部权限报错

[azhansy]

[✓] Flutter (Channel stable, 2.10.5, on macOS 12.0.1 21A559 darwin-x64, locale zh-Hans-KH) • Flutter version 2.10.5 at /Users/shu/company/flutter/flutter • Upstream repository https://github.com/flutter/flutter.git • Framework revision 5464c5bac7 (7 days ago), 2022-04-18 09:55:37 -0700 • Engine revision 57d3bac3dd • Dart version 2.16.2 • DevTools version 2.9.2

[✓] Android toolchain - develop for Android devices (Android SDK version 32.1.0-rc1) • Android SDK at /Users/shu/company/sdk • Platform android-32, build-tools 32.1.0-rc1 • ANDROID_HOME = /Users/shu/company/sdk • Java binary at: /Applications/Android Studio.app/Contents/jre/Contents/Home/bin/java • Java version OpenJDK Runtime Environment (build 11.0.11+0-b60-7590822) • All Android licenses accepted.

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[✓] Android Studio (version 2021.1) • Android Studio at /Applications/Android Studio.app/Contents • Flutter plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/9212-flutter • Dart plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/6351-dart • Java version OpenJDK Runtime Environment (build 11.0.11+0-b60-7590822)

[✓] VS Code (version 1.64.0) • VS Code at /Applications/Visual Studio Code.app/Contents • Flutter extension version 3.34.0

[✓] Connected device (3 available) • IN2020 (mobile) • b1c1c100 • android-arm64 • Android 12 (API 31) • macOS (desktop) • macos • darwin-x64 • macOS 12.0.1 21A559 darwin-x64 • Chrome (web) • chrome • web-javascript • Google Chrome 100.0.4896.127

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E/flutter (32220): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: PlatformException(error, Attempt to invoke virtual method 'int android.content.Context.checkPermission(java.lang.String, int, int)' on a null object reference, null, java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.Context.checkPermission(java.lang.String, int, int)' on a null object reference E/flutter (32220): at androidx.core.content.ContextCompat.checkSelfPermission(ContextCompat.java:555) E/flutter (32220): at com.mengtnt.export_video_frame.PermissionManager.isPermissionGranted(PermissionManager.java:53) E/flutter (32220): at com.mengtnt.export_video_frame.ExportVideoFramePlugin.onMethodCall(ExportVideoFramePlugin.java:65) E/flutter (32220): at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:262) E/flutter (32220): at io.flutter.embedding.engine.dart.DartMessenger.invokeHandler(DartMessenger.java:296) E/flutter (32220): at io.flutter.embedding.engine.dart.DartMessenger.lambda$dispatchMessageToQueue$0$DartMessenger(DartMessenger.java:320) E/flutter (32220): at io.flutter.embedding.engine.dart.-$$Lambda$DartMessenger$TsixYUB5E6FpKhMtCSQVHKE89gQ.run(Unknown Source:12) E/flutter (32220): at android.os.Handler.handleCallback(Handler.java:938) E/flutter (32220): at android.os.Handler.dispatchMessage(Handler.java:99) E/flutter (32220): at android.os.Looper.loopOnce(Looper.java:201) E/flutter (32220): at android.os.Looper.loop(Looper.java:288) E/flutter (32220): at android.app.ActivityThread.main(ActivityThread.java:7839) E/flutter (32220): at java.lang.reflect.Method.invoke(Native Method) E/flutter (32220): at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:550) E/flutter (32220): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003) E/flutter (32220): ) E/flutter (32220): #0 StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:607:7) E/flutter (32220): #1 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:177:18) E/flutter (32220): E/flutter (32220): #2 ExportVideoFrame.exportImageBySeconds (package:export_video_frame/export_video_frame.dart:131:9) E/flutter (32220):