Issue 1:
PlatformException (PlatformException(error, Calling startActivity() from outside of an Activity context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want?, null))

after downgrading to 3.0.0 it Works well

Issue 2:
I cloned the Flutter repo today to check why following error occur when using url_launcher. I have tried latest package and also placing any. Most importantly when it is not working I just copy pasted the doc example: https://flutter.io/docs/development/packages-and-plugins/using-packages but still I get the same error message, no luck.

Log

E/MethodChannel#plugins.flutter.io/url_launcher(31054): Failed to handle method call
E/MethodChannel#plugins.flutter.io/url_launcher(31054): android.util.AndroidRuntimeException: Calling startActivity() from outside of an Activity context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want?
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at android.app.ContextImpl.startActivity(ContextImpl.java:1140)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at android.app.ContextImpl.startActivity(ContextImpl.java:1127)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at android.content.ContextWrapper.startActivity(ContextWrapper.java:311)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at io.flutter.plugins.urllauncher.UrlLauncherPlugin.onMethodCall(UrlLauncherPlugin.java:61)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:200)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at io.flutter.view.FlutterNativeView.handlePlatformMessage(FlutterNativeView.java:163)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at android.os.MessageQueue.nativePollOnce(Native Method)E/MethodChannel#plugins.flutter.io/url_launcher(31054): at android.os.MessageQueue.next(MessageQueue.java:138)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at android.os.Looper.loop(Looper.java:150)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at android.app.ActivityThread.main(ActivityThread.java:5398)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at java.lang.reflect.Method.invokeNative(Native Method)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at java.lang.reflect.Method.invoke(Method.java:515)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:940)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
E/MethodChannel#plugins.flutter.io/url_launcher(31054): at dalvik.system.NativeStart.main(Native Method)
E/flutter (31054): [ERROR:flutter/shell/common/shell.cc(184)] Dart Error: Unhandled exception:
E/flutter (31054): PlatformException(error, Calling startActivity() from outside of an Activity context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want?, null)
E/flutter (31054): #0 StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:551:7)
E/flutter (31054): #1 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:292:18)
E/flutter (31054): <asynchronous suspension>
E/flutter (31054): #2 launch (package:url_launcher/url_launcher.dart:66:19)
E/flutter (31054): #3 DemoPage.launchURL (package:nov29long/main.dart:19:5)
E/flutter (31054): #4 _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:507:14)
E/flutter (31054): #5 _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:562:30)
E/flutter (31054): #6 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:102:24)
E/flutter (31054): #7 TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:242:9)
E/flutter (31054): #8 TapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:175:7)
E/flutter (31054): #9 PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:315:9)
E/flutter (31054): #10 PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:73:12)
E/flutter (31054): #11 PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101:11)
E/flutter (31054): #12 _WidgetsFlutterBinding&BindingBase&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:180:19)
E/flutter (31054): #13 _WidgetsFlutterBinding&BindingBase&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:158:22)
E/flutter (31054): #14 _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:138:7)
E/flutter (31054): #15 _WidgetsFlutterBinding&BindingBase&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:101:7)
E/flutter (31054): #16 _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:85:7)
E/flutter (31054): #17 _invoke1 (dart:ui/hooks.dart:168:13)
E/flutter (31054): #18 _dispatchPointerDataPacket (dart:ui/hooks.dart:122:5)

Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel beta, v0.11.12, on Microsoft Windows [Version 10.0.14393], locale en-US)
[!] Android toolchain - develop for Android devices (Android SDK 28.0.3)
X Android license status unknown.
[√] Android Studio (version 3.1)
[√] IntelliJ IDEA Community Edition (version 2017.3)
[√] IntelliJ IDEA Community Edition (version 2018.1)
[√] VS Code, 32-bit edition
[√] VS Code, 64-bit edition (version 1.29.1)
[√] Connected device (1 available)

! Doctor found issues in 1 category.