flutter在ios模拟器运行不起来

Question

刚创建项目，是没问题的。
中间stop了一次，然后在Start Debugging就这样了

Launching lib/main.dart on iPhone X in debug mode...
Xcode build done.                                            7.5s
Failed to build iOS app
Error output from Xcode build:
↳
    ** BUILD FAILED **
Xcode's output:
↳
    === BUILD TARGET Runner OF PROJECT Runner WITH CONFIGURATION Debug ===
    The use of Swift 3 @objc inference in Swift 4 mode is deprecated. Please address deprecated @objc inference warnings, test your code with “Use of deprecated Swift 3 @objc inference” logging enabled, and then disable inference by changing the "Swift 3 @objc Inference" build setting to "Default" for the "Runner" target.
    /* com.apple.actool.errors */
    /Users/watasi/workspace/flutter/chat/ios/Runner/Assets.xcassets: error: Failed to find a suitable device for the type IBSimDeviceTypeiPad2x (com.apple.dt.Xcode.IBSimDeviceType.iPad-2x) with runtime iOS 12.4 (12.4 - 16G73) - com.apple.CoreSimulator.SimRuntime.iOS-12-4
        Failure Reason: Failed to create new simulator device that matches IBSimDeviceTypeiPad2x (com.apple.dt.Xcode.IBSimDeviceType.iPad-2x) for runtime iOS 12.4 (12.4 - 16G73) - com.apple.CoreSimulator.SimRuntime.iOS-12-4 (Invalid runtime: com.apple.CoreSimulator.SimRuntime.iOS-12-4)
        Underlying Errors:
            Description: Invalid runtime: com.apple.CoreSimulator.SimRuntime.iOS-12-4
    /* com.apple.actool.compilation-results */
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/[e-mail]
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/[e-mail]
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/AppIcon29x29.png
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/[e-mail]
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/[e-mail]
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/[e-mail]
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/[e-mail]
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/[e-mail]
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/[e-mail]
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/AppIcon20x20~ipad.png
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/AppIcon20x20@2x~ipad.png
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/AppIcon29x29~ipad.png
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/AppIcon29x29@2x~ipad.png
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/AppIcon40x40~ipad.png
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/AppIcon40x40@2x~ipad.png
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/AppIcon76x76~ipad.png
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/AppIcon76x76@2x~ipad.png
    /Users/watasi/workspace/flutter/chat/build/ios/Debug-iphonesimulator/Runner.app/AppIcon83.5x83.5@2x~ipad.png
    /Users/watasi/Library/Developer/Xcode/DerivedData/Runner-faogbthcxowvrqfidwzcmaxoxmrk/Build/Intermediates.noindex/
Runner.build/Debug-iphonesimulator/Runner.build/assetcatalog_generated_info.plist
Could not build the application for the simulator.
Error launching application on iPhone X.
Exited (sigterm)