Flutter Framework’unun yeni sürümüyle birlikte baze Package’larda hatalar meydana gelebiliyor. Flutter 1.20.3 sürümü 02.09.2020 tarihinde yayımlandı. flutter_cupertino_date_picker; package kullanımında run/debug esnasında build edilirken aşağıdaki hatayla karşılaşıcaksınız ve çözümünü fotoğraflar ile destekledim.

Error: The type ‘DiagnosticableMixin’can’t be mixed in.

/C:/src/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_cupertino_date_picker-1.0.26+2/lib/src/date_picker_theme.dart:23:32: Error: Type ‘DiagnosticableMixin’ not found.
class DateTimePickerTheme with DiagnosticableMixin {
^^^^^^^^^^^^^^^^^^^
/C:/src/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_cupertino_date_picker-1.0.26+2/lib/src/date_picker_theme.dart:23:7: Error: The type ‘DiagnosticableMixin’ can’t be mixed in.
class DateTimePickerTheme with DiagnosticableMixin {
^

FAILURE: Build failed with an exception.

  • Where:
    Script ‘C:\src\flutter\packages\flutter_tools\gradle\flutter.gradle’ line: 896
  • What went wrong:
    Execution failed for task ‘:app:compileFlutterBuildDebug’.

Process ‘command ‘C:\src\flutter\bin\flutter.bat” finished with non-zero exit value 1

  • Try:
    Run with –stacktrace option to get the stack trace. Run with –info or –debug option to get more log output. Run with –scan to get full insights.
  • Get more help at https://help.gradle.org

BUILD FAILED in 17s
Exception: Gradle task assembleDebug failed with exit code 1

Step1:

Error: The type ‘DiagnosticableMixin’can’t be mixed in.

Step2:

DiagnosticableMixin change Diagnosticable 

Solution:

DiagnosticableMixin change Diagnosticable 
Terminal: flutter clean

package: flutter_cupertino_date_picker