GestureRecognizer 清理

OneSequenceGestureRecognizer.addAllowedPointer() 已更改為接受 PointerDownEvent，就像其超類一樣。之前，它接受更通用的 PointerEvent 型別，這是不正確的。

框架僅將 PointerDownEvent 物件傳遞給 addAllowedPointer()。將 OneSequenceGestureRecognizer.addAllowedPointer() 宣告為接受更通用的型別會造成混淆，並導致 OneSequenceGestureRecognizer 的子類必須將其引數轉換為正確的類。

先前的宣告強制 OneSequenceGestureRecognizer 的後代像這樣覆蓋 addAllowedPointer()

dartclass CustomGestureRecognizer extends ScaleGestureRecognizer {
  @override
  void addAllowedPointer(PointerEvent event) {
    // insert custom handling of event here...
    super.addAllowedPointer(event);
  }
}

新的方法宣告將導致此程式碼因以下錯誤訊息而失敗

super.addAllowedPointer(event); The argument type 'PointerEvent' can't be assigned to the parameter type 'PointerDownEvent'.
                                #argument_type_not_assignable

遷移前的程式碼

dartclass CustomGestureRecognizer extends ScaleGestureRecognizer {
  @override
  void addAllowedPointer(PointerEvent event) {
    // insert custom handling of event here...
    super.addAllowedPointer(event);
  }
}

遷移後的程式碼

dartclass CustomGestureRecognizer extends ScaleGestureRecognizer {
  @override
  void addAllowedPointer(PointerDownEvent event) {
    // insert custom handling of event here...
    super.addAllowedPointer(event);
  }
}