Delphi：测试事件处理程序分配 [英] Delphi: Test event handler assignment

问题描述

我想在构造函数中分配一个事件处理程序，如果它没有一个分配。因此，我想删除析构函数中最终分配的事件处理程序。我写的代码如下，但不能编译。

I want to assign an event handler in constructor, if it does not have one assigned. Consequentially I want to remove the eventually assigned event handler in destructor. I wrote the code as follows, but cannot be compiled.

constructor TSomeControl.Create(Panel: TPanel);
begin
  inherited Create;
  FPanel := Panel;
  if not Assigned(FPanel.OnResize) then
    FPanel.OnResize := HandlePanelResize;
end;

destructor TSomeControl.Destroy;
begin
  if @FPanel.OnResize = @HandlePanelResize then // [dcc32 Error] E2036 Variable required
    FPanel.OnResize := nil;
  FPanel := nil;
  inherited;
end;

如何正确测试？我知道一个解决方案是使用变量进行记录，无论我是否已经分配了 OnResize 。但是我不希望这是解决方案。

How to test it properly? I know a solution is to use a variable to record, whether I have assigned OnResize. But I do not want this as solution.

推荐答案

不需要在这里编写任何自定义代码，因为您可以使用已经存在的compare从 Generics.Defaults ：

No need to write any custom code here as you can use the already existing comparers from Generics.Defaults:

destructor TSomeControl.Destroy;
begin
  if Assigned(FPanel) and TEqualityComparer<TNotifyEvent>.Default.Equals(
    FPanel.OnResize, HandlePanelResize) then
    FPanel.OnResize := nil;
  FPanel := nil;
  inherited;
end;

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