捕获/创建TCustomControl Delphi的OnGetFocus / OnLostFocus事件

Question

我创建了一个继承自TCustomControl的Delphi组件。该组件可以从TWinControl继承而成为焦点，但是当它聚焦时我需要“突出显示”并在失去焦点时更改某些属性。 正如Delphi文档所说，TCustomControl没有继承的OnFocus事件，所以我需要捕获事件（？）并实现我自己的OnGetFocus / OnLostFocus事件处理程序（？）。 当组件获得/失去焦点时，如何捕获事件？

Answer 1

控件接收或丢失输入焦点时触发的事件是OnEnter和OnExit，并且是作为组件开发人员的DoEnter和DoExit方法触发的应该覆盖：

type
  TMyControl = class(TCustomControl)
  protected
    procedure DoEnter; override;
    procedure DoExit; override;
  end;

implementation

{ TMyControl }

procedure TMyControl.DoEnter;
begin
  inherited;
  // the control received the input focus, so do what you need here; note
  // that it's recommended to call inherited inside this method (which as
  // described in the reference should only fire the OnEnter event now)
end;

procedure TMyControl.DoExit;
begin
  inherited;
  // the control has lost the input focus, so do what you need here; note
  // that it's recommended to call inherited inside this method (which as
  // described in the reference should only fire the OnExit event now)
end;