Delphi XE 和带 OnKeyDown 的捕获箭头键 [英] Delphi XE and Trapping Arrow Key with OnKeyDown

问题描述

我想让我的表单处理箭头键，我可以做到——只要表单上没有按钮.这是为什么?

I want my form to handle the arrow keys, and I can do it -- as long as there is no button on the form. Why is this?

推荐答案

关键消息由接收这些消息的控件本身处理，这就是为什么当您在按钮上时表单没有接收到消息的原因.所以通常你必须对这些控件进行子类化，但 VCL 很友好地询问父母表单如果表单有兴趣该怎么做:

Key messages are processed by the controls themselves who receives these messages, that's why when you're on a button the form is not receiving the message. So normally you would have to subclass these controls, but the VCL is kind enough to ask the parenting form what to do if the form is interested:

type
  TForm1 = class(TForm)
    ..
  private
    procedure DialogKey(var Msg: TWMKey); message CM_DIALOGKEY;
    ..


procedure TForm1.DialogKey(var Msg: TWMKey); 
begin
  if not (Msg.CharCode in [VK_DOWN, VK_UP, VK_RIGHT, VK_LEFT]) then
    inherited;
end;

François 要回答 OP 原始问题，您需要以某种方式调用 onKeyDown 以便他的事件代码可以工作(随意编辑；评论太长).

François editing: to answer the OP original question, you need to call onKeyDown somehow so that his event code would work (feel free to edit; was too long for a comment).

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    procedure FormKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
  private
    { Private declarations }
    procedure DialogKey(var Msg: TWMKey); message CM_DIALOGKEY;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.DialogKey(var Msg: TWMKey);
begin
  case Msg.CharCode of
    VK_DOWN, VK_UP, VK_RIGHT, VK_LEFT:
      if Assigned(onKeyDown) then
        onKeyDown(Self, Msg.CharCode, KeyDataToShiftState(Msg.KeyData));
    else
      inherited
  end;
end;

procedure TForm1.FormKeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  case Key of
    VK_DOWN: Top := Top + 5;
    VK_UP: Top := Top - 5;
    VK_LEFT: Left := Left - 5;
    VK_RIGHT: Left := Left + 5;
  end;
end;

这篇关于Delphi XE 和带 OnKeyDown 的捕获箭头键的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！