Delphi XE和陷阱箭头键与OnKeyDown [英] Delphi XE and Trapping Arrow Key with OnKeyDown

问题描述

我想要我的窗体处理箭头键，我可以做 - 只要窗体上没有按钮。为什么是这样？

解决方案

主要消息由接收这些消息的控件本身处理，这就是为什么当你在按钮表单没有收到消息。所以通常你必须对这些控件进行子类化，但是如果表单感兴趣，则VCL很适合请教父母表单：

  type 
 TForm1 = class（TForm）
 .. 
 private 
 procedure DialogKey（var Msg：TWMKey）;消息CM_DIALOGKEY; 
 .. 
 
 
程序TForm1.DialogKey（var Msg：TWMKey）; 
 begin 
如果没有（Msg.CharCode在[VK_DOWN，VK_UP，VK_RIGHT，VK_LEFT]）然后
继承; 
结束
  

François编辑：回答OP原始问题，您需要打电话onKeyDown不知何故，以便他的事件代码可以工作（随时可以编辑;对于评论太长了）。

 键入
 TForm1 = class（TForm）
 Button1：TButton; 
 Button2：TButton; 
 Button3：TButton; 
 Button4：TButton; 
 procedure FormKeyDown（Sender：TObject; var Key：Word; Shift：TShiftState）; 
 private 
 {私有声明} 
程序DialogKey（var Msg：TWMKey）;消息CM_DIALOGKEY; 
 public 
 {公开声明} 
 end; 
 
 var 
 Form1：TForm1; 
 
执行
 
 {$ R * .dfm} 
 
程序TForm1.DialogKey（var Msg：TWMKey）; 
 begin 
 case Msg.CharCode 
 VK_DOWN，VK_UP，VK_RIGHT，VK_LEFT：
如果已分配（onKeyDown）然后
 onKeyDown（Self，Msg.CharCode，KeyDataToShiftState（ Msg.KeyData））; 
 else 
继承
 end; 
结束
 
程序TForm1.FormKeyDown（发件人：TObject; var Key：Word; 
 Shift：TShiftState）; 
 begin 
 case 
的关键字VK_DOWN：Top：= Top + 5; 
 VK_UP：Top：= Top  -  5; 
 VK_LEFT：左：=左 -  5; 
 VK_RIGHT：Left：= Left + 5; 
结束
结束
  

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?

解决方案

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 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;

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