delphi – TComboBox – 如何在下拉列表中调整下拉列表高度？

我受到这个问题的启发： How to make a combo box with full-text search autocomplete support？

answer工作得很好,但是当用户在列表已经下拉时键入文本时,我想调整建议列表Height / DropDownCount.

这是一个经过微小修改的MCVE – 当用户开始输入时,下拉列表将下拉,我还修复了当列表下拉时未设置为箭头的鼠标光标效果：

unit Unit1;

interface

uses
  Windows,messages,SysUtils,Variants,Classes,Graphics,Controls,Forms,Dialogs,StdCtrls,StrUtils,ExtCtrls;

type
  TComboBox = class(StdCtrls.TComboBoX)
  private
    FStoredItems: TStringList;
    FOldcursor: Tcursor; // NEW !!!
    procedure FilterItems;
    procedure StoredItemsChange(Sender: TObject);
    procedure SetStoredItems(const Value: TStringList);
    procedure CNCommand(var Amessage: TWMCommand); message CN_COMMAND; 
    procedure AdjustDropDownHeight; // NEW !!!
  protected
    // NEW !!!
    procedure KeyPress(var Key: Char); override;
    procedure DropDown; override;
    procedure CloseUp; override;
  public
    constructor Create(Aowner: TComponent); override;
    destructor Destroy; override;
    property StoredItems: TStringList read FStoredItems write SetStoredItems;
  end;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

constructor TComboBox.Create(Aowner: TComponent);
begin
  inherited;
  AutoComplete := false;
  FStoredItems := TStringList.Create;
  FStoredItems.OnChange := StoredItemsChange;
end;

destructor TComboBox.Destroy;
begin
  FStoredItems.Free;
  inherited;
end;

procedure TComboBox.CNCommand(var Amessage: TWMCommand);
begin
  // we have to process everything from our ancestor
  inherited;
  // if we received the CBN_EDITupdatE notification
  if Amessage.NotifyCode = CBN_EDITupdatE then
    // fill the items with the matches
    FilterItems;
end;

procedure TComboBox.FilterItems;
var
  I: Integer;
  SELEction: TSELEction;
begin
  // store the current combo edit SELEction
  Sendmessage(Handle,CB_GETEDITSEL,WPARAM(@SELEction.StartPos),LPARAM(@SELEction.EndPos));
  // begin with the items update
  Items.beginupdate;
  try
    // if the combo edit is not empty,then clear the items
    // and search through the FStoredItems
    if Text <> '' then
    begin
      // clear all items
      Items.Clear;
      // iterate through all of them
      for I := 0 to FStoredItems.Count - 1 do
        // check if the current one contains the text in edit
        if ContainsText(FStoredItems[I],Text) then
          // and if so,then add it to the items
          Items.Add(FStoredItems[I]);
    end
    // else the combo edit is empty
    else
      // so then we'll use all what we have in the FStoredItems
      Items.Assign(FStoredItems)
  finally
    // finish the items update
    Items.Endupdate;
  end;
  // and restore the last combo edit SELEction
  Sendmessage(Handle,CB_SETEDITSEL,MakeLParam(SELEction.StartPos,SELEction.EndPos));

  // NEW !!! - if the list is dropped down adjust the list height
  if DroppedDown then
    AdjustDropDownHeight;
end;

procedure TComboBox.StoredItemsChange(Sender: TObject);
begin
  if Assigned(FStoredItems) then
    FilterItems;
end;

procedure TComboBox.SetStoredItems(const Value: TStringList);
begin
  if Assigned(FStoredItems) then
    FStoredItems.Assign(value)
  else
    FStoredItems := Value;
end;

//  NEW !!!
procedure TComboBox.KeyPress(var Key: Char);
begin
  inherited;
  if not (Ord(Key) in [VK_RETURN,VK_ESCAPE]) then
  begin
    if (Items.Count <> 0) and not DroppedDown then
      // Sendmessage(Handle,CB_SHOWDROPDOWN,1,0); 
      DroppedDown := True;
  end;
end;

procedure TComboBox.DropDown;
begin
  FOldcursor := Screen.cursor;
  Screen.cursor := crArrow;
  inherited;
end;

procedure TComboBox.CloseUp;
begin
  Screen.cursor := FOldcursor;
  inherited;
end;

procedure TComboBox.AdjustDropDownHeight;
var
  Count: Integer;
begin
  Count := Items.Count;
  SetWindowPos(FDropHandle,Width,ItemHeight * Count +
    Height + 2,SWP_NOMOVE or SWP_NOZORDER or SWP_NOACTIVATE or SWP_NOREDRAW or
    SWP_HIDEWINDOW);
  SetWindowPos(FDropHandle,SWP_NOMOVE or SWP_NOSIZE or
    SWP_NOZORDER or SWP_NOACTIVATE or SWP_NOREDRAW or SWP_SHOWWINDOW);
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  ComboBox: TComboBox;
begin
  // here's one combo created dynamically
  ComboBox := TComboBox.Create(Self);
  ComboBox.Parent := Self;
  ComboBox.Left := 10;
  ComboBox.Top := 10;

  // here's how to fill the StoredItems
  ComboBox.StoredItems.beginupdate;
  try
    ComboBox.StoredItems.Add('Mr John Brown');
    ComboBox.StoredItems.Add('Mrs Amanda Brown');
    ComboBox.StoredItems.Add('Mr Brian Jones');
    ComboBox.StoredItems.Add('Mrs Samantha Smith');
  finally
    ComboBox.StoredItems.Endupdate;
  end;      
end;    

end.

我在FilterItems方法中添加了AdjustDropDownHeight(受TCustomcatombo.AdjustDropDown启发),但似乎没有按预期工作.窗口隐藏,并且它的高度不会根据TComboBox中的实际项目进行调整.

好像FDropHandle没有响应(或处理)SetWindowPos(FDropHandle,……在AdjustDropDownHeight方法中).

这可以修复吗？如何根据实际物品调低跌落的高度？

编辑：设置DropDownCount：= Items.Count(在答案中建议)是我尝试的第一件事(它设置最大项目数).但是,在键入文本时,下拉窗口不会更改其高度(当它已经下拉时). SetDropDownCount setter只是设置FDropDownCount：= Value.这将在下次删除下拉列表时设置下拉计数/高度.我需要它在下降时改变.希望现在更清楚.

(也许更新的Delphi版本有不同的SetDropDownCount设置器？)

为了更好地展示我想要的东西：

用户类型先生

然后太太(列表的高度调整)

然后用户按退格键给Mr(再次调整列表高度)：

编辑2：
@Dsm是正确的,并给了我正确的方向.较新的Delphi版本SetDropDownCount setter发送额外的CB_SETMINVISIBLE消息,这可以按预期工作：

procedure TCustomcatombo.SetDropDownCount(const Value: Integer);
begin
  if Value <> FDropDownCount then
  begin
    FDropDownCount := Value;
    if HandleAllocated and checkWin32Version(5,1) and themeservices.ThemesEnabled then
      Sendmessage(Handle,CB_SETMINVISIBLE,WPARAM(FDropDownCount),0);
  end;
end;

对于旧版本定义：

const
  CBM_FIRST               = $1700;
  CB_SETMINVISIBLE        = CBM_FIRST + 1;

procedure TComboBox.AdjustDropDownHeight;
begin
  DropDownCount := Items.Count;
end;