這次用DBLookupCombobox實現省份-城市-地區的下拉聯動，用以學習DBLookupCombobox的一些用法

效果圖：

首先建立數據表（數據表形式可以多種多樣：數據庫表、文本、xml等，最終能轉換成Dataset數據集就好，這裏使用數據庫表）

1.省份表

2.城市表

3.地區表

時間關系，就簡單做了幾個數據，只有廣東-廣州-地區是完整的數據

建表及數據代碼：

USE [his_mz]
GO
/****** Object:  Table [dbo].[City]    Script Date: 2018-8-19 23:04:00 ******/
SET ANSI_NULLS ON
 

GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[City](
    [code] [varchar](10) NOT NULL,
    [name] [varchar](50) NOT NULL,
    [province] [varchar](10) NOT NULL,
    [other] [varchar](50) NULL,
 CONSTRAINT [PK_City] PRIMARY KEY CLUSTERED 
(
    [code] ASC
)WITH (PAD_INDEX = OFF
 
, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO
SET ANSI_PADDING OFF
GO
/****** Object:  Table [dbo].[district]    Script Date: 2018-8-19 23:04:00 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
 

GO
CREATE TABLE [dbo].[district](
    [code] [varchar](10) NOT NULL,
    [name] [varchar](50) NOT NULL,
    [city] [varchar](10) NOT NULL,
    [other] [varchar](50) NULL
) ON [PRIMARY]

GO
SET ANSI_PADDING OFF
GO
/****** Object:  Table [dbo].[province]    Script Date: 2018-8-19 23:04:00 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[province](
    [code] [varchar](10) NOT NULL,
    [name] [varchar](50) NOT NULL,
    [other] [varchar](50) NULL
) ON [PRIMARY]

GO
SET ANSI_PADDING OFF
GO
INSERT [dbo].[City] ([code], [name], [province], [other]) VALUES (N‘c1001‘, N‘北京市‘, N‘1001‘, NULL)
GO
INSERT [dbo].[City] ([code], [name], [province], [other]) VALUES (N‘c1002‘, N‘上海市‘, N‘1001‘, NULL)
GO
INSERT [dbo].[City] ([code], [name], [province], [other]) VALUES (N‘c1003‘, N‘天津市‘, N‘1001‘, NULL)
GO
INSERT [dbo].[City] ([code], [name], [province], [other]) VALUES (N‘c1004‘, N‘重慶市‘, N‘1001‘, NULL)
GO
INSERT [dbo].[City] ([code], [name], [province], [other]) VALUES (N‘c1005‘, N‘廣州市‘, N‘1002‘, NULL)
GO
INSERT [dbo].[City] ([code], [name], [province], [other]) VALUES (N‘c1006‘, N‘深圳市‘, N‘1002‘, NULL)
GO
INSERT [dbo].[City] ([code], [name], [province], [other]) VALUES (N‘c1007‘, N‘珠海市‘, N‘1002‘, NULL)
GO
INSERT [dbo].[City] ([code], [name], [province], [other]) VALUES (N‘c1008‘, N‘南寧市‘, N‘1003‘, NULL)
GO
INSERT [dbo].[City] ([code], [name], [province], [other]) VALUES (N‘c1009‘, N‘玉林市‘, N‘1003‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1001‘, N‘越秀區‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1002‘, N‘荔灣區‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1003‘, N‘天河區‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1004‘, N‘海珠區‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1005‘, N‘黃浦區‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1006‘, N‘蘿崗區‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1007‘, N‘芳村區‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1008‘, N‘白雲區‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1009‘, N‘花都區‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1010‘, N‘增城區‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1011‘, N‘從化區‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[province] ([code], [name], [other]) VALUES (N‘1001‘, N‘直轄市‘, NULL)
GO
INSERT [dbo].[province] ([code], [name], [other]) VALUES (N‘1002‘, N‘廣東省‘, NULL)
GO
INSERT [dbo].[province] ([code], [name], [other]) VALUES (N‘1003‘, N‘廣西壯族自治區‘, NULL)
GO

窗體大概放這些控件，都是Delphi自帶的。（如果安裝了Ehlib包，用DBLookupComboboxEh效果更佳）

DBLookupCombobox的屬性設置及說明

ListSource：下拉列表的數據集

ListField：下拉列表要顯示的字段的名稱

KeyField：要獲得的字段值。例如廣東對應的記錄，1002，廣東省。如果廣東省被選擇了，那麽DBLookupCombobox.KeyValue的值就取字段name為廣東的那條記錄的code值（1002）

初始化數據集

procedure TForm2.FormCreate(Sender: TObject);
begin
  //初始化數據集信息
  qryProvince.Close;
  qryCity.Close;
  qryDistrict.Close;

  qryProvince.SQL.Text := ‘select * from province‘;
  qryCity.SQL.Text := ‘select * from city‘;
  qryDistrict.SQL.Text := ‘select * from district‘;

  qryProvince.Open;
  qryCity.Open;
  qryDistrict.Open;

  //打開數據集
  qryProvince.Open;
  qryCity.Open;
  qryDistrict.Open;

  //初始化DBLookupcombobox
  qryCity.Filtered := False;
  qryCity.Filter := ‘code=‘+QuotedStr(‘‘);
  qryCity.Filtered := True;

  qryDistrict.Filtered := False;
  qryDistrict.Filter := ‘code=‘+QuotedStr(‘‘);
  qryDistrict.Filtered := True;
end;

當省份選擇之後，觸發DBLookupCombobox的CloseUp事件

procedure TForm2.cbProvinceCloseUp(Sender: TObject);
var
  keycode: string;
begin
  if cbProvince.Text=EmptyStr then
    keycode := EmptyStr
  else
    keycode := cbProvince.KeyValue; //關鍵是keyvalue,keyvalue的值來自於keyField，可以在屬性面板設置keyFiled

  //使用filter過濾，只顯示Province=keycode的數據集
  qryCity.Filtered := False;
  qryCity.Filter := ‘Province=‘+QuotedStr(keycode);
  qryCity.Filtered := True;

  //清除城市下拉框已選的值
  cbCity.KeyValue := ‘‘;
  cbDistrict.KeyValue := ‘‘;
end;

當城市選擇之後

procedure TForm2.cbCityCloseUp(Sender: TObject);
var
  keycode: string;
begin
  if cbCity.Text=EmptyStr then                
    keycode := EmptyStr
  else
    keycode := cbCity.KeyValue;
  //使用filter過濾，只顯示city=keycode的數據集
  qryDistrict.Filtered := False;
  qryDistrict.Filter := ‘city=‘+QuotedStr(keycode);
  qryDistrict.Filtered := True;
  //由於有些城市的區域為空，所以要把DBLookupCombobox的enable設置FALSE，否則會報錯
  if qryDistrict.RecordCount=0 then
    cbDistrict.Enabled := False
  else
    cbDistrict.Enabled := True;

  //清除已選擇的地區的值
  cbDistrict.KeyValue := ‘‘;
end;

DBLookupCombobox實現下拉聯動