DBLookupCombobox实现下拉联动

这次用DBLookupCombobox实现省份-城市-地区的下拉联动，用以学习DBLookupCombobox的一些用法

效果图：

首先建立数据表（数据表形式可以多种多样：数据库表、文本、xml等，最终能转换成Dataset数据集就好，这里使用数据库表）

1.省份表

2.城市表

3.地区表

时间关系，就简单做了几个数据，只有广东-广州-地区是完整的数据

建表及数据代码：

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‘重庆市‘, N‘1001‘, NULL)
GO
INSERT [dbo].[City] ([code], [name], [province], [other]) VALUES (N‘c1005‘, N‘广州市‘, 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‘南宁市‘, 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‘越秀区‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1002‘, N‘荔湾区‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1003‘, N‘天河区‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1004‘, N‘海珠区‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1005‘, N‘黄浦区‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1006‘, N‘萝岗区‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1007‘, N‘芳村区‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1008‘, N‘白云区‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1009‘, N‘花都区‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1010‘, N‘增城区‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[district] ([code], [name], [city], [other]) VALUES (N‘d1011‘, N‘从化区‘, N‘c1005‘, NULL)
GO
INSERT [dbo].[province] ([code], [name], [other]) VALUES (N‘1001‘, N‘直辖市‘, NULL)
GO
INSERT [dbo].[province] ([code], [name], [other]) VALUES (N‘1002‘, N‘广东省‘, NULL)
GO
INSERT [dbo].[province] ([code], [name], [other]) VALUES (N‘1003‘, N‘广西壮族自治区‘, NULL)
GO

建表及数据SQL

窗体大概放这些控件，都是Delphi自带的。（如果安装了Ehlib包，用DBLookupComboboxEh效果更佳）

DBLookupCombobox的属性设置及说明

ListSource：下拉列表的数据集

ListField：下拉列表要显示的字段的名称

KeyField：要获得的字段值。例如广东对应的记录，1002，广东省。如果广东省被选择了，那么DBLookupCombobox.KeyValue的值就取字段name为广东的那条记录的code值（1002）

初始化数据集

procedure TForm2.FormCreate(Sender: TObject);
begin
  //初始化数据集信息
  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;

  //打开数据集
  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;

初始化数据集

当省份选择之后，触发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; //关键是keyvalue,keyvalue的值来自于keyField，可以在属性面板设置keyFiled

  //使用filter过滤，只显示Province=keycode的数据集
  qryCity.Filtered := False;
  qryCity.Filter := ‘Province=‘+QuotedStr(keycode);
  qryCity.Filtered := True;

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

当省份选择之后

当城市选择之后

procedure TForm2.cbCityCloseUp(Sender: TObject);
var
  keycode: string;
begin
  if cbCity.Text=EmptyStr then
    keycode := EmptyStr
  else
    keycode := cbCity.KeyValue;
  //使用filter过滤，只显示city=keycode的数据集
  qryDistrict.Filtered := False;
  qryDistrict.Filter := ‘city=‘+QuotedStr(keycode);
  qryDistrict.Filtered := True;
  //由于有些城市的区域为空，所以要把DBLookupCombobox的enable设置FALSE，否则会报错
  if qryDistrict.RecordCount=0 then
    cbDistrict.Enabled := False
  else
    cbDistrict.Enabled := True;

  //清除已选择的地区的值
  cbDistrict.KeyValue := ‘‘;
end;

城市选择之后

原文地址：https://www.cnblogs.com/Kwong/p/9503315.html