如何在TcxExtLookupComboBox中使用TcxCustomDataSource？ [英] How to use a TcxCustomDataSource in a TcxExtLookupComboBox?

问题描述

我使用来自Devexpress的TcxExtLookupComboBox并尝试实现自定义数据源。我已经这样设置了customdatasource：

I use a TcxExtLookupComboBox from Devexpress and try to implement a custom datasource. I have set the customdatasource like this:

procedure TMainForm.FormCreate(Sender: TObject);
begin
  fDataSource := TMyDataSource.Create;
  cbotestSearch.Properties.View.DataController.CustomDataSource := fDataSource;
end;

TMyDataSource在这里定义：

TMyDataSource is defined here:

unit Datasource;

interface

uses
  Classes,
  IBQuery,
  SysUtils,
  cxCustomData;

type
  TSearchItem = class
    private
      BoldID: String;
      Display: String
  end;

  TMyDataSource = class(TcxCustomDataSource)
  private
    fSearchList: TList;
  protected
    function GetRecordCount: Integer; override;
    function GetValue(ARecordHandle: TcxDataRecordHandle; AItemHandle: TcxDataItemHandle): Variant; override;
  public
    constructor Create;
    destructor Destroy; override;
    procedure GetData;
  end;

implementation

constructor TMyDataSource.Create;
begin
  inherited Create;
  fSearchList := TList.Create;
end;

destructor TMyDataSource.Destroy;
begin
  FreeAndNil(fSearchList);
  inherited;
end;

procedure TMyDataSource.GetData;
var
  vItem: TSearchItem;
begin
  fSearchList.Clear;

  vItem := TSearchItem.Create;
  vItem.BoldID  := '1000';
  vItem.Display := 'test';
  fSearchList.Add(vItem);

  vItem := TSearchItem.Create;
  vItem.BoldID  := '1100';
  vItem.Display := 'test2';
  fSearchList.Add(vItem);

  DataChanged;    // Don't do anything as provider is nil
end;

function TMyDataSource.GetRecordCount: Integer;
begin
  // Is never entered
  Result := fSearchList.Count;
end;

function TMyDataSource.GetValue(ARecordHandle: TcxDataRecordHandle;
  AItemHandle: TcxDataItemHandle): Variant;
begin
  // Is never entered
  Result := 'Test';
end;

end.

问题是从不调用TMyDataSource.GetValue。任何提示如何解决？

The problem is that TMyDataSource.GetValue is never called. Any hint how to fix ?

更新1：我在这里还有另一个提示。如果我单步执行应该导致GetValue调用的DataChanged方法，则如下所示：

Update 1: I have another hint here. If I single step in the DataChanged method that should cause GetValue to be called is looks like this:

procedure TcxCustomDataSource.DataChanged;
begin
  if Provider = nil then Exit;

  // Code using Provider
end;

，在这种情况下，提供者为零。但是，正如您所见，我已将数据源分配为oncreate形式。

and Provider is nil in this case. But I have assigned the Datasource in Forms oncreate as you see.

推荐答案

cxExtLookupComboBox仅可用于DB〜视图。这样的视图不能接受TcxCustomDataSource对象的实例作为数据源。因此，您的代码将不起作用:-(。将来有实现此功能的建议，并且它已在以下位置注册：

cxExtLookupComboBox can only work with DB~views. Such views cannot accept instances of the TcxCustomDataSource object as a DataSource. So, your code will not work :-(. There is a suggestion to implement this feature in the future and it is registered at:

http://www.devexpress.com/Support/Center/ViewIssue.aspx?issueid=AS10025

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