TClientDataSet[1]: 浏览测试数据

希望这次学习能对其内存协调方式有所了解, 顺便学点数据库的知识.

TClientDataSet 是一个内存数据集(说”数据表”对不住它), 其内存数据可存取到本地(.cds 或 .xml 格式).

用 TDBGrid 可方便查看其内存数据, 但需要用数据源组件(如: TDataSource)桥接一下:

TDBGrid.DataSource ← TDataSource.DataSet ← TClientDataSet

Program Files\Common Files\CodeGear Shared\Data 下有官方提供的测试数据, 下面程序可浏览这些数据:

//假定已在设计时挂接好: ClientDataSet1、DataSource1、DBGrid1, 并添加一个 ListBox1

uses IOUtils, Types;

var DataPath: string;

procedure TForm1.FormCreate(Sender: TObject);

var

sArr: TStringDynArray;

s: string;

begin

{ 获取测试数据所在的路径 }

DataPath := GetEnvironmentVariable(‘COMMONPROGRAMFILES’) + ‘\CodeGear Shared\Data\’;

{ 获取路径下所有 cds 文件 }

sArr := TDirectory.GetFiles(DataPath, ‘*.cds’);

{ 添加到列表 }

for s in sArr do ListBox1.Items.Add(ExtractRelativePath(DataPath, s));

end;

procedure TForm1.ListBox1Click(Sender: TObject);

begin

ClientDataSet1.LoadFromFile(DataPath + ListBox1.Items[ListBox1.ItemIndex]);

end;

其中的:

procedure TForm1.ListBox1Click(Sender: TObject);

begin

ClientDataSet1.LoadFromFile(DataPath + ListBox1.Items[ListBox1.ItemIndex]);

end;

//可换成:

procedure TForm1.ListBox1Click(Sender: TObject);

begin

ClientDataSet1.Active := False;

ClientDataSet1.FileName := DataPath + ListBox1.Items[ListBox1.ItemIndex];

ClientDataSet1.Active := True;

end;

//或换成:

procedure TForm1.ListBox1Click(Sender: TObject);

begin

ClientDataSet1.Close;

ClientDataSet1.FileName := DataPath + ListBox1.Items[ListBox1.ItemIndex];

ClientDataSet1.Open;

end;

从源码中看 Open/Close 方法和 Active 属性的关系:

{ TClientDataSet 的继承关系: TDataSet - TCustomClientDataSet - TClientDataSet }

procedure TDataSet.Open;

begin

Active := True;

end;

procedure TDataSet.Close;

begin

Active := False;

end;

从源码中查看 LoadFromFile 对 Open/Close 方法的调用:

procedure TCustomClientDataSet.LoadFromFile(const FileName: string = ”);

var

Stream: TStream;

begin

Close;

…

LoadFromStream(Stream); { LoadFromFile 调用了 LoadFromStream}

…

end;

procedure TCustomClientDataSet.LoadFromStream(Stream: TStream);

begin

Close;

ReadDataPacket(Stream, False);

Open;

end;