TClientDataSet.AppendData原因「正在嘗試數據追加到非局部數據集」錯誤

Question

當執行下面的代碼：

var S, D: TClientDataSet; 
    P: TDataSetProvider; 
    i: integer; 
begin 
    S := TClientDataSet.Create(nil); 
    D := TClientDataSet.Create(nil); 
    P := TDataSetProvider.Create(nil); 
    try 
    S.FieldDefs.Add('F1', ftString, 20); 
    S.FieldDefs.Add('F2', ftBcd,  2); 
    S.FieldDefs.Add('F3', ftBoolean); 
    S.CreateDataSet; 
    S.AppendRecord(['Test 1', 1, True]); 
    S.AppendRecord(['Test 2', 2, False]); 
    S.First; 
    S.MergeChangeLog; 

    D.FieldDefs.Add('F1', ftString, 20); 
    D.FieldDefs.Add('F2', ftBcd,  2); 
    D.FieldDefs.Add('F3', ftBoolean); 
    D.CreateDataSet; 

    P.DataSet := S; 
    D.SetProvider(P); 
    D.AppendData(P.GetRecords(-1, i, MetaDataOption), False); 
    finally 
    S.Free; 
    D.Free; 
    P.Free; 
    end; 
end; 

例外，提示「正在嘗試數據追加到非局部數據集」。

但是，下面的代碼工作：

var S, D: TClientDataSet; 
    P: TDataSetProvider; 
    i: integer; 
begin 
    S := TClientDataSet.Create(nil); 
    D := TClientDataSet.Create(nil); 
    P := TDataSetProvider.Create(nil); 
    try 
    S.FieldDefs.Add('F1', ftString, 20); 
    S.FieldDefs.Add('F2', ftBcd,  2); 
    S.FieldDefs.Add('F3', ftBoolean); 
    S.CreateDataSet; 
    S.AppendRecord(['Test 1', 1, True]); 
    S.AppendRecord(['Test 2', 2, False]); 
    S.First; 
    S.MergeChangeLog; 

    // The 4 lines below that were in the first code sample are omitted here 
    //D.FieldDefs.Add('F1', ftString, 20); 
    //D.FieldDefs.Add('F2', ftBcd,  2); 
    //D.FieldDefs.Add('F3', ftBoolean); 
    //D.CreateDataSet; 

    D.Data := S.Data; // This line does not appear in the first code sample 

    P.DataSet := S; 
    D.SetProvider(P); 
    D.AppendData(P.GetRecords(-1, i, MetaDataOption), False); 
    finally 
    S.Free; 
    D.Free; 
    P.Free; 
    end; 
end; 

Answer 1

從你的第一個代碼刪除D.CreateDataSet;，你會被罰款。看起來數據集在調用CreateDataSet時不接受任何部分更新。

procedure TForm7.Button3Click(Sender: TObject); 
var S, D: TClientDataSet; 
    P: TDataSetProvider; 
    i: integer; 
begin 
    S := TClientDataSet.Create(nil); 
    D := TClientDataSet.Create(nil); 
    P := TDataSetProvider.Create(nil); 
    try 
    S.FieldDefs.Add('F1', ftString, 20); 
    S.FieldDefs.Add('F2', ftBcd,  2); 
    S.FieldDefs.Add('F3', ftBoolean); 
    S.CreateDataSet; 
    S.AppendRecord(['Test 1', 1, True]); 
    S.AppendRecord(['Test 2', 2, False]); 
    S.First; 

    P.DataSet := S; 
    D.SetProvider(P); 
    D.AppendData(P.GetRecords(-1, i, MetaDataOption), False); 
    finally 
    S.Free; 
    D.Free; 
    P.Free; 
    end; 
end;