修复DBGrideh使用TMemTableEh在Footers求平均值为0的Bug

在一个项目中，使用DBGrideh，当使用自带的内存数据集时，对于Footers添加的求平均值，一直显示为0，其他汇总数据都是可以的，而切换使用TClientDataSet或者TADODataSet，所有汇总数据包括平均值都有值。

打开相关部分源码查看了下，发现DBGrideh自带的内存数据集关于汇总平均数这块，竟然没有处理……，什么情况？

原始相关函数：

procedure TCustomMemTableEh.GetAggregatedValuesForRange(FromBM, ToBM: TUniBookmarkEh;
  FieldName: String; var ResultArr: TAggrResultArr; AggrFuncs: TAggrFunctionsEh);
var
  FromRN, ToRN: Integer;
  i: Integer;
  v: Variant;
  VarTypeNum: Integer;
  FieldIndex: Integer;
begin
  ResultArr[agfSumEh] := Null;
  ResultArr[agfCountEh] := 0;
  ResultArr[agfAvg] := Null;
  ResultArr[agfMin] := Null;
  ResultArr[agfMax] := Null;
  if not Active then Exit;
  if FromBM <> NilBookmarkEh then
    if UniBookmarkValid(FromBM)
      then FromRN := UniBookmarkToRecNo(FromBM)
      else Exit
  else
    FromRN := 1;
  if ToBM <> NilBookmarkEh then
    if UniBookmarkValid(ToBM)
      then ToRN := UniBookmarkToRecNo(ToBM)
      else Exit
  else
    ToRN := RecordCount;

  if (FieldName = '') and (AggrFuncs = [agfCountEh]) then
  begin
    for i := FromRN-1 to ToRN-1 do
      ResultArr[agfCountEh] := ResultArr[agfCountEh] + 1;
    Exit;  
  end;

  if FRecordsView.MemTableData.DataStruct.FindField(FieldName) = nil then
    Exit;
  VarTypeNum := FRecordsView.MemTableData.DataStruct.FieldByName(FieldName).GetVarDataType;
  FieldIndex := FRecordsView.MemTableData.DataStruct.FieldIndex(FieldName);
  for i := FromRN-1 to ToRN-1 do
  begin
    v := FRecordsView.RecordView[i].Rec.Value[FieldIndex, dvvValueEh];
    if not VarIsNullEh(v) then
    begin
      if (agfCountEh in AggrFuncs) or (agfAvg in AggrFuncs) then
        ResultArr[agfCountEh] := ResultArr[agfCountEh] + 1;            //当设置求平均值时，此处仅仅做了一次记数累计
      if (VarTypeNum in [varSmallint, varInteger, varSingle, varDouble, varCurrency,
{$IFDEF EH_LIB_6}
         varShortInt, varWord, varInt64, varLongWord,
{$ENDIF}
         varByte, varDate]) or (VarTypeNum = varFMTBcd) then
      begin
        if (agfSumEh in AggrFuncs) and (VarTypeNum <> varDate) then
          if VarIsNullEh(ResultArr[agfSumEh])
            then ResultArr[agfSumEh] := v
            else ResultArr[agfSumEh] := ResultArr[agfSumEh] + v;

        if agfMin in AggrFuncs then
            if VarIsNullEh(ResultArr[agfMin]) then
            ResultArr[agfMin] := v
          else if ResultArr[agfMin] > v then
            ResultArr[agfMin] := v;

        if agfMax in AggrFuncs then
          if VarIsNullEh(ResultArr[agfMax]) then
            ResultArr[agfMax] := v
          else if ResultArr[agfMax] < v then
            ResultArr[agfMax] := v;
      end
    end;
  end;

  if agfMax in AggrFuncs then                //求平均值，此处的触发条件竟然是 agfMax ....
    if not VarIsNullEh(ResultArr[agfSumEh]) then
      ResultArr[agfAvg] := ResultArr[agfSumEh] / ResultArr[agfCountEh];  //此处因为没有在agfAvg时对agfSumEh 求和汇总，该值应为0;
end;

修改方法：

1、打开MemTableEh.pas

2、找到GetAggregatedValuesForRange函数，修改成如下：

procedure TCustomMemTableEh.GetAggregatedValuesForRange(FromBM, ToBM: TUniBookmarkEh;
 FieldName: String; var ResultArr: TAggrResultArr; AggrFuncs: TAggrFunctionsEh);
var
 FromRN, ToRN: Integer;
 i: Integer;
 v: Variant;
 VarTypeNum: Integer;
 FieldIndex: Integer;
begin
 ResultArr[agfSumEh] := Null;
 ResultArr[agfCountEh] := 0;
 ResultArr[agfAvg] := Null;
 ResultArr[agfMin] := Null;
 ResultArr[agfMax] := Null;
 if not Active then Exit;
 if FromBM <> NilBookmarkEh then
  if UniBookmarkValid(FromBM)
   then FromRN := UniBookmarkToRecNo(FromBM)
   else Exit
 else
  FromRN := 1;
 if ToBM <> NilBookmarkEh then
  if UniBookmarkValid(ToBM)
   then ToRN := UniBookmarkToRecNo(ToBM)
   else Exit
 else
  ToRN := RecordCount;


 if (FieldName = '') and (AggrFuncs = [agfCountEh]) then
 begin
  for i := FromRN-1 to ToRN-1 do
   ResultArr[agfCountEh] := ResultArr[agfCountEh] + 1;
  Exit; 
 end;


 if FRecordsView.MemTableData.DataStruct.FindField(FieldName) = nil then
  Exit;
 VarTypeNum := FRecordsView.MemTableData.DataStruct.FieldByName(FieldName).GetVarDataType;
 FieldIndex := FRecordsView.MemTableData.DataStruct.FieldIndex(FieldName);
 for i := FromRN-1 to ToRN-1 do
 begin
  v := FRecordsView.RecordView[i].Rec.Value[FieldIndex, dvvValueEh];
  if not VarIsNullEh(v) then
  begin
   if (agfCountEh in AggrFuncs) or (agfAvg in AggrFuncs) then
    ResultArr[agfCountEh] := ResultArr[agfCountEh] + 1;
   if (VarTypeNum in [varSmallint, varInteger, varSingle, varDouble, varCurrency,
{$IFDEF EH_LIB_6}
    varShortInt, varWord, varInt64, varLongWord,
{$ENDIF}
    varByte, varDate]) or (VarTypeNum = varFMTBcd) then
   begin
    if ((agfSumEh in AggrFuncs) or (agfAvg in AggrFuncs)) and (VarTypeNum <> varDate) then  //此处修改
     if VarIsNullEh(ResultArr[agfSumEh])
      then ResultArr[agfSumEh] := v
      else ResultArr[agfSumEh] := ResultArr[agfSumEh] + v;


    if agfMin in AggrFuncs then
        if VarIsNullEh(ResultArr[agfMin]) then
      ResultArr[agfMin] := v
     else if ResultArr[agfMin] > v then
      ResultArr[agfMin] := v;


    if agfMax in AggrFuncs then
     if VarIsNullEh(ResultArr[agfMax]) then
      ResultArr[agfMax] := v
     else if ResultArr[agfMax] < v then
      ResultArr[agfMax] := v;
   end
  end;
 end;


 if agfAvg in AggrFuncs then    //此处修改
  if not VarIsNullEh(ResultArr[agfSumEh]) then
   ResultArr[agfAvg] := ResultArr[agfSumEh] / ResultArr[agfCountEh];
end;