C#中如何调用Delphi写的Dll

#region 定义调用Delphi写的画图DLL 
///  
/// 定义调用Delphi写的画图DLL 
///  
private class DrawChartFromDll 
{ 
//定义DLL文件名，此文件路径要加到系统Path中 
private const string _fileDll = @"Chart.dll"; 
//调用非托管Dll，GetChartFromXMLByNet是ChartAccess.dll公开的函数名称 
[DllImport(_fileDll, EntryPoint = "GetChartFromXMLByNet", 
CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)] 
//C#中的申明 
public static extern int GetChartFromXMLByNet(int piChartType, 
string psXMLFileName, string psPriChartFileName, string psSecChartFileName, 
string psPriHotFileName, string psSecHotFileName); 
} 
#endregion 
public ChartResultData GetCharts(ChartData _ChartData, 
Hashtable _HotPriAdditionSeqNo, Hashtable _HotSecAdditionSeqNo) 
{ 
//根据数据生成XML文件 
string _xmlFileName = ""; 
ChartResultData _ChartResultData = new ChartResultData(); 
try 
{ 
_xmlFileName = this.ConvertDataToXml(_ChartData); 
} 
catch (Exception err) 
{ 
_ChartResultData.ErrMessage = err.Message; 
} 
... 
//调用DELPHI，取得返回参数 
int _return = -1; 
try 
{ 
_return = DrawChartFromDll.GetChartFromXMLByNet(m_chartType, _xmlFileName,
_priChartFileName, _secChartFileName, _priHotFileName, _secHotFileName); 
} 
catch (Exception err) 
{ 
if (_return > 0) 
{ 
//删除临时生成的XML文件 
this.DeleteTempFile(_xmlFileName); 
this.DeleteTempFile(_priChartFileName); 
this.DeleteTempFile(_secChartFileName); 
this.DeleteTempFile(_priHotFileName); 
this.DeleteTempFile(_secHotFileName); 
_ChartResultData.ErrMessage = err.Message; 
return _ChartResultData; 
} 
else 
{ 
//可能因为安全性问题，在频繁连续调用DLL方法时有可能出现內存保护错误信息，虽然出错，
但方法已经正确调用并能返回正确的值，此时可以忽略此错误
_return = 0; 
} 
} 
//删除临时生成的XML文件 
this.DeleteTempFile(_xmlFileName); 
... 
}

function GetChartFromXMLByNet(piChartType: integer; psXMLFileName: PChar; 
psPriChartFileName: PChar; psSecChartFileName: PChar; out psPriHotMsg: PChar; 
out psSecHotMsg: PChar): integer; stdcall;export;