用于在报告进度时以各种格式导出对象的代码，使其更具扩展性

Question

描述

WinForms应用程序具有以各种格式导出以下类型对象的功能：

class Item
{
public int id { get; set; }
public string description { get; set; }
}

单击窗口中的按钮，会显示SaveFileDialog，当前它提供了以.txt、.csv或.xlsx格式保存数据的选项。由于有时有数百或数千个对象，并且UI不应该冻结，因此使用Task来运行此操作。这种实现是可行的，但可以改进。

代码

public partial class ExportWindow : Form
{
// objects to be exported
List<Item> items;
// event handler for the "Export" button click
private async void exportButton_click(object sender, System.EventArgs e)
{
SaveFileDialog exportDialog = new SaveFileDialog();
exportDialog.Filter = "Text File (*.txt)|*.txt|Comma-separated values file (*.csv)|*.csv|Excel spreadsheet (*.xlsx)|*.xlsx";
exportDialog.CheckPathExists = true;
DialogResult result = exportDialog.ShowDialog();
if (result == DialogResult.OK)
{
var ext = System.IO.Path.GetExtension(saveExportFileDlg.FileName);
try
{ 
// update status bar
// (it is a custom control)
statusBar.text("Exporting");
// now export it
await Task.Run(() =>
{
switch (ext.ToLower())
{
case ".txt":
saveAsTxt(exportDialog.FileName);
break;
case ".csv":
saveAsCsv(exportDialog.FileName);
break;

case ".xlsx":
saveAsExcel(exportDialog.FileName);
break;
default:
// shouldn't happen
throw new Exception("Specified export format not supported.");
}
});
}
catch (System.IO.IOException ex)
{
statusBar.text("Export failed");
logger.logError("Export failed" + ex.Message + "n" + ex.StackTrace);
return;
}
}
}
private delegate void updateProgressDelegate(int percentage);
public void updateProgress(int percentage)
{
if (statusBar.InvokeRequired)
{
var d = updateProgressDelegate(updateProgress);
statusBar.Invoke(d, percentage);
}
else
{
_updateProgress(percentage);
}
}
private void saveAsTxt(string filename)
{
IProgress<int> progress = new Progress<int>(updateProgress);

// save the text file, while reporting progress....
}
private void saveAsCsv(string filename)
{
IProgress<int> progress = new Progress<int>(updateProgress);

using (StreamWriter writer = StreamWriter(filename))
{
// write the headers and the data, while reporting progres...
}
}
private void saveAsExcel(string filename)
{
IProgress<int> progress = Progress<int>(updateProgress);
// EPPlus magic to write the data, while reporting progress...
}
}

问题

如何重构它以使其更具可扩展性？也就是说，如果我想添加对更多文件类型的支持，请使修改变得简单快捷。switch语句可能会很长。从本质上讲，如何遵守开放/封闭原则？

Answer 1

为每个扩展创建类可能是一种方法。而不仅仅是通过迭代一些列表或使用反射，所以如果你想添加对新扩展的支持，你必须创建一个新的类，而不是触摸ExportWindow