Read Fixed-Width Text Records using C#

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雖然使用純文字檔格式(Flat File)來交換資料並不是很好的方式,然而在 XML 盛行的今日它仍是普遍存在的資料交換格式。純文字檔格式的資料列通常以特定的符號區隔,或是固定寬度欄位來區隔不同資料欄位。從程式員的觀點來看,處理固定寬度欄位格式的資料並不如使用特定的符號區隔的格式來得輕鬆。如果是使用傳統的方式從「位置」擷取資料,那將會更加麻煩。所以,本文在這裡就要介紹幾種處理固定寬度格式資料的解決方案。

以下範例文字檔內容是以固定寬度格式所描述的銷售訂單內容:
0001S0000120081101       2     5000
0001S0000220081101 10 2500
0001S0000320081101 1 10500

其檔案格式內容定義如下:
欄位名稱欄位長度
銷售店代號X(4)
訂單編號X(6)
訂單日期X(8)
銷售量9(8)
銷售金額9(9)

LINQ to Text Files
首先必須先定義一個延伸方法(Extension Method)來逐行讀取資料流,並建立可以供 LINQ 查詢的可列舉集合。在此我引用了 Eric White 在 LINQ to Text Files 中所提供的 StreamReaderSequence 類別:
public static class StreamReaderSequence
{
public static IEnumerable<string> Lines(this StreamReader source)
{
String line;

if (source == null)
throw new ArgumentNullException("source");
while ((line = source.ReadLine()) != null)
{
yield return line;
}
}
}

接下來使用規則運算式(Regular expression)依序定義群組編號及資料欄位長度:
Regex re = new Regex("^(?<1>.{4})" +
"(?<2>.{6})" +
"(?<3>.{8})" +
"(?<4>.{8})" +
"(?<5>.{9})",
RegexOptions.Compiled);

接著再搭配 LINQ 語法的 let 子句取得規則運算式比對所擷取的群組集合,然後併入查詢結果中:
using (StreamReader sr = new StreamReader(@"d:\orders.txt"))
{
var orders =
from line in sr.Lines()
let fields = re.Match(line).Groups
select new
{
StoreID = fields[1].Value.Trim(),
OrderNumber = fields[2].Value.Trim(),
OrderDate = DateTime.ParseExact(fields[3].Value.Trim(),
"yyyyMMdd", CultureInfo.InvariantCulture),
Quantity = int.Parse(fields[4].Value),
Amount = int.Parse(fields[5].Value)
};

foreach (var order in orders)
{
Console.WriteLine("{0},{1},{2},{3},{4}",
order.StoreID,
order.OrderNumber,
order.OrderDate,
order.Quantity,
order.Amount
);
}
}

LINQ to SQL
Microsoft OLE DB Provider for Jet 可用來存取及查詢文字檔,但必須在文字檔的相同目錄中建立 Schema.ini 檔來描述文字檔的結構:
[orders.txt]
Format=FixedLength
ColNameHeader=False
MaxScanRows=0
Col1=StoreID Text Width 4
Col2=OrderNumber Text Width 6
Col3=OrderDate DateTime Width 8
Col4=Quantity Long Width 8
Col5=Amount Long Width 9
DateTimeFormat=yyyyMMdd

然後,再定義一個資料結構對應的類別:
public class Order
{
public string StoreID;
public string OrderNumber;
public DateTime OrderDate;
public int Quantity;
public int Amount;
}

使用 DataContext 物件透過資料庫連接直接執行 SQL 查詢,並傳回資料結構對應的物件集合。
string filePath = @"d:\orders.txt";
string connString = string.Format( @"Provider=Microsoft.Jet.OLEDB.4.0;" +
"Data Source={0};" +
"Extended Properties='text;HDR=No;Format=FixedLength'",
Path.GetDirectoryName(filePath));

OleDbConnection conn = new OleDbConnection(connString);
DataContext db = new DataContext(conn);

string cmdText = string.Format("SELECT * FROM {0}",
Path.GetFileName(filePath).Replace(".", "#"));
var orders = db.ExecuteQuery<Order>(cmdText);

foreach (var order in orders)
{
Console.WriteLine("{0},{1},{2},{3},{4}",
order.StoreID,
order.OrderNumber,
order.OrderDate,
order.Quantity,
order.Amount
);
}

FileHelpers Library
FileHelpers 是一個用來處理符號區隔或是固定寬度資料的免費類別庫。使用前,你首先必須先定義一個資料結構對應的類別:
[FixedLengthRecord]
public class Order
{
[FieldFixedLength(4)]
public string StoreID;

[FieldFixedLength(6)]
public string OrderNumber;

[FieldFixedLength(8)]
[FieldConverter(ConverterKind.Date, "yyyyMMdd")]
public DateTime OrderDate;

[FieldFixedLength(8)]
[FieldTrim(TrimMode.Left)]
public int Quantity;

[FieldFixedLength(9)]
[FieldTrim(TrimMode.Left)]
public int Amount;
}

然後,透過 FileHelperEngine 讀取資料檔就會自動建立對應的物件陣列。
FileHelperEngine engine = new FileHelperEngine(typeof(Order));          
Order[] orders = engine.ReadFile(@"d:\orders.txt") as Order[];

foreach (var order in orders)
{
Console.WriteLine("{0},{1},{2},{3},{4}",
order.StoreID,
order.OrderNumber,
order.OrderDate,
order.Quantity,
order.Amount
);
}


參考資料:
LINQ TO Text Files by Eric White

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使用 C# 產生網頁縮圖

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在 Web 2.0 網站中,我們常可以看到分享文章或是推薦網站的快照縮圖(Snapshot Thumbnail),來供使用者預覽。如果要在 .NET 中要實做網頁快照,你可以使用 WebBrowser 控制項來達成。在本文中將會示範如何建立 Windows 應用程式來擷取網頁快照並產生縮圖。
snap

範例程式碼
using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;

namespace SnapExample
{
public partial class MainForm : Form
{
private WebPageSnapshot _wps = new WebPageSnapshot(1024, 768);

public MainForm()
{
InitializeComponent();
_wps.ImageCompleted += new ImageCompletedEventHandler(RefreshImage);
}

private void uxGo_Click(object sender, EventArgs e)
{
EnableButtons(false);
_wps.GenerateAsync(uxUrl.Text);
}

private void uxSaveAs_Click(object sender, EventArgs e)
{
uxSaveFileDialog.DefaultExt = "jpg";
uxSaveFileDialog.AddExtension = true;
uxSaveFileDialog.Filter = "JPEG(*.jpg)|*.jpg";
uxSaveFileDialog.ShowDialog(this);

string fileName = uxSaveFileDialog.FileName;
if (fileName != string.Empty)
{
uxThumbnail.BackgroundImage.Save(fileName);
}
}

private void RefreshImage(Image image)
{
decimal sizeRatio = ((decimal)image.Height / image.Width);

int thumbWidth = 100;
int thumbHeight = decimal.ToInt32(sizeRatio * thumbWidth);

Image thumb = image.GetThumbnailImage(
thumbWidth, thumbHeight,
() => false,
IntPtr.Zero
);

if (WebPageSnapshot.IsBlank((Bitmap)thumb))
{
using (Graphics g = Graphics.FromImage(thumb))
{
StringFormat format = new StringFormat();
format.Alignment = StringAlignment.Center;
format.LineAlignment = StringAlignment.Center;
g.DrawString(
"IMAGE NOT AVAILABLE",
new Font("Tahoma", 65),
Brushes.DarkGray,
new RectangleF(0, 0, thumbWidth, thumbHeight),
format
);
}
}

uxThumbnail.BackgroundImage = thumb;

EnableButtons(true);
}

private void EnableButtons(bool enabled)
{
uxSaveAs.Enabled = enabled;
}

private void uxCancel_Click(object sender, EventArgs e)
{
_wps.CancelAsync();
}
}
}

WebPageSnapshot 是一個以 WebBrowse 類別為對象的自訂外覆類別(Wrapper Class)。透過非同步呼叫 GenerateAsync 方法,會將網頁載入到內部隱含的 WebBrowser 實例中。當 WebBrowser 完整載入網頁後,便會呼叫其 DrawToBitmap 方法建立網頁快照的點陣圖,然後引發 ImageCompleted 事件傳回快照圖。在上例中,將會由 RefreshImage 程序來處理 ImageCompleted 事件,並藉由傳入的 Image 物件的 GetThumbnailImage 方法建立縮圖影像。

不過,在測試過程中發現偶會有擷取到空白影像的情況。為了能處理此例外狀況,我從這裡找來了辨識空白圖片的程式演算法,並引用到 WebPageSnapshot 類別的 IsBlank 靜態方法。在範例中,我就對空白截圖繪製了 "IMAGE NOT AVAILABLE" 的字樣。
no image

Download source code

參考資料:
Algorithm to Detect Blank Images by Chinh Do
Event-based Asynchronous Pattern Overview by Microsoft

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ASP.NET Image Uploading with Resizing

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當你使用 ASP.NET 建立上傳圖檔的應用程式時,除了要決定寫入檔案系統或是儲存到資料庫外,你可能還會需要依照原圖的尺寸比例來調整圖片的大小,以符合系統的需求。本文範例程式碼將透過 Image 及 Bitmap 類別,對上傳的原圖進行比例縮放,並以 JPEG 圖檔格式存儲。

<%@ Page Language="C#" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="Drawing=System.Drawing" %>
<script runat="server">
const string _uploadFolder = "~/images/";
const int _maxThumbWidth = 100;

protected void uxUpload_Click(object sender, EventArgs e)
{
if (uxImageFile.HasFile)
{
if (IsValidImage(uxImageFile.FileName))
{
string thumbPath = _uploadFolder +
Path.ChangeExtension(Path.GetRandomFileName(), ".jpg");

using (Drawing::Image image =
Drawing::Image.FromStream(uxImageFile.PostedFile.InputStream))
{
decimal sizeRatio = ((decimal)image.Height / image.Width);
int thumbWidth = _maxThumbWidth;
int thumbHeight = decimal.ToInt32(sizeRatio * thumbWidth);

using (Drawing::Bitmap bitmap =
new Drawing::Bitmap(image, new Drawing::Size(thumbWidth, thumbHeight)))
{
bitmap.Save(Server.MapPath(thumbPath),
Drawing::Imaging.ImageFormat.Jpeg);
}
}
uxThumbImage.ImageUrl = thumbPath;
}
else
{
// This type of file is not allowed.
uxThumbImage.ImageUrl = string.Empty;
}
}
}

public bool IsValidImage(string path)
{
return Regex.IsMatch(path, @"(.*?)\.(gif|jpg|jpeg|png)$", RegexOptions.IgnoreCase);
}
</script>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Image Upload and Resize</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:FileUpload ID="uxImageFile" runat="server" /><br/>
<asp:Button ID="uxUpload" runat="server"
Text="Upload" onclick="uxUpload_Click" /><br/>
<asp:Image ID="uxThumbImage" runat="server"
onerror="javascript:this.style.display='none';" />
</div>
</form>
</body>
</html>

參考資料:
Create High Quality Thumbnail - Resize Image Dynamically - ASP .Net C# Code

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