C# Cookbook, Second Edition

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• C# Cookbook, Second Edition

• By: Jay Hilyard; Stephen Teilhet

• Publisher: O'Reilly Media, Inc.

• Pub. Date: January 30, 2006   Most Recent Edition

• Print ISBN-13: 978-0-596-10063-6

• Print ISBN-10: 0-596-10063-9

• Pages in Print Edition: 1192

• Subscriber Rating: [0 Ratings]

  
  

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关键词：Cookbook Edition Second dition editio Stephen Media

Recipe 3.1. Creating Union-Type Structures
Problem
You need to create a data type that behaves like a union type in C++. A union type is useful mainly in interop scenarios in which the unmanaged code accepts and/or returns a union type; we suggest that you do not use it in other situations.

Solution
Use a structure and mark it with the StructLayout attribute (specifying the LayoutKind.Explicit layout kind in the constructor). In addition, mark each field in the structure with the FieldOffset attribute. The following structure defines a union in which a single signed numeric value can be stored:

1. using System.Runtime.InteropServices;
   
2.         [StructLayoutAttribute(LayoutKind.Explicit)]
   
3.         struct SignedNumber
   
4.         {
   
5.            [FieldOffsetAttribute(0)]
   
6.            public sbyte Num1;
   
7.            [FieldOffsetAttribute(0)]
   
8.            public short Num2;
   
9.            [FieldOffsetAttribute(0)]
   
10.            public int Num3;
    
11.            [FieldOffsetAttribute(0)]
    
12.            public long Num4;
    
13.            [FieldOffsetAttribute(0)]
    
14.            public float Num5;
    
15.            [FieldOffsetAttribute(0)]
    
16.            public double Num6;
    
17.            [FieldOffsetAttribute(0)]
    
18.            public decimal Num7;
    
19.         }

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1. The next structure is similar to the SignedNumber structure, except that it can contain a String type in addition to the signed numeric value:
   
2. 
   
3.         [StructLayoutAttribute(LayoutKind.Explicit)]
   
4.         struct SignedNumberWithText
   
5.         {
   
6.            [FieldOffsetAttribute(0)]
   
7.            public sbyte Num1;
   
8.            [FieldOffsetAttribute(0)]
   
9.            public short Num2;
   
10.            [FieldOffsetAttribute(0)]
    
11.            public int Num3;
    
12.            [FieldOffsetAttribute(0)]
    
13.            public long Num4;
    
14.            [FieldOffsetAttribute(0)]
    
15.            public float Num5;
    
16.            [FieldOffsetAttribute(0)]
    
17.            public double Num6;
    
18.            [FieldOffsetAttribute(0)]
    
19.            public decimal Num7;
    
20.            [FieldOffsetAttribute(16)]
    
21.            public string Text1;
    
22.         }

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Recipe 3.2. Allowing a Type to Represent Itself as a String
Problem
Your class or structure needs to control how its information is displayed when its ToString method is called. In addition, you need to apply different formats to this information. For example, when creating a new data type, such as a Line class, you might want to allow objects of this type to be able to display themselves in a textual format. In the case of a Line object, it might display itself as (x1, y1)(x2, y2).

Solution
Override and/or implement the IFormattable.ToString method to display numeric information, such as for a Line structure:

1. using System;
   
2.         using System.Text;
   
3.         using System.Text.RegularExpressions;
   
4. 
   
5.         public struct Line : IFormattable
   
6.         {
   
7.            public Line(int startX, int startY, int endX, int endY)
   
8.            {
   
9.               x1 = startX;
   
10.               x2 = endX;
    
11.               y1 = startY;
    
12.               y2 = endY;
    
13.            }
    
14.            public int x1;
    
15.            public int y1;
    
16.            public int x2;
    
17.            public int y2;
    
18. 
    
19.            public double GetDirectionInRadians( )
    
20.            {
    
21.               int xSide = x2 - x1;
    
22.               int ySide = y2 - y1;
    
23.               if (xSide == 0) // Prevent divide-by-zero.
    
24.                     return (0);
    
25.               else
    
26.                     return (Math.Atan (ySide / xSide));
    
27.            }
    
28.            public double GetMagnitude( )
    
29.            {
    
30.               int xSide = x2 - x1;
    
31.               int ySide = y2 - y1;
    
32.               return ( Math.Sqrt((xSide * xSide) + (ySide * ySide)));
    
33.            }
    
34. 
    
35.            // This overrides the Object.ToString method.
    
36.            // This override is not required for this recipe
    
37.            // and is included for completeness.
    
38.            public override string ToString( )
    
39.            {
    
40.               return (String.Format("({0},{1}) ({2},{3})", x1, y1, x2, y2));
    
41.            }
    
42.            public string ToString(string format)
    
43.            {
    
44.               return (this.ToString(format, null));
    
45.            }
    
46.            public string ToString(IFormatProvider formatProvider)
    
47.            {
    
48.               return (this.ToString(null, formatProvider));
    
49.            }
    
50.            public string ToString(string format, IFormatProvider formatProvider)
    
51.            {
    
52.               StringBuilder compositeStr = new StringBuilder("");
    
53.               if ((format != null) && (format.ToUpper( ).Equals("V")))
    
54.               {
    
55.                     double direction = this.GetDirectionInRadians( );
    
56.                     double magnitude = this.GetMagnitude( );
    
57.                     string retStringD = direction.ToString("G5", formatProvider);
    
58.                     string retStringM = magnitude.ToString("G5", formatProvider);
    
59.                     compositeStr.Append("magnitude = ").Append(retStringM).Append
    
60.                             ("\tDirection = ").Append(retStringD);
    
61.               }
    
62.               else
    
63.               {
    
64.                     string retStringX1 = this.x1.ToString(format, formatProvider);
    
65.                     string retStringY1 = this.y1.ToString(format, formatProvider);
    
66.                     string retStringX2 = this.x2.ToString(format, formatProvider);
    
67.                     string retStringY2 = this.y2.ToString(format, formatProvider);
    
68.                     compositeStr.Append("(").Append(retStringX1).Append(",").Append
    
69.                           (retStringY1).Append(")(").Append(retStringX2).Append
    
70.                           (",").Append(retStringY2).Append(")");
    
71.               }
    
72.               return (compositeStr.ToString( ));
    
73.            }
    
74.         }

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Recipe 3.3. Converting a String Representation of an Object into an Actual Object
Problem
You need a way of accepting a string containing a textual representation of an object and converting it to an object usable by your application. For example, if you were provided with the string representation of a line (x1, y1)(x2, y2), you would want to convert it into a Line structure.

Solution
Implement a Parse method on your Line structure:

1. using System;
   
2.         using System.Text;
   
3.         using System.Text.RegularExpressions;
   
4.         public struct Line : IFormattable
   
5.         {
   
6.            public Line(int startX, int startY, int endX, int endY)
   
7.            {
   
8.            x1 = startX;
   
9.            x2 = endX;
   
10.            y1 = startY;
    
11.            y2 = endY;
    
12.         }
    
13.         public int x1;
    
14.         public int y1;
    
15.         public int x2;
    
16.         public int y2;
    
17.         public override bool Equals(object obj)
    
18.         {
    
19.            bool isEqual = false;
    
20.            if (obj == null || (this.GetType() != obj.GetType( )))
    
21.            {
    
22.               isEqual = false;
    
23.            }
    
24.            else
    
25.            {
    
26.               Line theLine = (Line)obj;
    
27.               isEqual = (this.x1 == theLine.x1) &&
    
28.                (this.y1 == theLine.y1) &&
    
29.                (this.x2 == theLine.x2) &&
    
30.                (this.y2 == theLine.y2);
    
31.            }
    
32.            return (isEqual);
    
33.         }
    
34.         public bool Equals(Line lineObj)
    
35.         {
    
36.            bool isEqual = (this.x1 == lineObj.x1) &&
    
37.             (this.y1 == lineObj.y1) &&
    
38.             (this.x2 == lineObj.x2) &&
    
39.             (this.y2 == lineObj.y2);
    
40.             return (isEqual);
    
41.         }
    
42.         public override int GetHashCode()
    
43.         {
    
44.            return ((x1 + x2) ^ (y1 + y2));
    
45.         }
    
46.         public static Line Parse(string stringLine)
    
47.         {
    
48.            if (stringLine == null)
    
49.            {
    
50.               throw (new ArgumentNullException(
    
51.                        "stringLine",
    
52.                        "A null cannot be passed into the Parse method."));
    
53.            }
    
54.            // Take this string (x1,y1)(x2,y2) and convert it to a Line object.
    
55.            int X1 = 0;
    
56.            int Y1 = 0;
    
57.            int X2 = 0;
    
58.            int Y2 = 0;
    
59.            MatchCollection MC = Regex.Matches(stringLine,
    
60.               @"\s*\(\s*(?<x1>\d+)\s*\,\s*(?<y1>\d+)\s*\)\s*\(\s*(?<x2>" +
    
61.               @"\d+)\s*\,\s*(?<y2>\d+)\s*\)" );
    
62.            if (MC.Count == 1)
    
63.            {
    
64.               Match M = MC[0];
    
65.               X1 = int.Parse(M.Groups["x1"].Value);
    
66.               Y1 = int.Parse(M.Groups["y1"].Value);
    
67.               X2 = int.Parse(M.Groups["x2"].Value);
    
68.               Y2 = int.Parse(M.Groups["y2"].Value);
    
69.            }
    
70.            else
    
71.            {
    
72.               throw (new ArgumentException("The value " + stringLine +
    
73.                                            " is not a well formed Line value."));
    
74.            }
    
75.            return (new Line(X1, Y1, X2, Y2));
    
76.         }
    
77.         public double GetDirectionInRadians()
    
78.         {
    
79.            int xSide = x2 - x1;
    
80.            int ySide = y2 - y1;
    
81.            if (xSide == 0) // Prevent divide-by-zero.
    
82.               return (0);
    
83.            else
    
84.               return (Math.Atan (ySide / xSide));
    
85.         }
    
86.         public double GetMagnitude()
    
87.         {
    
88.            int xSide = x2 - x1;
    
89.            int ySide = y2 - y1;
    
90.            return (Math.Sqrt( Math.Sqrt((xSide * xSide) + (ySide * ySide))));
    
91.         }
    
92.         public override string ToString()
    
93.         {
    
94.            return (String.Format("({0},{1}) ({2},{3})", x1, y1, x2, y2));
    
95.         }
    
96.         public string ToString(string format)
    
97.         {
    
98.            return (this.ToString(format, null));
    
99.         }
    
100.         public string ToString(IFormatProvider formatProvider)
     
101.         {
     
102.            return (this.ToString(null, formatProvider));
     
103.         }
     
104.         public string ToString(string format, IFormatProvider formatProvider)
     
105.         {
     
106.            StringBuilder compositeStr = new StringBuilder("");
     
107.            if ((format != null) && (format.ToUpper().Equals("V")))
     
108.            {
     
109.               double direction = this.GetDirectionInRadians();            
     
110.               double magnitude = this.GetMagnitude();
     
111.               string retStringD = direction.ToString("G5", formatProvider);
     
112.               string retStringM = magnitude.ToString("G5", formatProvider);
     
113.               compositeStr.Append(
     
114.                     "magnitude = ").Append(retStringM).Append(
     
115.                                 "\tDirection = ").Append(retStringD);
     
116.            }
     
117.            else
     
118.            {
     
119.               string retStringX1 = this.x1.ToString(format, formatProvider);
     
120.               string retStringY1 = this.y1.ToString(format, formatProvider);
     
121.               string retStringX2 = this.x2.ToString(format, formatProvider);
     
122.               string retStringY2 = this.y2.ToString(format, formatProvider);
     
123.               compositeStr.Append("(").Append(retStringX1).Append(",").Append(
     
124.                     retStringY1).Append(")(").
     
125.                        Append(retStringX2).Append(",").Append(
     
126.                           retStringY2).Append(")");
     
127.               }
     
128.               return (compositeStr.ToString());
     
129.            }
     
130.         }

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