free code 39 barcode generator c# 7: Behavioral Patterns: Strategy, State, and Template Method in C#.NET

Create ANSI/AIM Code 39 in C#.NET 7: Behavioral Patterns: Strategy, State, and Template Method

7: Behavioral Patterns: Strategy, State, and Template Method
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40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 // Plots the index x against the value val of all elements in the list // IEnumerable<T>.Count is an extension int listSize = list.Count( ); int x = 0; foreach (T item in list) { // val must be a nullable integer. The as operator will return null // if it cannot convert the item to int int val = item as int ; if (!val.HasValue) val = 0; // Drawing methods do not handle nullable types b.SetPixel(x + 20, 20 + 200 - ((int)val), Color.Black); x++; } this.Refresh( ); Thread.Sleep(100); Application.DoEvents( ); } // The Context void ButtonClick(object sender, EventArgs e) { Button control = sender as Button; SortStrategy<T> strategy = null; switch (control.Name) { case "LargeItems": strategy = new MergeSorter<T>( ); break; case "SmallItems": strategy = new QuickSorter<T>( ); break; case "ReversedList": strategy = new MergeSorter<T>( ); break; } IEnumerable<T> newlist = Generator( ); DrawGraph(newlist); if (strategy == null) return; // DrawGraph will be invoked during sorting when // the UpdateUI event is triggered strategy.UpdateUI += new Action<IEnumerable<T>>(DrawGraph); strategy.Sort(newlist); } } // Strategy interface interface SortStrategy<T> where T : IComparable<T> { event Action<IEnumerable<T>> UpdateUI;
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Strategy Pattern |
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92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 void Sort(IEnumerable<T> input); } // Strategy 1 class MergeSorter<T> : SortStrategy<T> where T : IComparable<T> { public event Action<IEnumerable<T>> UpdateUI; List<T> aux; int opCount = 0; public void Sort(IEnumerable<T> input) { UpdateUI(input); opCount++; List<T> sorteditems = new List<T>(input); aux = new List<T>(sorteditems.Count); for (int i = 0; i < sorteditems.Count; i++) aux.Add(default(T)); MergeSort(ref sorteditems, 0, sorteditems.Count - 1); UpdateUI(sorteditems); } private void Merge(ref List<T> a, int l, int m, int r) { // omitted private void MergeSort(ref List<T> a, int l, int r) { // omitted } // Strategy 2 class QuickSorter<T> : SortStrategy<T> where T : IComparable<T> { public event Action<IEnumerable<T>> UpdateUI; int opCount = 0; public void Sort(IEnumerable<T> input) { UpdateUI(input); opCount++; List<T> sorteditems = new List<T>(input); QuickSort(ref sorteditems, 0, sorteditems.Count - 1); UpdateUI(sorteditems); } private int Partition(ref List<T> a, int l, int r) { // omitted private void QuickSort(ref List<T> a, int l, int r) { // omitted } static class Program {
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7: Behavioral Patterns: Strategy, State, and Template Method
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145 146 147 148 149 150 151 static void Main( ) { Application.EnableVisualStyles( ); Application.SetCompatibleTextRenderingDefault(false); Application.Run(new StrategyView<int>(StartSetGenerator.GetStartSet)); } } }
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UpdateUI is an event that is set in line 84 (in the Context) to refer to DrawGraph. This is a more transparent way of the Strategy getting back to the animator than having it call DrawGraph directly. Notice that DrawGraph (lines 31 58) has an interesting loop
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that uses a new feature in C# 2.0: nullable types.
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Nullable types add to primitive types and structs the ability to include an undefined value. In keeping with objects, the value is called null, and it can be assigned and checked for. In programs, all primitive types are assigned default values on instantiation. Therefore, the ability to assign null to numeric and Boolean types is particularly useful when dealing with databases and other data types containing elements that may not be assigned a value. For example, a Boolean field in a database can store the values true or false, or it may be undefined. In C#, a nullable type is declared with the addition of a question mark (e.g., int x). An extra property HasValue can then be used to check whether a value is non-null. To convert back to a non-nullable type, use the as operator. as will return null if it cannot convert the value. For example, int val = DateTime.Now as int ; cf. C# Language Specification Version 3.0, September 2007, Section 4.1.10
Consider the loop in question. The items in the list are of type T, and it is possible that they might not have values. The cast to int on line 47 will therefore be trapped unless null is included as a possibility for val. In the next line, we can convert any possible nulls to zeros. Then, on line 51, we see that we have to convert the int type to int so that it can be used in arithmetic:
44 45 46 47 48 49 50 51 52 53 foreach (T item in list) { // val must be an integer. The as conversion needs it // also to be a non-nullable, which is checked by the int val = item as int ; if (!val.HasValue) val = 0; // Drawing methods do not handle nullable types b.SetPixel(x + 20, 20 + 200 - ((int)val), Color.Black); x++; }
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