27
décembre
2012
[.NET] Linq et type dynamique, attention au piège
décembre
2012
Un article de aymeric.lagier
Problème
Le code suivant affiche « Numbers greater than 3 are : 6 7 » au lieu du « Numbers greater than 3 are : 4 5 6 7 » attendu.
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class Program { static void Main(string[] args) { List<Int32> allNumbers = new List<Int32>() { 1, 2, 3, 4, 5, 6, 7 }; List<dynamic> greaterNumbers = new List<dynamic>(); // Finding all numbers from the "allNumbers" list that are greater // than "currentNumber" for (Int32 currentNumber = 0; currentNumber < 5; currentNumber++) { dynamic item = new ExpandoObject(); item.Number = currentNumber; item.GreaterNumbers = allNumbers.Where(e => e > currentNumber); greaterNumbers.Add(item); } // Here greaterNumbers contains 5 items // We want to display numbers greater than 3 dynamic greaterThan3 = greaterNumbers .FirstOrDefault(i => i.Number == 3); if (greaterThan3 != null) { Console.Write("Numbers greater than 3 are : "); foreach (Int32 greaterNumber in greaterThan3.GreaterNumbers) { Console.Write(greaterNumber); Console.Write(' '); } Console.WriteLine(); } } }