linq 實現動態 orderby

class Pet  
{  
   public string Name{get;set;}  
   public int Age{get;set;}  
}  
void Main()  
{   
      Pet[] pets = { new Pet { Name="Tim", Age=18 },  
                   new Pet { Name="Allen", Age=22 },  
                   new Pet { Name="Bill", Age=20  } };  
       
//如果我們想根據Age進行排序  很容易想到這樣來寫：      
  var query= from p in pets  
             orderby p.Age  
             select p;  
               
       
  query.ToList().ForEach(q=>Console.WriteLine(q.Name +"     "+q.Age));  
        /* 得到結果：  
        Tim     18 
        Bill    20 
        Allen   22 
        */  
          
}  
//但是有時項目內有多個排序條件 如有時要根據Name排序 有時要根據Age排序  何問起 hovertree.com
       //這時我們就要用到動態排序:  
void Main()  
{   
    Pet[] pets = { new Pet { Name="Tim", Age=18 },  
                   new Pet { Name="Allen", Age=22 },  
                   new Pet { Name="Bill", Age=20 } };  
    Console.WriteLine("Before Orderby:/r/n");         
    pets.ToList().ForEach(p=>Console.WriteLine(p.Name +"     "+p.Age));  
       
  var query= from p in pets  
             orderby GetPropertyValue(p,"Age")    
             select p;  
               
    Console.WriteLine("/r/nAfter Orderby:/r/n");  
  query.ToList().ForEach(q=>Console.WriteLine(q.Name +"     "+q.Age));  
           /* 
        Before Orderby: 
        Tim     18 
        Allen   22 
        Bill    20 
        After Orderby: 
         
        Tim     18 
        Bill    20 
        Allen   22 
        */         
}  /* 何問起 hovertree.com */
private static object GetPropertyValue(object obj, string property)  
{  
    System.Reflection.PropertyInfo propertyInfo=obj.GetType().GetProperty(property);  
    return propertyInfo.GetValue(obj, null);  
} 

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