返回值

Question

如何構建表達式樹在C＃中返回基於屬性的名稱的屬性的值

Func<Foo, long> getValue(string propertyName) 
{ 
    // i think that the beginning of the expression tree would look like this 
    // but i'm not sure this is correct 
    var inputParameter = Expression.Parameter(typeof(Foo)); 
    var desiredProperty = typeof(Foo).GetProperty(propertyName); 
    var valueOfProperty = Expression.Property(inputParameter, desiredProperty); 
    // ... ??? todo: expression that returns value 
} 

調用該函數看起來像這樣這部分傳遞到LINQ的選擇方法的另一種表達：

value = getValue("Bar").Invoke(FooInstance) 

Answer 1

應該是足夠了：

var lambda = Expression.Lambda<Func<Foo, long>>(valueOfProperty, inputParameter); 
return lambda.Compile(); 

無論如何 - 當你可以通過反射直接獲得價值時，構建Expression的目的是什麼？

return someFoo => (long)desiredProperty.GetValue(someFoo);