The Expression.IfThenElse method creates a ConditionalExpression that represents a conditional block with if and else statements. For example, you have the following code.
int num = 60;
if(num > 10)
{
Console.WriteLine("num is greater than 10");
}
else
{
Console.WriteLine("num is less than or equan to 10");
}
Here is the code that is required to build the same functionality using expression tree.
int num = 60;
var testCondition = Expression.Constant(num > 10);
var ifTrueBlock = WriteLineExpression("num is greater than 10");
var ifFalseBlock = WriteLineExpression("num is less than or equal to 10");
var ifThenElseExpr = Expression.IfThenElse(
testCondition,
ifTrueBlock,
ifFalseBlock);
Expression.Lambda<Action>(ifThenElseExpr).Compile()();
This example shows how to create an expression that represents an if-else block. Here is the code for WriteLineExpression method
public static Expression WriteLineExpression(string s)
{
return Expression.Call(null,
typeof(Console).GetMethod("WriteLine", new Type[] { typeof(String) }),
Expression.Constant(s));
}