You can build an expression tree which contains a try-catch and finally blocks by using Expression.TryCatchFinally method. It creates a TryExpression representing a try block with any number of catch statements and a finally block.
For example, you have the following code.
try
{
Console.WriteLine("Try block");
throw new DivideByZeroException();
Console.WriteLine("After throwing exception");
}
catch (DivideByZeroException)
{
Console.WriteLine("Catch block");
}
finally
{
Console.WriteLine("Finally block");
}
Here is the code that is required to build the same functionality using expression tree.
var tryBlock = Expression.Block(
WriteLineExpression("Try block"),
Expression.Throw(Expression.Constant(new DivideByZeroException())),
WriteLineExpression("After throwing exception")
);
var catchBlock = Expression.Catch(
typeof(DivideByZeroException),
WriteLineExpression("Catch block")
);
var finallyBlock = WriteLineExpression("Finally block");
TryExpression tryFinallyExpr = Expression.TryCatchFinally(tryBlock, finallyBlock, catchBlock);
Expression.Lambda<Action>(tryFinallyExpr).Compile()();
This example shows how to create an expression that contains a goto statement. 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));
}