Expression Tree Tutorial TryCatchFinally

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));
}

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