Expression.TryCatchFinally Method

Parameters

• body
  Type: System.Linq.Expressions.Expression
  The body of the try block.

• finally
  Type: System.Linq.Expressions.Expression
  The body of the finally block.

• handlers
  Type: array<System.Linq.Expressions.CatchBlock[]
  The array of zero or more CatchBlock expressions representing the catch statements to be associated with the try block.

Return Value

Type: System.Linq.Expressions.TryExpression
The created TryExpression.

        ' Add the following directive to the file:
        ' Imports System.Linq.Expressions 

        ' A TryExpression object that has a catch statement and a finally statement.
        ' The return types of the try block and all catch blocks must be the same.
        Dim tryCatchExpr As TryExpression =
            Expression.TryCatchFinally(
                Expression.Block(
                    Expression.Throw(Expression.Constant(New DivideByZeroException())),
                    Expression.Constant("Try block")
                 ),
            Expression.Call(
                GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}),
                Expression.Constant("Finally block")
            ),
            Expression.Catch(
                GetType(DivideByZeroException),
                Expression.Constant("Catch block")
            )
        )

        ' The following statement first creates an expression tree,
        ' then compiles it, and then runs it.
        ' If the exception is caught, 
        ' the result of the TryExpression is the last statement 
        ' of the corresponding catch statement.
        outputBlock.Text &= Expression.Lambda(Of Func(Of String))(tryCatchExpr).Compile()() & vbCrLf

        ' This code example produces the following output:
        '
        ' Finally block
        ' Catch block

// Add the following directive to the file.
// using System.Linq.Expressions;  

// A TryExpression object that has a catch statement and a finally statement.
// The return types of the try block and all catch blocks must be the same.
TryExpression tryCatchExpr =
    Expression.TryCatchFinally(
        Expression.Block(
            Expression.Throw(Expression.Constant(new DivideByZeroException())),
            Expression.Constant("Try block")
        ),
        Expression.Call(typeof(Console).GetMethod("WriteLine", new Type[] { typeof(string) }), Expression.Constant("Finally block")),
        Expression.Catch(
            typeof(DivideByZeroException),
            Expression.Constant("Catch block")
        )
    );

// The following statement first creates an expression tree,
// then compiles it, and then runs it.
// If the exception is caught, 
// the result of the TryExpression is the last statement 
// of the corresponding catch statement.
outputBlock.Text += Expression.Lambda<Func<string>>(tryCatchExpr).Compile()() + "\n";

// This code example produces the following output:
//
// Finally block
// Catch block