• Article

TryExpression Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Represents a try/catch/finally/fault block.

Inheritance Hierarchy

System.Object
  System.Linq.Expressions.Expression
    System.Linq.Expressions.TryExpression

Namespace:  System.Linq.Expressions
Assembly:  System.Core (in System.Core.dll)

Syntax

'Declaration
Public NotInheritable Class TryExpression _
    Inherits Expression

public sealed class TryExpression : Expression

The TryExpression type exposes the following members.

Properties

  Name Description
Public property Body Gets the Expression representing the body of the try block.
Public property CanReduce Indicates that the node can be reduced to a simpler node. If this returns true, Reduce() can be called to produce the reduced form. (Inherited from Expression.)
Public property Fault Gets the Expression representing the fault block.
Public property Finally Gets the Expression representing the finally block.
Public property Handlers Gets the collection of CatchBlock expressions associated with the try block.
Public property NodeType Returns the node type of this Expression. (Overrides Expression.NodeType.)
Public property Type Gets the static type of the expression that this Expression represents. (Overrides Expression.Type.)

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Methods

  Name Description
Protected method Accept Dispatches to the specific visit method for this node type. For example, MethodCallExpression calls the VisitMethodCall. (Inherited from Expression.)
Public method Equals(Object) Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected method Finalize Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
Public method GetHashCode Serves as a hash function for a particular type. (Inherited from Object.)
Public method GetType Gets the Type of the current instance. (Inherited from Object.)
Protected method MemberwiseClone Creates a shallow copy of the current Object. (Inherited from Object.)
Public method Reduce Reduces this node to a simpler expression. If CanReduce returns true, this should return a valid expression. This method can return another node which itself must be reduced. (Inherited from Expression.)
Public method ReduceAndCheck Reduces this node to a simpler expression. If CanReduce returns true, this should return a valid expression. This method can return another node which itself must be reduced. (Inherited from Expression.)
Public method ReduceExtensions Reduces the expression to a known node type (that is not an Extension node) or just returns the expression if it is already a known type. (Inherited from Expression.)
Public method ToString Returns a textual representation of the Expression. (Inherited from Expression.)
Public method Update Creates a new expression that is like this one, but using the supplied children. If all of the children are the same, it will return this expression.
Protected method VisitChildren Reduces the node and then calls the visitor delegate on the reduced expression. The method throws an exception if the node is not reducible. (Inherited from Expression.)

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Remarks

The body block is protected by the try block.

The handlers consist of a set of CatchBlock expressions that can be either catch statements or filters.

The fault block runs if an exception is thrown.

The finally block runs regardless of how control exits the body.

Only one of fault or finally blocks can be supplied.

The return type of the try block must match the return type of any associated catch statements.

Examples

The following example demonstrates how to create a TryExpression object that contains a catch statement by using the TryCatch method.

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

' A TryExpression object that has a Catch statement.
' The return types of the Try block and all Catch blocks must be the same.
Dim tryCatchExpr As TryExpression =
       Expression.TryCatch(
           Expression.Block(
               Expression.Throw(Expression.Constant(New DivideByZeroException())),
               Expression.Constant("Try 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:
'
' Catch block

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

// A TryExpression object that has a Catch statement.
// The return types of the Try block and all Catch blocks must be the same.
TryExpression tryCatchExpr =
    Expression.TryCatch(
        Expression.Block(
            Expression.Throw(Expression.Constant(new DivideByZeroException())),
            Expression.Constant("Try 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:
//
// Catch block

Version Information

Silverlight

Supported in: 5, 4

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.