New to Telerik UI for WPF? Download free 30-day trial

Expression Parser

In some scenarios, you do not need the graphical user interface of the RadExpressionEditor, but would rather just require its parsing logic for a given expression.

As of R3 2021, you can use the new RadExpressionParser class to achieve this requirement.

It exposes the following methods which you can use to parse your expressions:

  • LambdaExpression Parse(string expression)
  • Task ParseAsync(string expression)
  • Task ParseAsync(string expression, CancellationToken cancellationToken)
  • bool TryParse(string expression, out LambdaExpression lambda)

Check out the ExpressionParser online demo to see the RadExpressionParser in action.

Parse

You can use the Parse method to try to directly parse the expression and return a LambdaExpression if successfully parsed. Please note, however, that an ExpressionParserException will be thrown if the expression cannot be parsed.

Example 1: Using the Parse method

try 
{ 
    var lambdaExpression = expressionParser.Parse(expression); 
    var result = lambdaExpression.Compile().DynamicInvoke().ToString(); 
} 
catch (ExpressionParserException ex) 
{ 
    var errorMessages = string.Join("\n", ex.Errors.Select(er => er.Message)); 
} 

ParseAsync

The two overloads of the ParseAsync method operate in the same manner as the Parse method, with the difference being that they are performed asynchronously. In the second overload, aside from the expression to be parsed, you can pass a cancellation token that will be assigned to the new task.

TryParse

The TryParse method tries to convert the string representation of an expression to its LambdaExpression equivalent. The returned value indicates whether the conversion succeeded or failed. The out parameter will contain null if the parsing was unsuccessful.

Example 2: Using the TryParse method

LambdaExpression lambdaExpression; 
var isExpressionValid = expressionParser.TryParse(expression, out lambdaExpression); 
if (isExpressionValid) 
{ 
    var result = lambdaExpression.Compile().DynamicInvoke().ToString(); 
} 
else 
{ 
    // display an error message 
} 

Item

You can use the Item property to be able to access the public members of the passed object.

Example 3: Setting the Item property

this.expressionParser.Item = this.ProductsGridView.SelectedItem; 
Note that when using the generated expression, you would then need to pass the same item as the parameter as shown in Example 4.

Example 4: Passing the Item as a parameter of the expression

var lambdaExpression = this.expressionParser.Parse(expression); 
string result; 
if (lambdaExpression.Parameters.Count == 1) 
{ 
    result = lambdaExpression.Compile().DynamicInvoke(this.expressionParser.Item).ToString(); 
} 
else 
{ 
    result = lambdaExpression.Compile().DynamicInvoke().ToString(); 
} 

See also

In this article
Not finding the help you need? Improve this article