Guard Class

Represents an argument checker. Exposes members used to validate method parameters.

Namespace: DevExpress.ExpressApp.Utils

Assembly: DevExpress.ExpressApp.v24.2.dll

NuGet Package: DevExpress.ExpressApp

Declaration

C#

public static class Guard

VB.NET

Public Module Guard

Remarks

The main purpose of the Guard class is to validate parameters passed into a method. The class “guards” methods from passing invalid parameters into them. Methods exposed by the Guard class are designed to throw exceptions if a parameter being checked does not pass validation.

Consider the following sample method:

C#

public void MyMethod(object myObject, string message) {
    if(myObject == null) {
        throw new ArgumentNullException();
    }
    if(myObject.GetType() != typeof(MyType)) {
        throw new ArgumentException();
    }
    else {                
        //...custom logic here
        if(!string.IsNullOrEmpty(message)) {
            //...custom logic here
        }                
    }                
}

VB.NET

Public Sub MyMethod(ByVal myObject As Object, ByVal message As String)
    If myObject Is Nothing Then
            Throw New ArgumentNullException()
    End If
    If myObject.GetType() IsNot GetType(MyType) Then
        Throw New ArgumentException()
    Else
        '...custom logic here
        If (Not String.IsNullOrEmpty(message)) Then
            '...custom logic here
        End If
    End If
End Sub

Having argument checks throughout the body of the method clutters the code and makes it less readable. Moreover, checking arguments in such a manner is not a good way of declaring business logic. The following code snippet illustrates the same method rewritten using the Guard class:

C#

public void MyMethod(object myObject, string message) {
    Guard.ArgumentNotNull(myObject, nameof(myObject));
    Guard.ArgumentNotNull(message, nameof(message));
    Guard.TypeArgumentIs(typeof(MyType), myObject.GetType(), nameof(myObject));
    //...custom logic here                
}

VB.NET

Public Sub MyMethod(ByVal myObject As Object, ByVal message As String)
    Guard.ArgumentNotNull(myObject, NameOf(myObject))
    Guard.ArgumentNotNull(message, NameOf(message))
    Guard.TypeArgumentIs(GetType(MyType), myObject.GetType(), NameOf(myObject))
    '...custom logic here                
End Sub

As you can see, after the rewrite, the code became shorter and more readable. Also, by using the Guard class in such a manner we express and enforce a data contract. Combined with self-describing names of the Guard class’ methods, this makes the sample code rather self-documenting.

The following table lists the methods exposed by the Guard class:

Method	Description
Guard.ArgumentNotNull	Ensures that a specific argument is not a null reference.
Guard.ArgumentNotNullOrEmpty	Ensures that a specific string argument is not a null reference and is not an empty string.
Guard.CheckObjectFromObjectSpace	Ensures that a specific object belongs to a particular Object Space.
Guard.CreateArgumentOutOfRangeException	Initializes a new ArgumentOutOfRangeException class with the specified argument name and value.
Guard.NotDisposed	Ensures that a specific object has not been disposed.
Guard.TypeArgumentIs	Ensures that an argument has a specific type.

Inheritance

Object

Guard