Vb.net – Casting in VB.NET

castingctypevb.net

I would like to be able to cast a value dynamically where the type is known only at runtime. Something like this:

myvalue = CType(value, "String, Integer or Boolean")

The string that contains the type value is passed as an argument and is also read from a database, and the value is stored as string in the database.

Is this possible?

Best Solution

 Dim bMyValue As Boolean
 Dim iMyValue As Integer
 Dim sMyValue As String 
 Dim t As Type = myValue.GetType


 Select Case t.Name
     Case "String"
        sMyValue = ctype(myValue, string)
     Case "Boolean"
        bMyValue = ctype(myValue, boolean)
     Case "Integer"
        iMyValue = ctype(myValue, Integer)
 End Select

It's a bit hacky but it works.

Related Solutions

C# – Direct casting vs ‘as’ operator

string s = (string)o; // 1

Throws InvalidCastException if o is not a string. Otherwise, assigns o to s, even if o is null.

string s = o as string; // 2

Assigns null to s if o is not a string or if o is null. For this reason, you cannot use it with value types (the operator could never return null in that case). Otherwise, assigns o to s.

string s = o.ToString(); // 3

Causes a NullReferenceException if o is null. Assigns whatever o.ToString() returns to s, no matter what type o is.

Use 1 for most conversions - it's simple and straightforward. I tend to almost never use 2 since if something is not the right type, I usually expect an exception to occur. I have only seen a need for this return-null type of functionality with badly designed libraries which use error codes (e.g. return null = error, instead of using exceptions).

3 is not a cast and is just a method invocation. Use it for when you need the string representation of a non-string object.

Objective-c – In Objective-C, what is the equivalent of Java’s “instanceof” keyword

Try [myObject class] for returning the class of an object.

You can make exact comparisons with:

if ([myObject class] == [MyClass class])

but not by using directly MyClass identifier.

Similarily, you can find if the object is of a subclass of your class with:

if ([myObject isKindOfClass:[AnObject class]])

as suggested by Jon Skeet and zoul.

Best Solution

Related Solutions

C# – Direct casting vs ‘as’ operator

Objective-c – In Objective-C, what is the equivalent of Java’s “instanceof” keyword

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