C# InvalidCastException

Understand InvalidCastException, which occurs when a cast fails.

InvalidCastException. An InvalidCastException has been thrown. The InvalidCastException occurs when an explicit cast is applied. But the type is not in the same path of the type hierarchy. The cast does not succeed.Casts Exception

Example. First, this program shows an InvalidCastException being thrown by the .NET Framework. An InvalidCastException is generated by the runtime when a statement tries to cast one reference type to a reference type that is not compatible.

Info: Casts that use the type name in parentheses are called explicit casts. Usually this exception indicates a coding error.

Tip: It is possible to remedy this by defining a custom explicit cast method, but not usually recommended.

Instead: Avoiding casting (by using generics or objects) is usually the best. This may help performance and code readability.

C# program that generates InvalidCastException using System.IO; using System.Text; class Program { static void Main() { // Creates a new object instance of type StringBuilder. // ... Then uses implicit cast to object through assignment. // ... Then tries to use explicit cast to StreamReader, but fails. StringBuilder reference1 = new StringBuilder(); object reference2 = reference1; StreamReader reference3 = (StreamReader)reference2; } } Output Unhandled Exception: System.InvalidCastException: Unable to cast object of type 'System.Text.StringBuilder' to type 'System.IO.StreamReader'. at Program.Main() in ...Program.cs:line 13

Notes, example steps. The first reference happens to be of type StringBuilder. This exact type is not important. Then an object type is assigned to the StringBuilder reference, providing an implicit conversion to object type.StringBuilder

Next: A reference of type StreamReader is explicitly cast to the object reference.

And: This causes the runtime to throw an exception of type System.InvalidCastException. The 2 types are not compatible.

StreamReader

Generics. In the first few versions of the .NET Framework, generic types did not exist and you had to frequently cast from the ArrayList and Hashtable types. This caused a performance hit because of the boxing and unboxing conversions.ArrayList Hashtable

However: Current versions provide the List and Dictionary types, which do not require casting, thus avoiding the problem.

List Dictionary

Operators. The C# language also defines the "is" and "as" operators, and these operators can be used to perform safe casts. If one of these casts fails, you will not get an exception. Instead you will receive the value false or null.Is As

Summary. We looked at the InvalidCastException type and demonstrated its cause in a C# program. This exception is raised when you try to cast an object reference to a more derived class that is not compatible because of a different type hierarchy.

The Dev Codes

.Net

.NET Array Dictionary List String 2D Async DataTable Dates DateTime Enum File For Foreach Format IEnumerable If IndexOf Lambda LINQ Parse Path Process Property Regex Replace Sort Split Static StringBuilder Substring Switch Tuple

Java

Core Array ArrayList HashMap String 2D Cast Character Console Deque Duplicates File For Format HashSet If IndexOf Lambda Math ParseInt Process Random Regex Replace Sort Split StringBuilder Substring Switch Vector While

TheDeveloperBlog.com

C# InvalidCastException

Related Links:

.Net

Java

Related Links