Every once in awhile, you come across this exception: System.Null Reference Exception – “Object reference not set to an instance of an object.” You see people asking about this everywhere; about why are they getting this error. Note, regardless of the scenario, the cause is always the same in .To work with complex or user-defined parameter types, you can use the property.In your business object, creating methods with long parameter lists that map control values one-to-one to data store values can result in code that is not easily reusable.
it does not update database, just marks rows in datatable that shows they are changed and ready to be reflected to db...Empty, or to some other actual value, before it will compile in C#, or run without exception in VB. Net, set [a = “something”] before you attempt to do anything with it. Strings and some other CTS types have a misconception of being value types, like Integers, and they are not.A more complex example would be that you disposed of a class that maybe you use to access the database. But then, somewhere else, you tried to call a method of that class that used those objects that no longer exists.This is most common in classes where you are using class-wide instantiated objects.If you create and drop your objects within each method, this isn’t going to be a problem, and you are actually following a better guideline by creating at the last necessary moment, and destroying at the first possible moment, not to mention avoiding possible exceptions like Invalid Reference Exception.A better practice is to encapsulate your data in a custom class and then pass an instance of the class as a parameter.That way, the data that makes up an instance of the class, such as an employee record, can change without requiring any changes to the public interfaces exposed by the data source object.Again, same exception gets thrown, but coming from withing the instantiated class itself.The Get Orders function inside of Customers requires an instance of a connection, but you disposed of the required objects required to access the database back up in Load Data() when you called a. Be careful when you clean up your instances, that you are not using them again somewhere.Net: You are trying to use a reference variable who’s value is Nothing/null.When the value is Nothing/null for the reference variable, that means it is not actually holding a reference to an instance of any object that exists on the heap. Net, you are trying to access a string that has not been initialized. You can’t even compile code like the following in C# Remember, a string is a reference type (a character array) that has to have a value.