Two simple? questions

Question

First question:

I have a class in a separate file. Then I have a form with some controls.

How can I get access to the controlls in my class? Tried Form1.richTextBox1 but that doesn´t work.

Second question:

I am creating object dynamicly.

In a form I use textBoxes to create values for the constructor.

Then in a button event I create an object and add it to a List, something like this.

car jaguar = new car(textBox1.Text, textBox2.Text);

carList.Add(car);

I know this works but how?

Everytime a new object is created it gets the same name. Does it work because you put it in the list and is it then impossible to find it in the list using the name of the object?

Sam Hobbs · Answer

First note that it works much better if you ask just one question in a thread. There are many reasons for this. One is that it helps to give threads more meaningful subjects than Two simple? questions. Another is that it helps others in the future looking for answers. Note that this web site requests that you mark a reply as the answer and if there are multiple questions and multiple replies with answers then you cannot mark one of the many as an answer. Also it helps people trying to help you if each thread is asking just one question. Sometimes questions are related and it is appropriate to consider them one question and in that case they are one question. As Vulpes indicates there are many ways to access controls in a form. Vulpes's suggestion is easy to explain. If this thread was about just that question and if you had provided more information then we could suggest something more relevant. The easy soluton that Vulpes shows is not object-oriented. I do not understand how the source code works that you say works. You have  car jaguar =  and then car is added. However car is the type; the class or struct. Are you sure that works? It would help to know what experience you have. If you have experience with another language then it will help to compare C# to the other language. In most other languages a variable is equivalent to the data it contains. C# is different in that for objects of a class the variable is a reference. This concept is confusing for us when we are familiar with other languages. In C# when a reference type is asssigned it is usuallly only the reference (32-bits or 64-bits) that is copied around. The variable only represents the reference. So when you add the object to a list or array just the reference is used. There is just one instance of the data and the variables only contain references to the data.

Lars Persson · Answer

Ok i see. Again thanks!

Sam Hobbs · Answer

Let's discuss what happens in C++. In C++ if a local variable is allocated on the stack then the variable will go out of scope when the function exits and the item will be automatically deleted. If however the same object were allocated in the heap using the new keyword then the pointer to the object would be on the stack. When the function exits the pointer would be unavailable but the object it points to would still be in the heap. If the pointer were to be put into a collection of some type that existed before the function is called then the collection's copy of the pointer would still exist after the function exits and the object would remain in the heap. As Vulpes said a reference is like a pointer. In C# classes are reference types and are very much like pointers. A C# reference is different from a pointer in that a reference actually includes data used by the garbage collector. In C# a new reference type is created by each use of the new keyword. A reference type can be copied to someplace such as into a collection. If no more uses of a reference type exist then the garbage collector assumes it is not needed and then the object is destroyed. In C++ there is a one-for-one correspondence of items in the heap and execution of the new keyword and the equivalent applies to C# reference types. In C++ there must be one delete keyword used for every new keyword but in C# objects are automatically destroyed when there are no more references to an object. Putting an object in a collection creates (copies) a reference thereby preserving the object from garbage collection even if the original variable for the object goes out of scope.

Lars Persson · Answer

Well Sam first of all thanks for the reply and the thanks for the advice. In the future I will only post one question in a thread. As for the lines: car jaguar = new car(textBox1.Text textBox2.Text); carList.Add(car); it was only an example and you are right. I wouldn't work. Of course it should be jaguar that I add and not car. I have experience with a lot of languages like Java C/C++/C#/Objective-C but not a full understanding of any of the languages I would say. I understand the concept of reference-type and pointers altough it can be confusing sometimes. So if I understand it correctly it is like this: If you create three objects in say a console-project the have to have different names otherwise the interpreter would be confused. If you put the code I wrote in an event for a button everytime a new object is created with the same name. That doesn´t matter thought because the interpreter can still keep track of every object. However it is not possible to access an object by name?

Lars Persson · Answer

Great thanks!

Vulpes · Answer

To access a control on a form you first have to get a reference to the form instance itself. There are many ways to do this. The way I'll show you here doesn't require any changes to existing code though it's not necessarily the best or easiest way. Suppose the Form class is called Form1 and richTextBox1 is placed directly on it and not in some container such as a Panel or GroupBox. Then you can access the RTB as follows: using System.Windows.Forms; // make sure this line is in your class file // ... Form f1 = (Form1)Application.OpenForms[Form1]; RichTextBox rtb = (RichTextBox)f1.Controls[richTextBox1]; rtb.Text = Something different!; Even though an object may have exactly the same property values as another object the fact remains that they are separate objects. The jaguar variable will hold a reference (i.e. a pointer) to where the object assigned to it is stored on the heap. Similarly carList which is a List will hold internally an array of references to the car objects which have been added to it and can therefore distinguish these objects by their references. The programmer can still distinguish between objects with the same property values by their index within the List.