iOS Development > Data Modeling > Using A Custom Class Quiz

so is declaring a variable from a class the same thing as calling a variable name that you created..?

like NSString *myString = @"treehouse";

would creating an instance be declaring the variable name "myString" somewhere later in my code?

That's right myString is an instance of NSString. The statement above is the same as saying NSString *myString = [[NSString alloc] initWithString:@treehouse"]; except that the compiler knows that anything prefixed with an at symbol (@) is a literal which means it's a shorthand way of declaring an instance. We are working on an Objective-C course but meanwhile you might benefit from a getting a book on Objective-C.

i have a book and a few great resources already. Im really just trying to juggle college and treehouse. On the other hand, i think something that would help a lot of us would be completing more simple projects on our own. BUT using the information that you guys just taught us in that specific learning adventure.

Alot of us find it hard to retain alot of the information.

I believe it would help if you guys show us that after you teach us one thing, those same methods and techniques that you just taught can apply to other projects. Then leave it up to us to stretch our creativity and completing the projects.

just a suggestion though.

if I'm asked to create an instance of UIImage called 'image' given the name of the image is 'placeholder.png'.

would this be correct? if not, could you tell me which side of my equation needs work?

UITableViewCell *cell = [[UITableViewCell alloc] init];
/* Write your code below this line */
cell.imageView.image = [UIImage imageNamed:@"placeholder.png"];

Your answer is right! You got it.

EDIT: If the question is "Create an instance of UIImage called 'image' given the name of the image is 'placeholder.png'."

Then on the left you need to create an object called image:

UIImage *image = [UIImage imageNamed:@"placeholder.png"];

thank you,

now let me ask you this, Do instances always have to be implied by an '-' before your line of code?

another question i have about instances is in what cases do you have to call an instance versus using a method.

or am i confused about them both and that an instance usually consists of methods.

basically my second question is.. Is an instance a series of methods followed by a "-" sign?

Answers to your questions:

Q: Do instances always have to be implied by an '-' before your line of code? No instance methods start with a '-' and not an instance variable.

Let's take the class UIView as an example. To create an instance of UIView called myView you would do the following:

UIView *myView = [[UIView alloc] init];

In the above example the variable myView is an instance of the class UIView. Think of the the class as a template that defines the properties and methods. Now you create your occurance (instance) of a view using this template (class) called UIView.

Q: In what cases do you have to call an instance versus using a method.

A method is something you call upon an instance. So taking the above examples of myView. Now that you have an instance of UIView you can call an instance method:

          Method
              |
[myView sizeToFit];
    |
Instance

Rashii and Amit,

Thanks for posting this discussion. I'm struggling with the same quiz and can't seem to figure out where I've lost the track.

I've watched the Using a Custom Class video more times than I can count. I think I need some reading material. Do either of you have any recommendations?

I found an interesting section in the Objective-C documentation called Defining Classes. Going to start there. Any other suggestions would be great!

Best,

Mike

One suggestion would be to look forward to the Objective-C lessons that come out sometime this month.

Another would be to look for some Objective-C primers. I don't have the links to any of the threads anymore but they're somewhere in these forums. i'll go look for them and send you the links.

Mike Mitchell check out this discussion: https://teamtreehouse.com/forum/objective-c