How do I initialize an instance variable when the object is created in Objective C?

In C++ I would do this in the constructor, but on Objective C开发者_如何学运维 I do not know how I am supposed to initialize it.

For example I have a member variable that has to be a dictionary and I want to initialize this dictionary.

When you say initialize the dictionary, I am assuming you just want to allocate memory for it. If so you can do the following sample:

- (id) init {
    self = [super init];
    if (self != nil) {
        _privateDict = [[NSMutableDictionary alloc] initWithCapacity:40];
    }
    return self;
}

Generally, you use the init method. For example:

Myclass *anInstance = [[MyClass alloc] init];

Some classes have specialized initializers that will take parameters. A classic example is any UIViewController subclass that you implement. Does this look familiar?

MyUIViewController *viewController = [[MyUIViewController alloc] initWithNibNamed: @"MyUIViewController" bundle: nil];

Notice the initWithNibNamed bit. You can write custom initializer like that as well. I suggest reading code that others wrote. Look for the initializer and try to understand how it was written/"set up".

To make a dictionary, you can use NSDictionary or NSMutableDictionary. Those have several initializers. You can use initWithObjects: and then pass in a bunch of objects to store in the dictionary.

You should read - The Objective-C Programming Language: Allocating and Initializing Objects