Question

I saw some code like this :

NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:urlRequest delegate:self];

if(connection) {
    receivedData = [NSMutableData data];
} else {

}

How do I make it to go into the else? I tried disabling the connection and still never go into the else it goes through the didFailWithError … so wondering if it is even necessary??

Answer 1

The apple documentation on the return value of this method says:

Return Value

The URL connection for the URL request. Returns nil if a
connection can’t be initialized.

This could be misleading for those not familiar with Cocoa (and Objective-C) best practices.

Generally an init method should return an object; unless there is some fundamental reason returning an object would be dangerous. Most other languages handle cases like this by throwing exceptions, requiring you to add countless try/catch brackets.

The initWithRequest:delegate: method will return nil if (for example) you pass a nil as the request parameter; and for good reason. Why create a connection object to have no useful purpose?

However lets consider a situation like airplane mode or an invalid url. If initWithRequest:delegate: just returned nil then how would you know what went wrong? Allowing the connection to call connection:didFailWithError: gives you an opportunity to gain insight into the particular failing, through the error parameter.

To address your question as to whether handling the event of the connection being nil is ever necessary: It depends. If the connection fails to initialize it will never call the connection delegate methods, so if your code relies on these callbacks to issue subsequent requests then yes it’s necessary.

A side note: Creating your NSMutableData here is a little premature since you don’t yet know that there is a valid connection. An answer I gave here gave some very basic sample code regarding where to do this.