NSString响应 rangeOfString:，而不是 rangeWithString:.

NSString responds to rangeOfString:, not rangeWithString:.

在 if 语句和 else 语句中都声明了变量urlAddress.这意味着它仅存在于该范围内.离开if/else语句后，变量就消失了.

The variable urlAddress is declared both in the if statement, and in the else statement. That means it only lives in that scope. Once you leave the if/else statement, the variable is gone.

对于URL，***以方案开头(例如"http://")，并且您的代码将很高兴接受apple.http://.com为有效.

For a URL it's best if it begins with the scheme (like "http://"), and your code will gladly accept apple.http://.com as being valid.

您可以改为使用 hasPrefix:方法，如下所示:

You can use the hasPrefix: method instead, like this:

BOOL result = [[check lowercaseString] hasPrefix:@"http://"];
NSURL *urlAddress = nil;

if (result) {  
    urlAddress = [NSURL URLWithString: textField.text];
}
else {
    NSString *good = [NSString stringWithFormat:@"http://%@", [textField text]];
    urlAddress = [NSURL URLWithString: good];
}

NSURLRequest *requestObject = [NSURLRequest requestWithURL:urlAddress];