目标C整数第一次是0，但是第二次改变

Question

Okay so i have this program that is suposed to communicate over a Webserver(PHP Script)

I have this method that i want to get a random id for a table. The return data of this NSURLconnection is supose to be the amount of rows in the table.

First time i call it, its like randomid variables does not get set, but second time i run it, it does get set.

variable setting:

@implementation ViewController {
NSMutableData *randomData;
int randomid;
}

Here is my IBaction for a button:

- (IBAction)initVits:(id)sender {
[self randomID];
NSLog(@"Random ID: %d", randomid);    
}

The output first time is: Random ID: 0, second time: Random ID: a valid id

RandomID:

- (void) randomID {

NSString *url = @"http://ivitserdk.porkhost.dk/ivitserdk.php?function=randomid";
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:url]   cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:1.0];
connectionRandomID = [[NSURLConnection alloc] initWithRequest:request delegate:self];

randomData = [NSMutableData data];
[connectionRandomID start];
}

Connection did finish loading:

 if(connection == connectionRandomID) {
    NSString *String = [[NSString alloc] initWithData:randomData encoding:NSUTF8StringEncoding];
    NSLog(@"Return: %@", String);
    int temp = [String integerValue];
    NSLog(@"temp: %d", temp);
    randomid = (arc4random() % temp) + 1;
    NSLog(@"Random: %d", randomid);
    randomData = nil;
    connectionRandomID = nil;
 }

Output is for all times: Return: (number of rows in table) temp: (number of rows in table to a int) Random: (a random number)

Its like the randomid variable does not get set the first time.

Thanks for your time!

Answer 1

[self randomID] returns immediatly because you are doing an async call inside randomID function.

randomid is set on the didFinish callback that it is executed after you NSLog the ivar randomid.

Answer 2

You are using asynchronous networking, so your NSLog is called before the random ID is retrieved from the server. There are multiple solutions to this.

• Use synchronous networking (I don't recommend this, so I don't go further into that)
• Put the NSLog statement or whatever you want to do when the ID is generated at the end of your connectionDidFinishLoading method
• If possible, I'd recommend generating the ID on the device (but I guess you need an unique key for a database, an URL or something, so this will probably not work for you)

Answer 3

Did you add this ?

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
// Append the new data to receivedData.
// receivedData is an instance variable declared elsewhere.
[randomData appendData:data];
}