iOS：为什么我在Xcode中得到“未使用的变量”？

Question

I'm coding to display a php echo

NSMutableURLRequest *request = [[NSMutableURLRequest alloc]init];
[request setTimeoutInterval:180.0]; 
[request setURL:[NSURL URLWithString:@"http://localhost:8888/MAMP/signup/getkey.php"]]; 
[request setHTTPMethod:@"POST"];

NSString *key = [[NSString alloc] initWithData:[NSURLConnection    sendSynchronousRequest:request returningResponse:nil error:nil] encoding:NSUTF8StringEncoding];

When I compile, I have this warning message : Unused variable key

Where is the problem?

Answer 1

It is because you don't do anything with key . You simply alloc and init it, but never really use it.

You could do something like NSLog(@"%@",key); and the error will go away.

The other option is to set Unused Variables to warnings. Go to your project target, Build settings, then find the below image and change Unused Variables to Yes . This will change it from and error to a warning.

Answer 2

On the last line you are assigning key to a value but you never use it. You can configure it to not throw an error, but rather a warning if you do not use a variable. Otherwise just comment out the assignment of key.

Answer 3

如果您不需要使用该键，只需用//将其注释掉

// NSString *key = [[NSString alloc] initWithData:[NSURLConnection    sendSynchronousRequest:request returningResponse:nil error:nil] encoding:NSUTF8StringEncoding];