How to freeze my app to wait for respond? - ios

Question

I have a simple app which try to login users.
User insert username and password
I call a method in another class ->
if ([myBankLogger checkUserLogin:self.memberNumber.text :self.accessCode.text])
{
//Check if user credential is correct
NSLog(#"Corrct");
}
else
{
NSLog(#"Not correct");
}
In checkUserLogin I send a http request to server and it takes a minute to get respond:
-(bool) checkUserLogin :(NSString*)username :(NSString*)password
{
__block bool tmp= false;
AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
[manager POST:string parameters:parameters progress:nil success:^(NSURLSessionTask *task, id responseObject) {
NSLog(#"JSON: %#", responseObject);
if (responseObject[#"secret_token"])
{
NSLog(#"HERE");
tmp = true;
}
} failure:^(NSURLSessionTask *operation, NSError *error) {
NSLog(#"Error: %#", error);
tmp = false;
}];
return tmp;
}
As it is normal compiler dose not wait until it finish processing. It returns false. I researched and found out I must use this:
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0ul);
dispatch_async(queue, ^{
// Perform async operation
// Call your method/function here
// Example:
// NSString *result = [anObject calculateSomething];
dispatch_sync(dispatch_get_main_queue(), ^{
// Update UI
// Example:
// self.myLabel.text = result;
});
});
But I am not sure where I should put my code? Appreciate any suggestion or easier solution.

Answer 1

If you perform a synchronous operation on the main thread, this will block the app UI for the entire duration of that sync operation. If it takes too much, the OS will kill the application execution. With an async approach using the dispatch method, you can solve the UI blocking problem:
[self.myRingLoading startAnimating]; // show a ring loading while the following long operation will take (here you are in the main thread scope)
// this dispatch block will move all the actions in an async thread, avoiding any UI blocking issue
dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){
// Perform here your UI blocking operation
// sample blocking ui operation
NSData* httpDataResult = [NSData dataWithContentsOfURL:#"http://api.yoursite.com/xyz"];
NSString* httpStringResult = [[NSString alloc] initWithData:httpDataResult encoding:NSUTF8StringEncoding];
// this dispatch block will send all action execution to the main queue, commonly the main thread
dispatch_async(dispatch_get_main_queue(), ^(void){
// Perform your UI operation (eg: printing the http response received by the server
[self.myUILabel setText:httpStringResult];
[self.myRingLoading stopAnimating]; // hide the ring loading since the long operation is finished
});
});
There are other native solutions for obtaining the result, for example using the NSOperation and NSOperationQueue. If you use AFNetworking, you can take advantage of several good implementations, for example AFHTTPRequestOperation:
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc]initWithRequest:request];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
// Perform your UI actions for the Success case
}
failure:^(AFHTTPRequestOperation *operation, NSError *error) {
// Perform your UI actions for the Failed case
}
];
// run the http operation process
[operation start];
Hope it helps