iOS Synchrounous calling asynchronous methods - ios

Question

I am calling checkWeathermethod then I will store into the database by calling storeWeatherIntoDB. After storeWeatherIntoDB completed, it will call the sendWeatherToServer via SQLdelegate. After sendWeatherToServer completed, I will a variable to notify checkWeathermethod.
Question: How checkWeathermethod wait all these process to complete so that it can return the variable?
(int)checkWeathermethod --call--> storeWeatherIntoDB
storeWeatherIntoDB carry out process
storeWeatherIntoDB delegate return --call--> sendWeatherToServer
sendWeatherToServer carry out process
sendWeatherToServer delegate return --notify--> checkWeathermethod to return int
I am thinking of using Notification center to notify checkWeathermethod but I don't know how to make it wait for the processes.
If not I wish to have a timer with 10 sec timeout if nothing return
If result return within 10 sec, checkWeathermethod will return the int.

Answer 1

One possible solution is to use blocks. For instance, if you want to execute code after storeWeatherIntoDB has finished, you can do it this way:
- (void)checkWeathermethod {
[self storeWeatherIntoDB:^(int returnCode) {
dispatch_async(dispatch_get_main_queue(), ^{
// When you get here, the weather has been stored on the server.
// E.g. you can now show success or failure here
if (returnCode == 0) {
// OK
}
else {
// Error
}
});
}];
}
- (void)storeWeatherIntoDB:(void(^)(int returnCode))completionBlock {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
// Store weather into db here.
// You can do this even synchronously.
int returnCode = [self storeWeather];
// Call callback
if (completionBlock) {
completionBlock(returnCode);
}
});
}