Objective-C

Async Task Chain

See more Async Examples

Demonstrates how to combine a sequence of asynchronous tasks into a single task chain to be run in a background thread. Objective-C

#import <CkoMailMan.h>
#import <CkoTaskChain.h>
#import <CkoTask.h>
#import <CkoEmail.h>

BOOL success = NO;

// This example assumes the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

success = NO;

CkoMailMan *mailman = [[CkoMailMan alloc] init];

// Set the POP3 server's hostname
mailman.MailHost = @"pop.example.com";

// Set the POP3 login/password and any other requirements..
mailman.PopUsername = @"myLogin";
mailman.PopPassword = @"myPassword";
mailman.PopSsl = YES;
mailman.MailPort = [NSNumber numberWithInt:995];

// Connect to the POP3 server:
success = [mailman Pop3BeginSession];
if (!success) {
    NSLog(@"%@",mailman.LastErrorText);
    return;
}

// Get the number of messages in the mailbox.
int numMessages = [[mailman GetMailboxCount] intValue];
if (numMessages == 0) {
    NSLog(@"%@",@"No email messages in the POP3 mailbox.");
    return;
}

CkoTaskChain *taskChain = [[CkoTaskChain alloc] init];

// Create async task objects to fetch each email message
// by its sequence number
int i;
CkoTask *task = 0;

for (i = 1; i <= numMessages; i++) {

    task = [mailman FetchByMsgnumAsync: [NSNumber numberWithInt: i]];
    if (mailman.LastMethodSuccess == NO) {
        NSLog(@"%@",mailman.LastErrorText);
        return;
    }

    // Append each task to the task chain.
    success = [taskChain Append: task];
    if (!success) {
        NSLog(@"%@",taskChain.LastErrorText);
        return;
    }

}

// At this point, no tasks have actually started running.
// All we've done so far is to create tasks for the work that will be done
// when the task chain is run.

// Start the task chain running in a background thread.
// Each task is run one after the other (on the same background thread) until all tasks have completed.
// The task chain will stop at the first task that fails.
taskChain.StopOnFailedTask = YES;
success = [taskChain Run];
if (!success) {
    NSLog(@"%@",taskChain.LastErrorText);
    return;
}

// The application is now free to do anything else
// while the emails are being downloaded

// For this example, we'll simply sleep and periodically
// check to see if the taskchain if finished. 
while (taskChain.Finished != YES) {

    // Sleep 100 ms.
    [taskChain SleepMs: [NSNumber numberWithInt: 100]];

}

// A finished task chain could be one that was canceled, aborted, or truly finished.  

// If the task chain "completed", then it ran to completion.  A "completed" task will
// have a StatusInt equal to 7.   If the task finished, but was not completed, then it must've
// been aborted or canceled:
if ([taskChain.StatusInt intValue] != 7) {
    NSLog(@"%@",@"Task did not complete.");
    NSLog(@"%@%@",@"task chain status: ",taskChain.Status);
    return;
}

CkoEmail *email = [[CkoEmail alloc] init];

int numTasks = [taskChain.NumTasks intValue];
int taskIdx = 0;

while ((taskIdx < numTasks)) {

    task = [taskChain GetTask: [NSNumber numberWithInt: taskIdx]];

    // Load the email object with email downloaded by this task.
    success = [email LoadTaskResult: task];
    if (!success) {
        NSLog(@"%@",@"Failed to load email object for task.");
    }
    else {
        NSLog(@"%@%@%@",email.From,@"; ",email.Subject);
    }

    taskIdx = taskIdx + 1;
}