Question

For instance,If the image download from the server we should load the image lazily. and i want to know the other instances.

Answer 1

It couldn’t hurt to always do this. All of the devices coming out lately benefit from multi-core CPUs. Grand central dispatch makes it easy to define a process that will be executed on another core, and then synch it up to the main thread for UI udpates, when done.

If you do this your application will feel more responsive, and also will be easy to move from say local disk access to remote access of resources.

Example:

 dispatch_queue_t taskQ = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(taskQ, ^
    {
        //Do some work. . . . 

        //Now update back on the main thread
        dispatch_async(dispatch_get_main_queue(), ^
        {

        });
    });


    //release the queue.