CODEWITHSUNDEEP
iosobjective-ccocoa-touchuibutton
Sam B
Sam B

Reputation: 27598

cannot press UIButton if for loop is running

This was pretty werid and I am sure I am missing something basic here.

What I have are

What happening is that when I press button1 then for-loop starts. I cannot press any more buttons on the screen till this for-loop ends i.e. I cannot press down on button2.

How can I make it so that when I press button1 I still have the ability to cancel that for-loop action of button1 by pressing button2. Here is my code

static bool scanCancelled = NO;

-(IBAction)startAction
{
    for (int i=0; i<5000; i++)
    {  
        NSLog(@"i: %d ...", i);

        if (scanCancelled == YES)
        {
            break;
        }
    }//end for-loop
} 

-(IBAction)cancelAction
{
    scanCancelled = YES;
}

For anyone interested in future this is how I did it

-(IBAction)startAction2
{
    //reset it
    scanCancelled = NO;

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
                                             (unsigned long)NULL), ^(void) {
        [self startAction];

    });

}

Upvotes: 2

Views: 182

Answers (3)

IanStallings
IanStallings

Reputation: 816

As others have said, you have to use another thread/process to run the long running for loop, so the UI can continue handling events, etc.

But I don't recommend using the threading classes in iOS, which can seem a little obtuse unless you are used to multi-threading*, instead I recommend using Grand Central Dispatch: https://developer.apple.com/library/ios/documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html

Using it is quite easy and will introduce you to blocks, which are very powerful. Here is a tutorial to get you started: http://www.raywenderlich.com/4295/multithreading-and-grand-central-dispatch-on-ios-for-beginners-tutorial

*That all being said, you should look into typical threading models and how they work. The concepts are in use well beyond iOS and Objective-C.

Upvotes: 2

dbiagi
dbiagi

Reputation: 85

You can start a new thread to execute the for loop.

Upvotes: 0

Armand
Armand

Reputation: 10254

You will have to run that long running operation from a separate thread to open the Main UI Thread for user interaction.

Then you can send a cancel message to your other thread from the action of button 2.

Upvotes: 0

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