ios block example. how to create block objective-c

Question

I have got two UIViewController:

MainVC
PickerVC

In main view controller I have IBAction method: - showPickerView

In this method I need to create block that will present PickerVC view and wait me while I choose something value on PickerVC view and press Done button.

In this block I need to implement callback that will invoke method in MainVC after I press on button Done.

So, I have used block before, but I don't know how to implement it by myself.

I think first part will be look like this:

- (IBAction)showPickerView {
   __block PickerVC *pickerVC = [[PickerVC alloc] init];
   [pickerVC setFinishBlock:^{
      // Do something after user press on Done button
   }];
   [pickerVC setFailedBlock:^{
      // Do something if something wrong (but this method optional)
   }];
   [pickerVC showPicker];
}

if you need a callback why don't you try to create a protocol and use the delegate scheme? or why don't you use the NSNotificationCenter...? — holex
– holex, Commented Jul 26, 2012 at 10:50

zeiteisen · Accepted Answer · 2012-07-26 09:54:45Z

7

Add in the header of PickerVC two typedefs

typedef void (^FinishBlock)();
typedef void (^FailedBlock)();

and your declaration of setFinishedBlock takes the FinishBlock

- (void)setFinishBlock:(FinishBlock)finishBlock;
- (void)setFailedBlock:(FailedBlock)failedBlock;

Make an iVar for each block

@interface PickerVC : UIViewController
{
  FinishBlock _finishBlock;
  FailedBlock _failedBlock;
}

In your definition of setFinishedBlock: and setFailedBlock: set the parameter to the iVars

As soon as PickerVC fails or finishes call _failedBlock or _finishedBlock.

The __block statement is used for variables to stay in memory if they are used in a block. So you don't need it in the above code

answered Jul 26, 2012 at 9:54

zeiteisen

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2 Comments

zeiteisen Over a year ago

like a c function _failedBlock();

Christopher Pickslay Over a year ago

Make sure to check for nil first: if (_failedBlock) _failedBlock();

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