UIAlertController -- Capturing 'controller' strongly in this block - ios

Question

UIAlertController is crashing with this error message:
Attempting to load the view of a view controller while it is deallocating is not allowed and may result in undefined behavior (<UIAlertController: 0x7fb9107674d0>)
also with a warning is thrown trying to capture the textFields objectAtIndex.
Any ideas ?
Warning.. Capturing 'controller' strongly in this block is likely to lead to a retail cycle.
I also tried to create a #property (weak) reference the warning goes away but the app still crashes with this:
-(void)viewWillAppear:(BOOL)animated
{
// self.controller = [UIAlertController alloc];
UIAlertController* controller = [UIAlertController alertControllerWithTitle:#"Add Alergy To List" message:nil preferredStyle:(UIAlertControllerStyleAlert)];
[controller addTextFieldWithConfigurationHandler:^(UITextField * nametextField) {
_nameTextField.text = [controller.textFields objectAtIndex:0].text;
}];
UIAlertAction *save = [UIAlertAction actionWithTitle:#"Save Data" style:(UIAlertActionStyleDefault) handler:^(UIAlertAction * _Nonnull action) {
[self save:nil];
}];
UIAlertAction *cancel = [UIAlertAction actionWithTitle:#"Cancel Action" style:(UIAlertActionStyleCancel) handler:nil];
[controller addAction:save];
[controller addAction:cancel];
[self presentViewController:controller animated:YES completion:nil];
}

Answer 1

__weak __typeof(UIAlertController) weakController = controller;
__weak __typeof(UITextField) weakTextField = _nameTextField;
[controller addTextFieldWithConfigurationHandler:^(UITextField *nametextField){
// nameTextField is the textField being returned in the block
// if you want to use _nameTextField you need to make that weak too
nameTextField.text = [weakController.textFields objectAtIndex:0].text;
// or
weakTextField.text = [weakController.textFields objectAtIndex:0].text;
}];

Answer 2

Add
__weak __typeof(UIAlertController) weakController = controller;
before your addTextFieldWithConfigurationhandler:.
Then you should replace
_nameTextField.text = [controller.textFields objectAtIndex:0].text;
with
nameTextField.text = [weakController.textFields objectAtIndex:0].text;
Without the _.
_ is for internal access of properties. Here you have to update the field given in parameter
The fact is that you are in a block and if you want to get text from controller fields, you have to make a weak reference to it. The weak controller will prevent increase retain count.

Answer 3

You are trying to load alertcontroller before the viewcontroller is allocated this warning is because you are adding UIAlertController directly inside viewWillAppear
This method is called before the view controller's view is about to be added to a view hierarchy
Just give some time for view to get added to the view hierarchy.to do that use dispatch_after or some other delay functionality.
Since you are getting textfield input inside a block you can't use strong declaration,So you have to declare __weak typeof(UIAlertController) *weakcontroller = controller; before entering the block.Check apple developer site here for more understanding.
Overall modified code is given bekow:
-(void)viewWillAppear:(BOOL)animated{
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
UIAlertController* controller = [UIAlertController alertControllerWithTitle:#"Add Alergy To List" message:nil preferredStyle:(UIAlertControllerStyleAlert)];
__weak typeof(UIAlertController) *weakcontroller = controller;
[controller addTextFieldWithConfigurationHandler:^(UITextField * nametextField) {
nametextField.text = [weakcontroller.textFields objectAtIndex:0].text;
}];
UIAlertAction *save = [UIAlertAction actionWithTitle:#"Save Data" style:(UIAlertActionStyleDefault) handler:^(UIAlertAction * _Nonnull action) {
[self save:nil];
}];
UIAlertAction *cancel = [UIAlertAction actionWithTitle:#"Cancel Action" style:(UIAlertActionStyleCancel) handler:nil];
[controller addAction:save];
[controller addAction:cancel];
[self presentViewController:controller animated:YES completion:nil];
});
}
It will work without any issues.