iOS Objective-C block callback issue - ios

Question

I am trying to use pure code to create UI practice block pass value between viewController. But the callback block didn't work. The NSLog method didn't print anything on debug area. Here's the code. Give me some tips, thank you.
VC.h
#import <UIKit/UIKit.h>
#interface SecondViewController : UIViewController
#property (copy, nonatomic) void (^callBack)(NSString *text);
#end
VC.m
- (UITextField *)textField {
if (!_textField) {
_textField = [[UITextField alloc] init];
_textField.backgroundColor = [UIColor whiteColor];
}
return _textField;
}
- (UIButton *)button {
if (!_button) {
_button = [[UIButton alloc] init];
_button.backgroundColor = [UIColor blueColor];
[_button addTarget:self action:#selector(buttonAction) forControlEvents:UIControlEventTouchUpInside];
}
return _button;
}
- (void)setupUI {
[self.view addSubview:self.textField];
[self.view addSubview:self.button];
[self.textField mas_makeConstraints:^(MASConstraintMaker *make) {
make.width.mas_equalTo(200);
make.height.mas_equalTo(50);
make.centerX.mas_equalTo(self.view.mas_centerX);
make.centerY.mas_equalTo(self.view);
}];
[self.button mas_makeConstraints:^(MASConstraintMaker *make) {
make.width.mas_equalTo(200);
make.height.mas_equalTo(50);
make.centerX.mas_equalTo(self.view);
make.centerY.mas_equalTo(self.view).offset(100);
}];
}
- (void)buttonAction {
NSString *str = self.textField.text;
if (self.callBack != nil) {
self.callBack(str);
NSLog(#"This statement didnt print in log");
}
}
- (void)viewDidLoad {
[super viewDidLoad];
[self setupUI];
// Do any additional setup after loading the view.
self.view.backgroundColor = [UIColor redColor];
}
update code
VC2.m
- (void)viewWillAppear:(BOOL)animated{
self.callBack = ^(NSString *text){
};
}
- (void)buttonAction {
if (self.callBack) {
NSLog(#"It worked on debug area %#", self.textField.text);
self.callBack(self.textField.text);
}
self.textField.text = #"";
}
VC1.m
- (void)viewDidLoad {
[super viewDidLoad];
_secondVc = [[SecondViewController alloc] init];
_secondVc.callBack = ^(NSString *str){
};
[self setupUI];
self.view.backgroundColor = [UIColor greenColor];
}
- (void)viewWillAppear:(BOOL)animated {
if (_secondVc.callBack != nil) {
NSLog(#"It wrked on debug screen");
_secondVc.callBack = ^(NSString *str){
NSLog(#"It didn't worked on debug screen");
//I want set my label.text = str;
};
};
}

Answer 1

The only way is that you property
#property (copy, nonatomic) void (^callBack)(NSString *text);
is empty. Try to put breakpoint in buttonAction method and look at the property.

Answer 2

As Sander and KrishnaCA mentioned your callBack is nil. I would suggest you create a definition of the block like this:
typedef void(^TextBlock)(NSString *text);
Then change your property to:
#property (copy, nonatomic) TextBlock callBack;
Create a copy of the block in your first view controller:
#interface FirstViewController()
#property (copy, nonatomic) TextBlock firstViewControllerCallBack;
#end
Initialize the callback copy (i.e. in viewDidLoad)
- (void)viewDidLoad {
[super viewDidLoad];
self.firstViewControllerCallBack = ^(NSString *text){
NSLog(#"Second view controller's button tapped!");
};
}
Assign the callback to the second view controller right before presenting/pushing it:
SecondViewController *secondVC = [[SecondViewController alloc] init];
secondVC.callBack = self.firstViewControllerCallBack; // Assign the callback
// ... Presenting the view controller
Clean up the completion block after you done with it (i.e. in viewWillDisappear):
- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
self.firstViewControllerCallBack = nil;
}