Objective-C category.md

Objective-C category

開一組新的檔案 UIViewController+Alert.h、UIViewController+Alert.m 分別放以下內容：

`UIViewController+Alert.h`

#import <UIKit/UIKit.h>

@interface UIViewController (Alert)

- (void)presentAlertWithTitle:(NSString *)title 
                      message:(NSString *)message;

@end

`UIViewController+Alert.m`

#import "UIViewController+Alert.h"

@implementation UIViewController (Alert)

- (void)presentAlertWithTitle:(NSString *)title
                      message:(NSString *)message
{
    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title
                                                                             message:message
                                                                      preferredStyle:UIAlertControllerStyleAlert];
    
    [alertController addAction:[UIAlertAction actionWithTitle:@"OK"
                                                        style:UIAlertActionStyleCancel
                                                      handler:nil]];
    
    [self presentViewController:alertController
                       animated:YES
                     completion:nil];
}

@end

在別的 ViewController 就可以用以下方法呼叫：

#import "UIViewController+Alert.h"

@implementation MyViewController

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    [self presentAlertWithTitle:@"Oops!"
                        message:@"This app is about to crash!"];
}

@end

如果很常用的話可以考慮在 precompiled prefix header 裡面 import UIViewController+Alert.h。

extension UIViewController { func presentAlertWith(title title: String!, message: String!) { let alertController = UIAlertController( title: title, message: message, preferredStyle: .Alert ) alertController.addAction( UIAlertAction( title: "OK", style: .Cancel, handler: nil ) ) self.presentViewController( alertController, animated: true, completion: nil ) } }

class MyViewController: UIViewController { ... override func viewDidAppear(animated: Bool) { super.viewDidAppear(animated) self.presentAlertWith( title: "Oops!", message: "This app is about to crash!" ) } ... }

Objective-C

- (void)presentAlertWithTitle:(NSString *)title
                      message:(NSString *)message
                      handler:(void(^)(UIAlertAction *action))actionHandler
{
    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title
                                                                             message:message
                                                                      preferredStyle:UIAlertControllerStyleAlert];

    [alertController addAction:[UIAlertAction actionWithTitle:@"OK"
                                                        style:UIAlertActionStyleCancel
                                                      handler:actionHandler]];

    [self presentViewController:alertController
                       animated:YES
                     completion:nil];
}

Swift

func presentAlertWith(title title: String!, message: String!, actionHandler: ((UIAlertAction) -> Void)?) {
        let alertController = UIAlertController(
            title: title,
            message: message,
            preferredStyle: .Alert
        )

        alertController.addAction(
            UIAlertAction(
                title: "OK",
                style: .Cancel,
                handler: actionHandler
            )
        )

        self.presentViewController(
            alertController,
            animated: true,
            completion: nil
        )
}

[self presentAlertWithTitle:@"Oops!" message:@"Something went wrong!" handler:^(UIAlertAction *action) { // do something }];

/Objective-C category.md Secret