Question

简单地说，我想在UIAlertAction处理程序中从我的类中调用方法或引用变量。

我是否需要将块传递给此处理程序，还是有其他方法可以实现此目的？

@interface OSAlertAllView ()
@property (nonatomic, strong) NSString *aString;
@end

@implementation OSAlertAllView

+ (void)alertWithTitle:(NSString *)title message:(NSString *)msg cancelTitle:(NSString *)cancel inView:(UIViewController *)view
{
    __weak __typeof(self) weakSelf = self;

    UIAlertController *alert = [UIAlertController alertControllerWithTitle:title message:msg
                                                                preferredStyle:UIAlertControllerStyleAlert];
    UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:cancel style:UIAlertActionStyleDefault
        handler:^(UIAlertAction * action) {
            // I'd like to reference a variable or method here
            weakSelf.aString = @"Apples"; // Not sure if this would be necessary
            self.aString = @"Apples"; // Member reference type 'struct objc_class *' is a pointer Error
            [self someMethod]; // No known class method Error
        }];

    [alert addAction:defaultAction];
    [view presentViewController:alert animated:YES completion:nil];
}

- (void)someMethod {

}

Answer 1

+方法开头的alertWithTitle...表示它是一种类方法。当您调用它时，self将是类OSAlertAllView，而不是OSAlertAllView类型的实例。

有两种方法可以更改它以使其正常工作。

将方法开头的+更改为-，使其成为实例方法。然后你可以在实例而不是类上调用它。

// Old Class Method Way
[OSAlertAllView alertWithTitle:@"Title" message:@"Message" cancelTitle:@"Cancel" inView:viewController];

// New Instance Methods Way
OSAlertAllView *alert = [OSAlertAllView new];
[alert alertWithTitle:@"Title" message:@"Message" cancelTitle:@"Cancel" inView:viewController];

另一种方法是在OSAlertAllView内部alertWithTitle...创建一个实例，并将self替换为该对象。

+ (void)alertWithTitle:(NSString *)title message:(NSString *)msg cancelTitle:(NSString *)cancel inView:(UIViewController *)view
{
    OSAlertAllView *alertAllView = [OSAlertAllView new];

    UIAlertController *alert = [UIAlertController alertControllerWithTitle:title message:msg
                                                                preferredStyle:UIAlertControllerStyleAlert];
    UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:cancel style:UIAlertActionStyleDefault
        handler:^(UIAlertAction * action) {
            alertAllView.aString = @"Apples";
            [alertAllView someMethod];
        }];

    [alert addAction:defaultAction];
    [view presentViewController:alert animated:YES completion:nil];
}

如何在Objective-C中正确使用UIAlertAction处理程序

1 个答案: