ios – 从不兼容类型’ViewController * const__strong’分配给’id’

我的应用程序中有一个 ImagePickerController.
它效果很好,但除了ipc.delegate = self之外;出现错误消息：

Assigning to
‘id’
from incompatible type ‘ViewController *const__strong’

该应用程序运行良好,所以我忽略了错误消息,但我想我需要知道原因.为什么会出现错误消息？

ipc = [[UIImagePickerController alloc]init];
            ipc.modalPresentationStyle = UIModalPresentationCurrentContext;
            ipc.delegate = self;
            ipc.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
            [ipc setAllowsEditing:NO];
            [self presentViewController:ipc animated:NO completion:nil];

解决方法

如果你看一下UIImagePickerController委托属性的定义,你会看到它被定义为：

@property(nonatomic,assign) id<UINavigationControllerDelegate,UIImagePickerControllerDelegate> delegate

您设置为委托的任何对象(在这种情况下,您使用self)必须符合UINavigationControllerDelegate协议和UIImagePickerControllerDelegate协议.如果对象不符合这两个协议,您将收到编译时警告.

以下是您声明您的类符合协议的方式：

@interface MyViewController : UIViewController <UINavigationControllerDelegate,UIImagePickerControllerDelegate>

阅读working with protocols,UINavigationControllerDelegate和UIImagePickerControllerDelegate.