kotlin，如何向已定义的类伴随对象添加扩展函数

Question

我想为已经定义的类的伴随对象添加一些扩展函数，比如

fun Toast.Companion.showImageToast(str : String) {
}

我也喜欢在界面上做同样的事情，例如

fun Runnable.Companion.mainHandler() {
}

我已经查阅了文档，只是为用户定义的类中的伴随对象找到定义扩展函数的语法，而不是没有伴随对象的类

我可以在kotlin有机会这样做吗？

Answer 1

在Kotlin 1.0中，如果某个类没有定义伴随对象，则无法为该伴随对象定义扩展函数。也无法为Java类和接口定义扩展函数，例如- (NSPersistentStoreCoordinator *)persistentStoreCoordinator { // The persistent store coordinator for the application. This implementation creates and return a coordinator, having added the store for the application to it. if (_persistentStoreCoordinator != nil) { return _persistentStoreCoordinator; } // Create the coordinator and store _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]]; // *** add support for light weight migration *** NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil]; NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"StoreName.sqlite"]; NSError *error = nil; // *** Add support for lightweight migration by passing options value *** if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:options error:&error]) { // Replace this with code to handle the error appropriately. // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. NSLog(@"Unresolved error %@, %@", error, [error userInfo]); } return _persistentStoreCoordinator; } 。