subclass

问题 I am trying to subclass WKWebView. When I implement my own initializer, I got this error: 'required' initializer 'init(coder:)' must be provided by subclass of 'WKWebView' Ok, that is well known that we have to implement it for subclasses of UIView. For a direct subclass of UIView it works just implementing it, but with WKWebView it does not seem so simple. I followed the Fix-it hint, and this snippet is added to the code: required @availability(*, unavailable) convenience init!(coder:

问题 I want to write a function that works on any Scala type with a total ordering (i.e. I can use '<' on it). What's the syntax for that? The best I've come up with is def lessThan[T <: Ordered[T]](x: T, Y: T) = x < y That doesn't work, though, when I try using it from the REPL: scala> lessThan(1, 2) <console>:8: error: inferred type arguments [Int] do not conform to method lessThan's type parameter bounds [T <: Ordered[T]] lessThan(1, 2) ^ scala> import runtime._ import runtime._ scala> lessThan

问题 In Java, is it possible to override member data in a subclass and have that overridden version be the data used in a super class's implementation? In other words, here's what I am trying to get to happen, and it's not happening: abstract public class BasicStuff { protected String[] stuff = { "Pizza", "Shoes" }; public void readStuff() { for(String p : stuff) { system.out.println(p); } } } .. public class HardStuff extends BasicStuff { protected String[] stuff = { "Harmonica", "Saxophone",

问题 I have created a class that extends Array. I want to execute arbitrary code before calling the inherited push function. class newArray extends Array{ //execute any logic require before pushing value onto array this.push(value) } 回答1: The solution I found was to create a new function in the subclass that has the same name as the inherited function. In this case push. Then inside the overriding function the inherited function is called via the super keyword. class newArray extends Array{ push

问题 My goal is to set the textColor of my custom UILabel subclass in my view controller. I have a UILabel subclass named CircleLabel . Here are the basics of it: class CircleLabel: UILabel { required init(coder aDecoder: NSCoder) { super.init(coder: aDecoder)! } override init(frame: CGRect) { super.init(frame: frame) } override func drawRect(rect: CGRect) { self.layer.cornerRadius = self.bounds.width/2 self.clipsToBounds = true super.drawRect(rect) } override func drawTextInRect(rect: CGRect) {

问题 I have a class called BankAccount as base class. I also have CheckingAccount and SavingsAccount classes that inherit from BankAccount . BankAccount is not an abstract class but I do not create an object from it, only the inheriting classes. Then, I execute a query like this: account = BankAccount.objects.get(id=10) How do I know if account is CheckingAccount or SavingsAccount ? The way I do this now is in this way: checking_account = CheckingAccount.objects.get(id=account.id) If it exists, it

问题 I finally upgraded my python version and I was discovering the new features added. Among other things, I was scratching my head around the new __init_subclass__ method. From the docs: This method is called whenever the containing class is subclassed. cls is then the new subclass. If defined as a normal instance method, this method is implicitly converted to a class method. So I started to playing around with it a little bit, following the example in the docs: class Philosopher: def __init

问题 This question already has answers here : What does it mean to “program to an interface”? (31 answers) Closed 3 years ago . List<String> list = new ArrayList<String>(); What is List and ArrayList when identifying the parts besides super class and subclass? Is List the reference and ArrayList the class? Would they be called something else if they were the same like: ArrayList<String> list = new ArrayList<String>(); 回答1: List is an interface. ArrayList is an implementation of it. Neither is a

问题 I tried to subclass Button , but I have a lot of errors when launching my project. Could you have a look and tell me how to fix this? (I've got maybe 50 errors coming up) package my.project.name; import android[...] public class MyButton extends Button { public MyButton(){ super(null); } public MyButton(Context context){ super(context); } public MyButton(Context context, AttributeSet attrs){ super(context, attrs); } public MyButton(Context context, AttributeSet attrs, int defStyle){ super

问题 When in "edit" or "show" this comes up: ActiveRecord::SubclassNotFound in Registries#edit "The single-table inheritance mechanism failed to locate the subclass: 'Plane'. This error is raised because the column 'type' is reserved for storing the class in case of inheritance. Please rename this column if you didn't intend it to be used for storing the inheritance class or overwrite Present.inheritance_column to use another column for that information." 25: </div> 26: 27: <div class="field1"> 28