subclass | 易学教程

Why can't I subclass tuple in python3?

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问题 Let's preface this question by saying that you should use __new__ instead of __init__ for subclassing immutable objects. With that being said, let's see the following code: class MyTuple(tuple): def __init__(self, *args): super(MyTuple, self).__init__(*args) mytuple = MyTuple([1,2,3]) This works in python2, but in python3 I get: Traceback (most recent call last): File "tmp.py", line 5, in <module> mytuple = MyTuple([1,2,3]) File "tmp.py", line 3, in __init__ super(MyTuple, self).__init__(

Manage a UIPickerView from an External Class - Using Swift

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问题 I cannot seem to find the connection to have an external class manage a view in a ViewController. I'm new to iOS and have spent considerable looking for a solution. Simple Example: Subclass of UIPickerView I create a file that is a subclass of UIPickerView and have it conform to the PickerView delegate and datasource. class MyPickerView: UIPickerView, UIPickerViewDelegate, UIPickerViewDataSource { //In here I conform to all the required methods...no problems there } Main View Controller with

Java: Can a class inherit from two super classes at the same time?

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I have a class Journey which I want to make a superclass and another class plannedjourney. The plannedjourney class extends JFrame since it contains forms..However I also want this class to extends Journey.. Is there a possible way to do this? Don't mix models and views. If you keep both domains clearly separated, then you won't be in need of multiple inheritance (this time). You have one model class for journeys and a viewer for such journeys. The viewer should subclass Component and be displayed (somewhere) in your window (a JFrame instance). This viewer takes one journey object and presents

Delphi TListBox OnClick / OnChange?

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问题 Is there a trick to getting "OnChange" type of functionality with a TListBox? I can subclass the component and add a property, etc then only carry out OnClick code if the Index changes... I can also hack it with a form level variable to store the current index but just wondering if I'm overlooking the obvious before I go one way or the other. 回答1: There seems to be no way other than implementing this by yourself. What you need is to remember the currently selected item and whenever the

Is there any reason why we don't use subclasses of UIImageView?

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I'm currently trying to create a subclass of UIImageView in order to make it download its image from server asynchronously ;) I tried to do it by myself but I haven't gone very far yet :D Anyway, I looked around here and found this : AsyncImageDownload I had a look at the code and the first which springs to mind is : why subclassing a UIView and not a UIImageView ?!? Any thoughts ? Cheers mates, Gotye. Nir Levy The reason it is subclassing UIView is so that you should, for example, display a UIActivityIndicator while the image is being downloaded. They do not show this in their example but I

how does jquery return an array of the selected elements

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I have just seen a google tech talk presented by John Resig where he said jQuery operates as an array. Following that advice I have been playing with a subclassed array and it works great but I have been looking through the jQuery source and can't see that they have used the same method of jQuery.prototype = new Array(); And I can't see it even taking the native Array.prototype.methods with call/apply or in the prototype chain in the window.$ object, so I am wondering how does the jQuery object return an array of the selected elements. I have tried using an ordinary object, but if returning an

Subclassing class from shared library compiled with -fno-rtti

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问题 I am trying to subclass from a shared library which was compiled with -fno-rtti. Unfortunately other libraries in my code base require -frtti. As a result I am getting link errors because the superclass does not have a typeinfo struct. Error received in a normal compilation: out.o: in function typeinfo for MyClass:myclass.cpp(.data.rel.ro.<cpp magic>): error: undefined reference to 'typeinfo for NetlinkListener' The class I want to subclass is an android class in libsysutils (snipped a little

Load a AQGridViewCell from XIB (not working)

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I am using AQGridView class and I am trying to load a cell from an XIB . I have setup the XIB like a Custom Cell for a UITableView , but when I attempt to load the cell, it is simply blank. I was wondering if there was an easier way to get the XIB to load. AQGridViewCell need to load the cell from an xib - (AQGridViewCell *) gridView: (AQGridView *) gridView cellForItemAtIndex: (NSUInteger) index { static NSString * CellIdentifier = @"cellID"; gridCell * cell = (gridCell *)[gridView dequeueReusableCellWithIdentifier: CellIdentifier]; if ( cell == nil ){ gridCell = [[gridViewCell alloc]

Multiple subclasses, how to instance any of them?

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This will be a bit hard to explain, but I will try my best. I want to have multiple items that, when clicked, each have a different result. For the rest, they all have the same variables. So basically, I have a class Item, and subclasses Ball, Rope, Book, and many, many more to come. I want to be able to easily add items if I want to. The Item class has a String name, String description and a method 'onUse' that each of the subclasses override. I would like to handle this as dynamical as possible, meaning I would like a single method in my Frame/Activity (This is for Android but Java applies)

Multiple restrictions on generic type based on super and sub classes in java

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I have a generic list class that implements a particular interface. The list items in the interface also implement the same interface. public abstract class List<T extends SomeInterface> implements SomeInterface { protected LinkedList<T> m_list; ... } So now I want to make a subclass of this list that stays generic but limits the items to objects that implement the SearchListItem interface: public interface SearchListItem { public String getName(); } Here's what I have for the SearchList class so far: public abstract class SearchList<T extends SearchListItem> extends List<T> { public T get