selector | 易学教程

Are selectors in Objective-C just another way to send a message to an object?

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问题 Are selectors in Objective-C just another way to send a message to an object? I really don't understand why or how to use them. 回答1: They aren’t another way to send a message to an object, they’re the only way. For example, in [myView setValue:@"foo"] , setValue: is a selector. (Another, less convenient way of writing the same thing is objc_msgSend(myView, @selector(setValue:), @"foo") .) As Ian Henry says, you can use SEL values to choose a selector at runtime instead of compile time. This

Understanding Swift 2.2 Selector Syntax - #selector()

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问题 I am switching over the syntax of my project toward Swift 2.2 (which xCode helps me do automatically); however, I do not understand the new #selector() syntax. As an example: timer = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: #selector(MyVC.timerCalled(_:)), //new selector syntax! userInfo: nil, repeats: true) This has the selector #selector(MyVC.timerCalled(_:)) What does the _: signify? Can you add other variables into this selector? Say, #MyVC.timerCalled(_

[高并发Java 八] NIO和AIO

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> IO感觉上和多线程并没有多大关系，但是NIO改变了线程在应用层面使用的方式，也解决了一些实际的困难。而AIO是异步IO和前面的系列也有点关系。在此，为了学习和记录，也写一篇文章来介绍NIO和AIO。 1. 什么是NIO NIO是New I/O的简称，与旧式的基于流的I/O方法相对，从名字看，它表示新的一套Java I/O标准。它是在Java 1.4中被纳入到JDK中的，并具有以下特性： NIO是基于块（Block）的，它以块为基本单位处理数据（硬盘上存储的单位也是按Block来存储，这样性能上比基于流的方式要好一些）为所有的原始类型提供（Buffer）缓存支持增加通道（Channel）对象，作为新的原始 I/O 抽象支持锁（我们在平时使用时经常能看到会出现一些.lock的文件，这说明有线程正在使用这把锁，当线程释放锁时，会把这个文件删除掉，这样其他线程才能继续拿到这把锁）和内存映射文件的文件访问接口提供了基于Selector的异步网络I/O 所有的从通道中的读写操作，都要经过Buffer，而通道就是io的抽象，通道的另一端就是操纵的文件。 2. Buffer Java中Buffer的实现。基本的数据类型都有它对应的Buffer Buffer的简单使用例子： package test; import

Customizing tabs on state in Android

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问题 I know how to put the icon on each tab, that is no problem. I also ran across this : [Stack Overflow thread on pretty much same thing][1] I followed one of the links from that question and found [this][2] Pretty much, it said to use a selector defined in the XML, sure, did that. But there is no id associated w/ it so I am not sure how to get the selector function as a drawable so I can use it as the icon for the tabs. Maybe I am going about this the wrong way. But this is what I have, and

Android: textColor of disabled button in selector not showing?

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问题 I am trying to make a button with a selector my button can have the following states: Enabled/Disabled Pressed/Not Pressed According to the states mentioned above. I need to manipulate the button's: Text color background image The button starts off my being disabled so it should have the disabled textColor and the disabled button background. But I can see the default textColor (specified in style) and NO background image! Here is my selector button_selector.xml <?xml version="1.0" encoding=

When to use a colon with a @selector

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问题 Just getting going with iPhone development and Objective-C . Yesterday I was trying to addObserver for a notification in a view of mine, and I kept getting this error: unrecognized selector sent to instance I tracked it down to the fact that I needed to include the trailing colon to my selector argument: [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(nameOfMySelector:) name:@"BBLocationServicesAreDisabled" object:nil]; Today, I thought I was clever because when

Passing parameters to the method called by a NSTimer

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问题 How can I pass a parameter to the method called by a NSTimer? My timer looks like this: [NSTimer scheduledTimerWithTimeInterval:4 target:self selector:@selector(updateBusLocation) userInfo:nil repeats:YES]; and I want to be able to pass a string to the method updateBusLocation. Also, where am supposed to define the method updateBusLocation? In the same .m file that I create the timer? EDIT: Actually I am still having problems. I am getting the error message: Terminating app due to uncaught

Passing parameters on button action:@selector

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问题 I want to pass the movie url from my dynamically generated button to MediaPlayer: [button addTarget:self action:@selector(buttonPressed:) withObject:[speakers_mp4 objectAtIndex:[indexPath row]] forControlEvents:UIControlEventTouchUpInside]; but action:@selector() withObject: does not work? Is there any other solution? Thanks for help! 回答1: Edit. Found a neater way! One argument that the button can receive is (id)sender . This means you can create a new button, inheriting from UIButton, that

List selectors for Objective-C object

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问题 I have an object, and I want to list all the selectors to which it responds. It feels like this should be perfectly possible, but I'm having trouble finding the APIs. 回答1: This is a solution based on the runtime C functions: class_copyMethodList returns a list of class methods given a Class object obtainable from an object. #import <objc/runtime.h> [..] SomeClass * t = [[SomeClass alloc] init]; int i=0; unsigned int mc = 0; Method * mlist = class_copyMethodList(object_getClass(t), &mc); NSLog

What is the Swift equivalent of respondsToSelector?

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问题 I've googled but not been able to find out what the swift equivalent to respondsToSelector: is. This is the only thing I could find (Swift alternative to respondsToSelector:) but isn't too relevant in my case as its checking the existence of the delegate, I don't have a delegate I just want to check if a new API exists or not when running on the device and if not fall back to a previous version of the api. 回答1: As mentioned, in Swift most of the time you can achieve what you need with the ?