block | 易学教程

Changing an instance variable in a block

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问题 I am quite confused about how to change an instance variable inside of a block. The interface file (.h): @interface TPFavoritesViewController : UIViewController { bool refreshing; } The implementation: __weak TPFavoritesViewController *temp_self = self; refreshing = NO; [myTableView addPullToRefreshWithActionHandler:^{ refreshing = YES; [temp_self refresh]; }]; As you might guess, I get a retain cycle warning when I try to change the refreshing ivar inside of the block. How would I do this

Changing an instance variable in a block

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Serializing asynchronous methods

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问题 I have a number of tasks I need to execute serially but the task includes next block in a completion block. What is a good technique for doing these tasks one at a time, starting the next task after the current one completes its completion block? Is there a technique other than a NSOperation subclass with a serial NSOperationQueue? 回答1: Standard solutions: NSOperationQueue with maxConcurrentOperationCount of 1 . You say you don't want to do that, but you don't say why. Serial queues are the

Can I reference a lambda from within itself using Ruby?

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问题 I want to be able to call an anonymous lambda from within itself using Ruby. Consider the following recursive block (returns a factorial). I know I can assign it to a variable, and that variable is within the scope of the lambda: fac = lambda { |n| n == 1 ? 1 : n * fac.call(n - 1) } fac.call(5) But, I want to be able to do the following (for no practical reason as of yet, I'm just interested in exploring the language some more): (lambda { |n| n == 1 ? 1 : n * self.call(n - 1) }).call(5) I

HDFS 读写流程

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http://blog.endlesscode.com/2010/06/16/hdfs-short-intro/ 一、HDFS HDFS全称是Hadoop Distributed System。HDFS是为以流的方式存取大文件而设计的。适用于几百MB，GB以及TB，并写一次读多次的场合。而对于低延时数据访问、大量小文件、同时写和任意的文件修改，则并不是十分适合。目前HDFS支持的使用接口除了Java的还有，Thrift、C、FUSE、WebDAV、HTTP等。HDFS是以block-sized chunk组织其文件内容的，默认的block大小为64MB，对于不足64MB的文件，其会占用一个block，但实际上不用占用实际硬盘上的64MB，这可以说是HDFS是在文件系统之上架设的一个中间层。之所以将默认的block大小设置为64MB这么大，是因为block-sized对于文件定位很有帮助，同时大文件更使传输的时间远大于文件寻找的时间，这样可以最大化地减少文件定位的时间在整个文件获取总时间中的比例。构成HDFS主要是Namenode（master）和一系列的Datanode（workers）。Namenode是管理HDFS的目录树和相关的文件元数据，这些信息是以"namespace image"和"edit log"两个文件形式存放在本地磁盘

学习C/C++的第十八天构建俄罗斯方块小游戏框架

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到过年了走亲访友又花去两天，进度又落下了今天学习了俄罗斯方块小游戏 /*这是头文件*/ # define BLOCK_COUNT 5 //数量 # define BLOCK_WIDTH 5 //宽度 # define BLOCK_HEIGHT 5 //高度 # define BLOCK_SIZE 20 //方块的像素大小 # define START_X 130 //掉落方块位置的X轴 # define START_Y 30 //掉落方块位置的Y轴 # define KEY_UP 72 //按键的 ↑ → ← 的对应ALLS值 # define KEY_RIGHT 77 # define KEY_DOWN 78 # define KEY_LEFT 75 int block [ BLOCK_COUNT * 4 ] [ BLOCK_HEIGHT ] [ BLOCK_WIDTH ] = //[三种 * 形态][行][列] { //条形方块 { 0 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 0 , 0 , 0 , 0 , 1 , 0 , 0 , 0 , 0 , 1 , 0 , 0 , 0 , 0 , 0 , 0 , 0 } , { 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 0 , 0 , 0 , 0

Why do NSBlocks have to be copied for storage in containers?

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问题 - (void) addABlock { void (^aBlock)(void) = ^() { [someObject doSomething]; }; [self.myMutableArray addObject: aBlock]; // Oops.. [self.myMutableArray addObject: [aBlock copy]]; // works fine } In the above simplified example I am seeing undefined behavior if the block copy is not performed. This case is specifically listed in apple's ARC transition guide. The part that I do not understand is why I have to manually call copy. The block is created on the stack so a block_copy needs to be

jquery validator plugin with display:none form elements

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问题 I'm using the validator plugin found here to validate a form. Problem I'm having is if I put the following around a form input element the validation fails: <div style="display:none;"><input type="text" name="test" /></div> I need this because I'm using other UI control layers for the input elements and don't want them visible. It works on inline and block elements, but I need it to be hidden. Is there anyway to get around this? Thanks for any feedback Update: I'm mostly validating select

HDFS读写数据流程

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HDFS读写数据流程标签（空格分隔）： Apache Hadoop HDFS是hadoop重要的组件之一，对其进行数据的读写是很常见的操作，然而真的了解其读写过程吗？前言 HDFS – Hadoop Distributed File System，是hadoop的存储层，它参照google的GFS思想实现。它以master-slave工作。NameNode作为master daemon，工作在master node上，DataNode作为slave daemon，工作在slave node上。master 之间在 HDFS 2.X.X 版本实现HA 高可用。一，写HDFS 1. 流程图 2. 重要概念 HDFS一个文件由多个block构成。或者说一个文件会被切分成按照HDFS block 大小的多个块去存储。 HDFS在进行block读写的时候是以packet(默认每个packet为64K)为单位进行的。每一个packet由若干个chunk（默认512Byte）组成。Chunk是进行数据校验的基本单位，对每一个chunk生成一个校验和(默认4Byte)并将校验和进行存储。在写入一个block的时候，数据传输的基本单位是packet，每个packet由若干个chunk组成。 3. 过程步骤 1） HDFS

How to stop enumerateObjectsUsingBlock Swift

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问题 How do I stop a block enumeration? myArray.enumerateObjectsUsingBlock( { object, index, stop in //how do I stop the enumeration in here?? }) I know in obj-c you do this: [myArray enumerateObjectsUsingBlock:^(id *myObject, NSUInteger idx, BOOL *stop) { *stop = YES; }]; 回答1: In Swift 1: stop.withUnsafePointer { p in p.memory = true } In Swift 2: stop.memory = true In Swift 3 - 4: stop.pointee = true 回答2: This has unfortunately changed every major version of Swift. Here's a breakdown: Swift 1