nsstring | 易学教程

Convert NSString of a math equation to a value

阅读更多关于 Convert NSString of a math equation to a value

问题 I would like to know how to evaluate a string representation of an equation as if it were a real equation: if(@"15+14==23") { //True statement... } else { //False statement.... } I want to return "false" because 15+14 does not equal 23. How can I get this to work? 回答1: Here is an example how to do it with NSPredicate : NSPredicate *p = [NSPredicate predicateWithFormat:@"1+2==3"]; NSLog(@"%d", [p evaluateWithObject:nil]); p = [NSPredicate predicateWithFormat:@"1+2==4"]; NSLog(@"%d", [p

NSPredicate for an NSManagedObject's string attribute's length

阅读更多关于 NSPredicate for an NSManagedObject's string attribute's length

问题 Could someone please help me define a predicate that returns only NSManagedObject's who's "letters" attribute length is within a certain range? Here's the example I've been trying, I've got a feeling it's the letters.length notation, I've also tried the kvc letters.@length with no success.. What am I doing wrong? NSManagedObjectContext *context = ...; NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Word"

Get the extension of a file contained in an NSString

阅读更多关于 Get the extension of a file contained in an NSString

问题 I have an NSMutable dictionary that contains file IDs and their filename+extension in the simple form of fileone.doc or filetwo.pdf. I need to determine what type of file it is to correctly display a related icon in my UITableView. Here is what I have done so far. NSString *docInfo = [NSString stringWithFormat:@"%d", indexPath.row]; //Determine what cell we are formatting NSString *fileType = [contentFiles objectForKey:docInfo]; //Store the file name in a string I wrote two regex to determine

Reliable way to compare two NSURL or one NSURL and an NSString?

阅读更多关于 Reliable way to compare two NSURL or one NSURL and an NSString?

问题 I recently had a problem when comparing two NSURLs and compare one NSURL with an NSString(which is a URL address), the situation is I got an NSURLRequest from somewhere, I may or may not know the URL address it points to, and I have an URL NSString, say "http://m.google.com", now I need to check if the URL in that NSURLRequest is the same as the URL string I had: [[request.URL.absoluteString lowercaseString] isEqualToString: [self.myAddress lowercaseString]]; this returns NO as the

NSPredicate

阅读更多关于 NSPredicate

一、简介　　NSPredicate 指定数据被获取或者过滤的方式，是一个Foundation类。　　Cocoa框架中的NSPredicate用于指定过滤器的条件（即查询），它的原理和用法都像SQL的 WHERE 和正则表达式一样，作用相当于数据库的过滤器。　　最常用到的函数：+ predicateWithFormat: 创建谓词串 + (NSPredicate *)predicateWithFormat:(NSString *)predicateFormat, ...; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name == 'Herbie'"]; //注意:如果谓词串中的文本块未被引用,则被看做是键路径,即需要用引号表明是字符串,单引号,双引号均可.键路径可以在后台包含许多强大的功能　　二、谓词语法范例数据源：索引 0 1 2 3 名 Alice Bob Charlie Quentin 姓 Smith Jones Smith Alberts 年龄 24 27 33 31 背景： @interface Person : NSObject @property NSString *firstName; @property NSString *lastName; @property

iOS中的谓词（NSPredicate）使用

阅读更多关于 iOS中的谓词（NSPredicate）使用

iOS中的谓词（NSPredicate）使用首先，我们需要知道何谓谓词，让我们看看官方的解释: The NSPredicate class is used to define logical conditions used to constrain a search either for a fetch or for in-memory filtering. NSPredicate类是用来定义逻辑条件约束的获取或内存中的过滤搜索。可以使用谓词来表示逻辑条件，用于描述对象持久性存储在内存中的对象过滤。其实意思就是：我是一个过滤器，不符合条件的都滚开。一、NSPredicate的基本语法我们使用一门语言，无论是外语还是计算机语言，总是从语法开始的，这样我们才能正确的把握逻辑。所以我们从语法开始说起。在这部分我们仅关心其语法的使用只要我们使用谓词（NSPredicate）都需要为谓词定义谓词表达式 ,而这个表达式必须是一个返回BOOL的值。谓词表达式由表达式、运算符和值构成。 1.比较运算符比较运算符如下 =、==：判断两个表达式是否相等，在谓词中=和==是相同的意思都是判断，而没有赋值这一说 NSNumber *testNumber = @123; NSPredicate *predicate = [NSPredicate predicateWithFormat

How to get iOS appStoreReceiptURL into Base 64 Encoded String?

阅读更多关于 How to get iOS appStoreReceiptURL into Base 64 Encoded String?

问题 I want to use appStoreReceiptURL to see which version of the app someone purchased. How can I get this into a string? I'm testing this by downloading the app from the store, then running a new version of the app from Xcode. Here is what I've tried: NSURL *receiptUrl = [[NSBundle mainBundle] appStoreReceiptURL]; NSLog(@"receiptUrl %@",[receiptUrl path]); if ([[NSFileManager defaultManager] fileExistsAtPath:[receiptUrl path]]) { NSLog(@"exists"); NSError *error; NSString *receiptString = [

How to convert std::string to NSString?

阅读更多关于 How to convert std::string to NSString?

问题 Hi I am trying to convert a standard std::string into an NSString but I'm not having much luck. I can convert successfully from an NSString to a std::string with the following code NSString *realm = @"Hollywood"; std::string REALM = [realm cStringUsingEncoding:[NSString defaultCStringEncoding]]; However I get a compile time error when I try the following NSString *errorMessage = [NSString stringWithCString:REALM encoding:[NSString defaultCStringEncoding]]; The error I get is Cannot convert

iOS项目开发—文件下载功能的实现

阅读更多关于 iOS项目开发—文件下载功能的实现

一、简单说明 1.思路把下载的data追加到文件的尾部，直到所有的数据下载完为止。 1.在连通了服务器的时候，创建一个空的文件到沙盒中NSFileManager(文件管理类) 2.创建写数据的文件句柄 3.在接收到服务器返回的数据后，把data写入到创建的空文件中，但是不能使用writeTofile(会覆盖) 3.1移动到文件的尾部 3.2从当前移动的位置，写入数据 4.服务器的数据加载完毕后关闭连接，不再输入数据在文件中二、代码示例 1.代码：新建一个类，让其继承自NSObject类，一个文件下载器只下载一个文件。自定义类的TXFileDownloader.h代码： 1 // 2 // TXFileDownloader.h 3 // 文件下载 4 // 5 // Created by 鑫 on 14/12/23. 6 // Copyright (c) 2014年梁镋鑫. All rights reserved. 7 // 8 9 #import <Foundation/Foundation.h> 10 11 @interface TXFileDownloader : NSObject 12 //下载的远程url(连接到服务器的路径) 13 @property(nonatomic,strong)NSString *url; 14 //下载后的存储路径（文件下载到什么地方）

Number of Occurrences of a Character in NSString

阅读更多关于 Number of Occurrences of a Character in NSString

问题 I have an NSString or NSMutableString and would like to get the number of occurrences of a particular character. I need to do this for quite a few characters -- uppercase English characters in this case -- so it would be nice for it to be quick. 回答1: replaceOccurrencesOfString:withString:options:range: will return the number of characters replaced in a NSMutableString . [string replaceOccurrencesOfString:@"A" withString:@"B" options:NSLiteralSearch range:NSMakeRange(0, [receiver length])];