2d barcode generator c# free Accessing other directories in Objective-C

Generating QR Code in Objective-C Accessing other directories

16.3.2 Accessing other directories
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When working with directories other than the bundle, you have to think about two things: how to access those files and how to move files among multiple directories.
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RETRIEVING A FILE
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Once a file is sitting in your Documents directory, you can retrieve it much like you retrieved files from the bundle directory:
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NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; NSString *docPath = [documentsDirectory stringByAppendingPathComponent:dbFile];
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The magic here occurs in the NSSearchPathForDirectoriesInDomains function. The first argument is usually NSDocumentDirectory or NSLibraryDirectory, depending on which directory you want to get to. The other two arguments should always be the same for the iPhone. The result will be an array of strings, with each containing a path. The first path in the NSArray will usually be the right one, as shown here. You can then use the stringByAppendingPathComponent: method, like before, to build the complete path for your file. Voila! You ve now used some slightly different methods to access a file in your Documents directory rather than the bundle directory.
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COPYING A FILE
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There s been a slight disconnect in our discussion of files and directories to date. When you compile your project, all of your files will be placed into your application bundle. But if you ever want to edit a file, it must be placed in a different directory,
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Data: actions, preferences, files, SQLite, and addresses
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such as Documents. So how do you get a file from one place to the other You use the NSFileManager:
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NSFileManager *fileManager = [NSFileManager defaultManager]; success = [fileManager copyItemAtPath:bundlePath toPath:docPath error:&error];
The file manager is a class that allows you to easily manipulate files by creating them, moving them, deleting them, and otherwise modifying them. As is the case with many classes we ve seen, you initialize it by accessing a shared object. You can do lots of things with the file manager, including copying (as we ve done here) and checking for a file s existence (which we ll demonstrate shortly). You should look at the NSFileManager class reference for complete information. As we ll see, the NSFileManager is one of numerous classes that you can use to work with files.
16.3.3 Manipulating files
It s possible that once you ve built your file path, you ll be ready to immediately read the file s contents, using something like the UIImage methods (which we ll touch upon in chapter 19) or the functions related to SQLite (which we ll cover later in this chapter). But it s also possible that you ll want to manipulate the raw files, reading and parsing them in your code, as soon as you ve created a file path. There are numerous ways to do this, as shown in table 16.4.
Table 16.4 A couple of ways to manipulate files using the SDK Method Summary Allows you to open a file
Class
NSHandle
fileHandleForReadingAtPath: fileHandleForWritingAtPath: fileHandleForUpdatingAtPath: readsDataofLength:
NSHandle
Returns an NSData containing the specified number of bytes from the file Returns an NSData with the rest of the file s content Closes an NSHandle Returns an NSData with the complete file s contents Creates an NSData with the complete file s contents Writes the NSData to a file Returns an NSString with the complete file s contents
NSHandle NSHandle NSFileManager NSData NSData NSString
readsDataToEndOfFile closeFile contentsAtPath: initWithContentsOfFile: writeToFile:atomically: stringWithContentsOfFile:encoding:error:
Opening files
Table 16.4 A couple of ways to manipulate files using the SDK (continued) Method Summary
Class
NSString
initWithData:encoding:
Returns an NSString with the NSData s contents Writes the NSString to a file
NSString
writeToFile:atomically:encoding:error:
As table 16.4 shows, you can access files in a huge variety of ways once you ve created a file path. If you re a C programmer, opening a file handle, reading from that file handle, and finally closing that file handle is apt to be the most familiar approach. Or, you could use a shortcut and go straight to the NSFileManager and have it do the whole process. Even quicker is using methods from NSData or NSString to directly create an object of the appropriate type. Any of these simpler methods is going to cost you the ability to step through a file byte by byte, which may be a limitation or a benefit, depending on your program. But with the simpler methods, you just need a single line of code:
NSString *myContents = [NSString stringWithContentsOfFile:myFile encoding:NSASCIIStringEncoding error:&error];
Table 16.4 also lists a few ways to write back to files, including simple ways to dump an NSData object or an NSString object to a file. There are also other ways. When you decide which set of methods you re most comfortable using, you should consult the appropriate class reference for additional details.
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