vb.net print barcode labels Class NSFileHandle in Objective-C

Creator Quick Response Code in Objective-C Class NSFileHandle

Table 8.4
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Ways to manipulate files using the SDK Method fileHandleForReadingAtPath: fileHandleForWritingAtPath: fileHandleForUpdatingAtPath: readDataOfLength: Summary Class methods that allow you to open a file
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Class NSFileHandle
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NSFileHandle
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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
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NSFileHandle
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readDataToEndOfFile
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NSFileHandle NSFileManager
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closeFile contentsAtPath:
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NSData
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initWithContentsOfFile:
NSData
writeToFile:atomically:
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Opening files
Table 8.4 Ways to manipulate files using the SDK (continued) Method stringWithContentsOfFile:encoding:error: Summary Class method that returns an NSString with the complete file s contents
Class NSString
NSString
initWithData:encoding:
Returns an NSString with the NSData s contents Writes the NSString to a file
NSString
writeToFile:atomically:encoding:error:
As table 8.4 shows, you can access files in a huge variety of ways after 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 can 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 will 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 need only a single line of code:
NSString *myContents = [NSString stringWithContentsOfFile:myFile encoding:NSASCIIStringEncoding error:&error];
Table 8.4 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 approFile content priate class reference for additional details. In this section and in our next When you re working with files, you re example we re largely assuming that files contain plain, likely to be doing one of two things. Either unstructured text. But this you have files that contain large blobs of user doesn t have to be the case. information, or you have files that contain XML is a great way to store local short snippets of data that you ve saved for data in a more structured format. your program. To demonstrate how to use a 14 covers how to read XML and includes an example of few of the file objects and methods, you ll reading local XML data. tackle the first problem by building a simple notepad prototype.
Filesaver: a UITextView example
This program lets you maintain a text view full of information from one session to another. It s relatively basic, but you can imagine how you could expand it to mimic the Notepad program, with its multiple notes, toolbars, navigator, and image background.
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Data: actions, preferences, and files
Listing 8.4 shows this simple filesaver example. The objects, as usual, were created in Interface Builder: a UIToolBar (with associated UIBarButtonItem) and a UITextView.
Listing 8.4 A prototype notepad program that maintains a text field as a file
@implementation filesaverViewController - (void)viewDidLoad { NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; Creates file path filePath = [documentsDirectory stringByAppendingPathComponent: @"textviewcontent"]; [filePath retain]; NSFileManager *myFM = [NSFileManager defaultManager]; if ([myFM isReadableFileAtPath:filePath]) { myText.text = [NSString stringWithContentsOfFile:filePath encoding:NSASCIIStringEncoding error:nil]; } keyboardIsActive = NO; [super viewDidLoad]; } Executes Done action -(IBAction)finishEditing:(id)sender { if (keyboardIsActive == YES) { [myText resignFirstResponder]; } - (void)textViewDidBeginEditing: (UITextView *)textView { if ([myText.text compare:@"Type Text Here."] == NSOrderedSame) { myText.text = [NSString string]; } keyboardIsActive = YES; } - (void)textViewDidEndEditing:(UITextView *)textView { [textView.text writeToFile:filePath atomically:YES encoding:NSASCIIStringEncoding error:NULL]; keyboardIsActive = NO; } ... @end
This program shows how easy it is to access files. The hardest part is determining the path for the file, but that involves using the path-creation methods we looked at a few sections back. When you have your path, you save it as a variable so that you won t have to re-create the path later B. Next, you use NSFileManager to determine whether a file exists. If it does, you can immediately fill your UITextField with its content. Finally, you set a keyboardIsActive variable, which you update throughout the program.
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