Cocoa programming in Objective-C

Creation QR Code ISO/IEC18004 in Objective-C Cocoa programming

class uses the dictionary to store each command-line parameter and, if necessary, its corresponding value. The WGetParameters class initializes its data members through its init method. The init method, like a C++ constructor, is called when the class is instantiated by the runtime system and is typically used for initializing the class s data members. Rather than setting the hash table values within the init method, you send a message to initToDefaults and have it set the values to their defaults. You do this so the program can reuse the method to respond to the user selecting the Reset button, which also sets the model to its default values. In addition to the dictionary, the class contains an NSMutableString data member, which holds the command-line version of the current state of the model. Let s look at the most important class methods:

getValue and setValue Enable controlled access to the class and therefore the model. The getValue method takes a key parameter that it uses to look up and return the associated value in the model. The setValue method takes two parameters (a key and value) that the class uses to set the value for the associated key. getData Responsible for taking the current model state and returning an array of each set key/value pair. By set, I mean a parameter selected by the user in the interface. For example, when the program starts, the data model is set to default values. When the user clicks the Download button, the program controllers query each view, update the model based on the state of the view, and send a getData message to the model, which it responds to by returning the selected command-line parameters. The formatCommandLine method uses the getData method to get the current parameters and convert them to a wget command-line representation. saveData and loadData Handle saving the current model to a file, loading a saved file, and populating the model with the stored values. These are two of the more interesting methods. The program uses them to handle this feature. The scenario feature enables the user to save the current setting to a file they can load later. As you can see from the following snippet, the saveData method is only one line this is all it takes to save the contents of an NSMutableDictionary to a file:

- (void)saveData:(NSString *)fname { [data writeToFile:fname atomically:YES]; } - (void)loadData:(NSString *)fname

{ NSString *s = fname; s = [s stringByExpandingTildeInPath]; [s retain]; [data release]; data = [[NSMutableDictionary alloc] initWithContentsOfFile:s]; if (data == nil) { data = [[NSMutableDictionary alloc] init]; [self initToDefaults]; } }

The first parameter is the name of the file. The second is a Boolean flag that tells the method how to save the data. If it is YES, the method saves the data to a temporary file and, if successful, copies that file over the named file. If NO, the method writes the data directly to the specified file without the temporary copy. (Temporary copies protect the user if the power is cut while the file is being written.) The format of the files is XML. Here s an edited example of the XML output:

< xml version="1.0" encoding="UTF-8" > <!DOCTYPE plist SYSTEM "file://localhost/System/Library/DTDs/ PropertyList.dtd"> <plist version="0.9"> <dict> <key>--accept=</key> <string></string> <key>--append-output=</key> <string></string> <key>--backup-converted</key> <string>0</string> <key>--base=</key> <string></string> <key>extra-commands</key> <string></string> <key>raw-command</key> <string></string> </string> </dict> </plist>

loadData Releases the current model and loads the data from the specified file into a new model. If there is an error (data == nil), the method sets the model to its default values. stringByExpandingTildeInPath Expands a path name that contains ~ (the user s home directory) to a full path name.