[Study Notes-Objective-C] Objective-C-Basic tutorial 2nd chapter 1 category, objectivec tutorial

[Study Notes-Objective-C] Objective-C-Basic tutorial 2nd chapter 1 category, objectivec tutorial
12.1 create category

Category is a way to add a new method to an existing class.

For example, obtain the length of a string and store it in the NSDictionary dictionary.

• Do not use category:

      NSNumber *number;      number = [NSNumber numberWithUnsignedInt: [string length]];      // ... do something with number

• Usage type:

  • CATEGORY declaration:

@interface NSString (NumberConvenience)- (NSNumber *) lengthAsNumber; @end // NumberConvenience

Note::

-(NSNumber *) lengthAsNumber {unsigned int length = [self length]; return ([NSNumber numberWithUnsignedInt: length]); // send lengthAsNumber to the string, returns the NSNumber object of the string length} // lengthAsNumber

Test file:

NSMutableDictionary * dict; dict = [NSMutableDictionary dictionary]; [dict setObject: [@ "hello" lengthAsNumber] forKey: @ "hello"]; [dict setObject: [@ "iLikeFish" lengthAsNumber] forKey: @ "iLikeFish"]; [dict setObject: [@ "Once upon a time" lengthAsNumber] forKey: @ "Once upon a time"]; NSLog (@ "% @", dict); // output: "Key = key content"

Advantage: If you enter a string, send the lengthAsNumber to the string,NowNSNumber object that can return the length of the string

Note::
This category belongs to NSString, so any NSString object can respond to the lengthAsNumber message.

12.11 category defects: 12.12 category advantages: 12.2 class extension)

Class Extension: a special class without a name.

Features:

Example: create Things class Extension

• Original Things class:

@interface Things : NSObject@property (assign) NSInteger thing1;@property (readonly, assign) NSInteger thign2;

• Extended Things class:

// Obtain the Things class and extend it by adding private attributes and Methods @ interface Things () {NSInteger thing4; // Private} @ property (readwrite, assign) NSInteger thing2; // changed the read and write permissions. Only private methods can be accessed in this class. Only getter method @ property (assign) NSInteger thign3 is available in public interfaces; // Private

Note:

One feature of object-oriented programming is information hiding, which only needs to be presented by users, but not by others. We can put this category in the. m file, or in a private header file.

12.3 implement code with scattered categories

You can use classes to distribute large (with many methods) classes to multiple. m files.

The NSWindow class has hundreds of methods, but uses classification:

@ Interface NSWindow (NSKeyboardUI) // keyboard @ interface NSWindow (NSToolbarSupport) // toolbar @ interface NSWindow (NSDrag) // drag and drop function @ interface NSWindow (NSCarbonExtensions)

Note:

Cocoa designers place data functions in the Foundation framework by category, while plotting is in the Appkit framework.

12.4 create a Forward reference using a category (Forward References)

If you call a method without declaring the method, or are using a method that has not been released in another class, you need a category.

Specific Practices:

Declare in the public interface of the Car classrotateTiresMethod, declared in the categorymove
TireFromPosition:toPosition:To achieverotateTiresRotateTires can be used.

@intreface Car(Private)-(void)moveTireFromPosition:(int) pos1 toPosition: (int) pos2;@end // Private

Note:: Put in the respective @ implementation file

12.5 informal agreements and delegation types

Informal protocols are a type of NSObject that lists the methods that an object can respond. Informal protocols are used to implement Delegation

A delegate is an object that performs some work by another type of requests. Delegation is a technology that allows you to easily customize laid-off behaviors.

Example:
When a user clicks a row, before the tableView object is ready to be executed, it will ask whether the delegate object can select this row.

12.51 ITUnesFinder Project (omitted)

// New NSNetServiceBrowser object: NSNetServiceBrowser * browser; browser = [[NSNetServiceBrowser alloc] init]; // new ITunesFinder object ITunesFinder * finder; finder = [[ITunesFinder alloc] init]; // tells the net browser to use the ITunesFinder object as the proxy [browser setDelegate: finder]; // tells the browser to search for iTunes and share [browser searchForServicesOfType: @ "_ daap. _ tcp "inDomain: @" local. "];

12.52 delegation and category

Delegation is another type of application. An NSObject category can be sent to the delegate object.

@interface NSObject (NSNetServiceBrowserDelegateMethods)- (void) netServiceBrowserWillSearch:       (NSNetServiceBrowser *) browser;- (void) netServiceBrowserDidStopSearch:      (NSNetServiceBrowser *) browser;- (void) netServiceBrowser:      (NSNetServiceBrowser *) browser     didRemoveService: (NSNetService *) service     moreComing: (BOOL) moreComing;@end

By declaring it as a NSObject category, NSNetServiceBrowser can send one message to any object (as a proxy object)-informal Protocol

Note:: For informal agreements, you only declare what you want to declare.

12.53 response Selector

Selector: only a method name.

Specify selector:@selector();

Car classsetEngine:Method selector:@selector(setEngine:)

Car classsetTire:atIndex:Method selector:@selector(setTire:atIndex:)

Whether the query object can respond to a specific message

Car *car = [[Car alloc] init];if([Car respondsToSelector: @selector(setEngine:)]){    NSLog(@"Yes");}

Copyright Disclaimer: This article is an original article by the blogger and cannot be reproduced without the permission of the blogger.