ios协议和委托

在iPhone开发协议和委托是常接触到的东西，到底什么是协议什么是委托，他们什么关系？

一 协议

(1)协议相当于没有与类相关联的接口，他申明一组方法，列出他的参数和返回值，共享给其他类使用，然后不进行实现，让用它的类来实现这些方法

(2)在任何一个类中，只有声明了协议，都可以实现协议里的方法。

(3)协议不是一个类，更没有父类了。

(3)协议里面的方法经常都是一些委托方法，

二 委托

委托，故名思议就是托别人办事。打个比方：

张三迫切需要一分工作，但是不知道去哪找。于是他就拜托（委托）李四给帮找一份合适工作，但是托人办事得给被人好处啊，于是张三给李四塞了一个红包（协议），于是李四通过自己关系在某公司找了一份文秘的工作(实现协议里面委托方法)，于然后他把文秘这份工作给了张三，张三就找到工作了；

三 我们来看一个比较常用的表格单元实现委托和协议

UITableViewDataSource协议和他的委托方法

@protocol UITableViewDataSource<NSObject>

@required

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section;

// Row display. Implementers should *always* try to reuse cells by setting each cell's reuseIdentifier and querying for available reusable cells with dequeueReusableCellWithIdentifier:
// Cell gets various attributes set automatically based on table (separators) and data source (accessory views, editing controls)

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath;

@optional

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView;              // Default is 1 if not implemented

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section;    // fixed font style. use custom view (UILabel) if you want something different
- (NSString *)tableView:(UITableView *)tableView titleForFooterInSection:(NSInteger)section;

// Editing

// Individual rows can opt out of having the -editing property set for them. If not implemented, all rows are assumed to be editable.
- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath;

// Moving/reordering

// Allows the reorder accessory view to optionally be shown for a particular row. By default, the reorder control will be shown only if the datasource implements -tableView:moveRowAtIndexPath:toIndexPath:
- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath;

// Index

- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView;                                                    // return list of section titles to display in section index view (e.g. "ABCD...Z#")
- (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index;  // tell table which section corresponds to section title/index (e.g. "B",1))

// Data manipulation - insert and delete support

// After a row has the minus or plus button invoked (based on the UITableViewCellEditingStyle for the cell), the dataSource must commit the change
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath;

// Data manipulation - reorder / moving support

- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath;

@end

这是一个完整协议定义

@protocol  协议名

声明方法

@end

但是我们还看到两个特殊关键字 @required  和 @optional

@required 表示我们用到这个协议的时候必须实现这个协议的方法

@optional 表示我们可选择性实现这些方法，看那个需要我们就去实现，不需要的就不实现

UITableViewDelegate协议和委托方法

@protocol UITableViewDelegate<NSObject, UIScrollViewDelegate>

@optional

// Display customization

- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath;

// Variable height support

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath;
- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section;
- (CGFloat)tableView:(UITableView *)tableView heightForFooterInSection:(NSInteger)section;

// Section header & footer information. Views are preferred over title should you decide to provide both

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section;   // custom view for header. will be adjusted to default or specified header height
- (UIView *)tableView:(UITableView *)tableView viewForFooterInSection:(NSInteger)section;   // custom view for footer. will be adjusted to default or specified footer height

// Accessories (disclosures). 

- (UITableViewCellAccessoryType)tableView:(UITableView *)tableView accessoryTypeForRowWithIndexPath:(NSIndexPath *)indexPath __OSX_AVAILABLE_BUT_DEPRECATED(__MAC_NA,__MAC_NA,__IPHONE_2_0,__IPHONE_3_0);
- (void)tableView:(UITableView *)tableView accessoryButtonTappedForRowWithIndexPath:(NSIndexPath *)indexPath;

// Selection

// Called before the user changes the selection. Return a new indexPath, or nil, to change the proposed selection.
- (NSIndexPath *)tableView:(UITableView *)tableView willSelectRowAtIndexPath:(NSIndexPath *)indexPath;
- (NSIndexPath *)tableView:(UITableView *)tableView willDeselectRowAtIndexPath:(NSIndexPath *)indexPath __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_3_0);
// Called after the user changes the selection.
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath;
- (void)tableView:(UITableView *)tableView didDeselectRowAtIndexPath:(NSIndexPath *)indexPath __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_3_0);

// Editing

// Allows customization of the editingStyle for a particular cell located at 'indexPath'. If not implemented, all editable cells will have UITableViewCellEditingStyleDelete set for them when the table has editing property set to YES.
- (UITableViewCellEditingStyle)tableView:(UITableView *)tableView editingStyleForRowAtIndexPath:(NSIndexPath *)indexPath;
- (NSString *)tableView:(UITableView *)tableView titleForDeleteConfirmationButtonForRowAtIndexPath:(NSIndexPath *)indexPath __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_3_0);

// Controls whether the background is indented while editing.  If not implemented, the default is YES.  This is unrelated to the indentation level below.  This method only applies to grouped style table views.
- (BOOL)tableView:(UITableView *)tableView shouldIndentWhileEditingRowAtIndexPath:(NSIndexPath *)indexPath;

// The willBegin/didEnd methods are called whenever the 'editing' property is automatically changed by the table (allowing insert/delete/move). This is done by a swipe activating a single row
- (void)tableView:(UITableView*)tableView willBeginEditingRowAtIndexPath:(NSIndexPath *)indexPath;
- (void)tableView:(UITableView*)tableView didEndEditingRowAtIndexPath:(NSIndexPath *)indexPath;

// Moving/reordering

// Allows customization of the target row for a particular row as it is being moved/reordered
- (NSIndexPath *)tableView:(UITableView *)tableView targetIndexPathForMoveFromRowAtIndexPath:(NSIndexPath *)sourceIndexPath toProposedIndexPath:(NSIndexPath *)proposedDestinationIndexPath;               

// Indentation

- (NSInteger)tableView:(UITableView *)tableView indentationLevelForRowAtIndexPath:(NSIndexPath *)indexPath; // return 'depth' of row for hierarchies

// Copy/Paste.  All three methods must be implemented by the delegate.

- (BOOL)tableView:(UITableView *)tableView shouldShowMenuForRowAtIndexPath:(NSIndexPath *)indexPath __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_5_0);
- (BOOL)tableView:(UITableView *)tableView canPerformAction:(SEL)action forRowAtIndexPath:(NSIndexPath *)indexPath withSender:(id)sender __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_5_0);
- (void)tableView:(UITableView *)tableView performAction:(SEL)action forRowAtIndexPath:(NSIndexPath *)indexPath withSender:(id)sender __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_5_0);

@end

在用的时候，我们现在声明协议

#import <UIKit/UIKit.h>

@interface BIDViewController : UIViewController <UITableViewDataSource, UITableViewDelegate>

@property (strong, nonatomic) NSDictionary *names;
@property (strong, nonatomic) NSArray *keys;
@end

实现UITableViewDataSource  UITableViewDelegate协议里面的委托方法

#pragma mark -
#pragma mark Table View Data Source Methods
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return [keys count];
}

- (NSInteger)tableView:(UITableView *)tableView
 numberOfRowsInSection:(NSInteger)section {
    NSString *key = [keys objectAtIndex:section];
    NSArray *nameSection = [names objectForKey:key];
    return [nameSection count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView
         cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSUInteger section = [indexPath section];
    NSUInteger row = [indexPath row];
    
    NSString *key = [keys objectAtIndex:section];
    NSArray *nameSection = [names objectForKey:key];
    
    static NSString *SectionsTableIdentifier = @"SectionsTableIdentifier";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:
                             SectionsTableIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc]
                 initWithStyle:UITableViewCellStyleDefault
                 reuseIdentifier:SectionsTableIdentifier];
    }
    
    cell.textLabel.text = [nameSection objectAtIndex:row];
    return cell;
}

- (NSString *)tableView:(UITableView *)tableView
titleForHeaderInSection:(NSInteger)section {
    NSString *key = [keys objectAtIndex:section];
    return key;
}

- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView {
    return keys;
}

这就就是实现一些里面的委托方法过程运行改程序运行结果

  

该程序源码http://download.csdn.net/detail/duxinfeng2010/4695666