UIAlertView中代表

Question

有人能如何委託解釋到UIAlertView作品？它是自動調用還是必須調用它？例如：

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex

Answer 1

只要你正確設置UIAlertView中的委託財產和執行協議，它會自動在用戶點擊您的警報按鈕調用。

看看「相關的示例代碼」中列出的項目在http://developer.apple.com/library/ios/#documentation/UIKit/Reference/UIAlertViewDelegate_Protocol/UIAlertViewDelegate/UIAlertViewDelegate.html看到它在行動。

Answer 2

委託的alertView:clickedButtonAtIndex:方法被自動通過UIAlertView調用。 UIAlertView的init方法將委託作爲參數之一。只要確保傳入響應alertView:clickedButtonAtIndex:的對象。

Answer 3

比方說，你顯示一個警告，其中的代表是「自我」

- (void)showAlert { 
     UIAlertView *myAlert = [[UIAlertView alloc] initWithTitle:@"My Alert" 
                 message:@"Do you want to continue?" 
        delegate:self 
        cancelButtonTitle:nil 
        otherButtonTitles:@"No", @"Yes", nil]; 
     [myAlert show]; 
     [myAlert release]; 
} 

爲了下面在.m文件的工作：

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex 

您的.h文件中需要在執行語句中引用UIAlertViewDelegate，如下所示：

@interface myViewController : UIViewController <UIAlertViewDelegate> { 
} 

這就是允許y我們的.m文件響應UIAlertViewDelegate方法調用。

Answer 4

這是一個委託包裝，以便您可以使用塊代替。執行流程將是相同的，但代碼的流程將更容易遵循。所以，用法：

[YUYesNoListener yesNoWithTitle:@"My Title" message:@"My Message" yesBlock:^ 
{ 
    NSLog(@"YES PRESSED!"); 
} 
noBlock:^ 
{ 
    NSLog(@"NO PRESSED!"); 
}]; 

...這裏是輔助類：

typedef void(^EmptyBlockType)(); 

@interface YUYesNoListener : NSObject <UIAlertViewDelegate> 

@property (nonatomic, retain) EmptyBlockType yesBlock; 
@property (nonatomic, retain) EmptyBlockType noBlock; 

+ (void) yesNoWithTitle:(NSString*)title message:(NSString*)message yesBlock:(EmptyBlockType)yesBlock noBlock:(EmptyBlockType)noBlock; 

@end 

@implementation YUYesNoListener 

@synthesize yesBlock = _yesBlock; 
@synthesize noBlock = _noBlock; 

- (id) initWithYesBlock:(EmptyBlockType)yesBlock noBlock:(EmptyBlockType)noBlock 
{ 
    self = [super init]; 
    if (self) 
    { 
     self.yesBlock = [[yesBlock copy] autorelease]; 
     self.noBlock = [[noBlock copy] autorelease]; 
    } 
    return self; 
} 

- (void) alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex 
{ 
    if (buttonIndex == 0 && self.noBlock) 
     self.noBlock(); 
    else if (buttonIndex == 1 && self.yesBlock) 
     self.yesBlock(); 

    [_yesBlock release]; 
    [_noBlock release]; 
    [alertView release]; 
    [self release]; 
} 

- (void) alertViewCancel:(UIAlertView *)alertView 
{ 
    if (self.noBlock) 
     self.noBlock(); 
    [_yesBlock release]; 
    [_noBlock release]; 
    [alertView release]; 
    [self release]; 
} 

+ (void) yesNoWithTitle:(NSString*)title message:(NSString*)message yesBlock:(EmptyBlockType)yesBlock noBlock:(EmptyBlockType)noBlock 
{ 
    YUYesNoListener* yesNoListener = [[YUYesNoListener alloc] initWithYesBlock:yesBlock noBlock:noBlock]; 
    [[[UIAlertView alloc] initWithTitle:title message:message delegate:yesNoListener cancelButtonTitle:@"No" otherButtonTitles:@"Yes", nil] show]; 
} 

@end