Block实战之UIActionSheet

Block是ios 4的新东西，有了它，源码的逻辑将更清楚，代码的可读性将提高。熟悉函数指针的朋友对Block不会感冒的，因为它们实质是一样的，只是叫清一不样。今天将实战BLOCK，我们将封装一个支持Block的UIActionSheet。好了废话少说，直接上代码：

PLActionSheet.h

#import <UIKit/UIKit.h>

/**
 * A simple block-enabled API wrapper on top of UIActionSheet.
 */
@interface PLActionSheet : NSObject <UIActionSheetDelegate> {
@private
    UIActionSheet *_sheet;
    NSMutableArray *_blocks;
}

- (id) initWithTitle: (NSString *) title;

- (void) setCancelButtonWithTitle: (NSString *) title block: (void (^)()) block;
- (void) addButtonWithTitle: (NSString *) title block: (void (^)()) block;

- (void) showInView: (UIView *) view;

@end

PLActionSheet.m

#import "PLActionSheet.h"


@implementation PLActionSheet

- (id) initWithTitle: (NSString *) title {
    if ((self = [super init]) == nil)
        return nil;
    
    /* Initialize the sheet */
    _sheet = [[UIActionSheet alloc] initWithTitle: title delegate: self cancelButtonTitle: nil destructiveButtonTitle: nil otherButtonTitles: nil];

    /* Initialize button -> block array */
    _blocks = [[NSMutableArray alloc] init];

    return self;
}

- (void) dealloc {
    _sheet.delegate = nil;
    [_sheet release];

    [_blocks release];

    [super dealloc];
}


- (void) setCancelButtonWithTitle: (NSString *) title block: (void (^)()) block {
    [self addButtonWithTitle: title block: block];
    _sheet.cancelButtonIndex = _sheet.numberOfButtons - 1;
}

- (void) addButtonWithTitle: (NSString *) title block: (void (^)()) block {
    [_blocks addObject: [[block copy] autorelease]];
    [_sheet addButtonWithTitle: title];
}

- (void) showInView: (UIView *) view {
    [_sheet showInView: view];

    /* Ensure that the delegate (that's us) survives until the sheet is dismissed */
    [self retain];
}

- (void) actionSheet: (UIActionSheet *) actionSheet clickedButtonAtIndex: (NSInteger) buttonIndex {
    /* Run the button's block */
    if (buttonIndex >= 0 && buttonIndex < [_blocks count]) {
        void (^b)() = [_blocks objectAtIndex: buttonIndex];
        b();
    }

    /* Sheet to be dismissed, drop our self reference */
    [self release];
}

@end

用法如下：

- (void) displaySheet {
    PLActionSheet *sheet = [[PLActionSheet alloc] initWithTitle: @"Destination"];
    
    /* A re-usable block that simply displays an alert message */
    void (^alert)(NSString *) = ^(NSString *message) {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle: @"Destination Selected"
                                                        message: message
                                                       delegate: nil
                                              cancelButtonTitle: @"OK"
                                              otherButtonTitles: nil];
        
        [alert show];
        [alert release];
    };
    
    [sheet addButtonWithTitle: @"Work" block: ^{
        alert(@"Work selected");
    }];
    
    [sheet addButtonWithTitle: @"Home" block: ^{
        alert(@"Home selected");
    }];
    
    [sheet addButtonWithTitle: @"School" block: ^{
        alert(@"School selected");
    }];
    
    [sheet setCancelButtonWithTitle: @"Cancel" block: ^{}];
 
    [sheet showInView: self.window];
    [sheet release];
}

采用BLOCK的方法，源码可读性大大增强。如果我们在同一个Controller里需要多个UIActionSheet, 而只有一个delegate方法，那在这个delegate方法里就要跟踪现在是哪一个UIActionSheet，这样就会有很多if else的代，也难于维护。以后将多采用BLOCK来写程序了。