监视相册变化

AssetSource.m

//
//  AssetSource.m
//  CameraWathcher
//
//  Created by FengXing on 13-9-9.
//  Copyright (c) 2013年 FengXing. All rights reserved.
//

#import "AssetSource.h"

@interface AssetSource ()
@property ALAssetsLibrary *assetsLibrary;
@property NSMutableArray *assetsArray;
@property NSInteger assetCount;
@end

@implementation AssetSource

+ (id)sharedInstance
{
    static AssetSource *ins = nil;
    if (ins == nil) {
        ins = [[AssetSource alloc] init];
        ins.assetsArray = [[NSMutableArray alloc] init];
        ins.maxTimeInterval = 30;
    }
    return ins;
}

- (void)watch
{
    self.assetsLibrary = [[ALAssetsLibrary alloc] init];
    ALAssetsLibrary *notificationSender = nil;
	
	NSString *minimumSystemVersion = @"4.1";
	NSString *systemVersion = [[UIDevice currentDevice] systemVersion];
	if ([systemVersion compare:minimumSystemVersion options:NSNumericSearch] != NSOrderedAscending)
		notificationSender = self.assetsLibrary;
	
	[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(assetsLibraryDidChange:)
												 name:ALAssetsLibraryChangedNotification object:notificationSender];
    
    double delayInSeconds = 2.0;
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
        [self assetsLibraryDidChange:nil];
    });
}

- (void)unwatch
{
    if (self.assetsLibrary) {
		[[NSNotificationCenter defaultCenter] removeObserver:self name:ALAssetsLibraryChangedNotification object:nil];
#if !__has_feature(objc_arc)
		[self.assetsLibrary release];
#endif
	}
}

- (void)assetsLibraryDidChange:(NSNotification *)notify
{
    ALAssetsLibrary *assetLibrary = self.assetsLibrary;
	[assetLibrary enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos
                                usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
                                    if (group) {
                                        *stop = YES;
                                        [group setAssetsFilter:[ALAssetsFilter allPhotos]];
                                        if ([group numberOfAssets] <= self.assetCount) {
                                            return;
                                        } else {
                                            self.assetCount = [group numberOfAssets];
                                        }
                                        [group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:self.assetCount-1]
                                                               options:0
                                                             usingBlock:
                                         ^(ALAsset *asset, NSUInteger index, BOOL *stopIt) {
                                             if (asset) {
                                                 self.lastAsset = asset;
                                                 *stopIt = YES;
                                                 if ([self isTakenInTime:self.lastAsset]) {
                                                     [[NSNotificationCenter defaultCenter] postNotificationName:kAssetSourceLastTake object:self];
                                                 }
                                             }
                                         }];
                                    }
                                }
                              failureBlock:^(NSError *error) {
                                  NSLog(@"error enumerating AssetLibrary groups %@\n", error);
                              }];
}

- (BOOL)isTakenInTime:(ALAsset *)asset
{
    NSDate *date = [asset valueForProperty:ALAssetPropertyDate];
    if (date == nil) {
        return NO;
    }
    return -[date timeIntervalSinceNow] < self.maxTimeInterval;
}
@end