1、ALAssetsLibraryAccessor单例

ALAssetsLibraryAccessor.h

#import <Foundation/Foundation.h>

@class ALAssetsLibrary;

@interface ALAssetsLibraryAccessor : NSObject {
    ALAssetsLibrary *assetsLibrary_;
}

+ (ALAssetsLibraryAccessor *)sharedInstance;

- (ALAssetsLibrary *)assetsLibrary;

- (void)refreshAssetsLibrary;

@end

ALAssetsLibraryAccessor.m

#import "ALAssetsLibraryAccessor.h"
#import <AssetsLibrary/AssetsLibrary.h>

@implementation ALAssetsLibraryAccessor

- (id)init {
    self = [super init];
    if (self) {
        assetsLibrary_ = [[ALAssetsLibrary alloc] init];
    }

    return  self;
}

+ (ALAssetsLibraryAccessor *)sharedInstance
{
    static ALAssetsLibraryAccessor *sharedInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedInstance = [[ALAssetsLibraryAccessor alloc] init];
    });
    return sharedInstance;
}

- (ALAssetsLibrary *)assetsLibrary {
    return assetsLibrary_;
}

- (void)refreshAssetsLibrary {
    assetsLibrary_ = nil;
    assetsLibrary_ = [[ALAssetsLibrary alloc] init];
}

@end

2、ALAssetHelper获取AlAsset图片

ALAssetHelper.h

#import <Foundation/Foundation.h>
#import <AssetsLibrary/AssetsLibrary.h>

@interface ALAssetHelper : NSObject

+ (UIImage *)getImage:(ALAsset *)asset original:(BOOL)original;

@end

ALAssetHelper.m

#import "ALAssetHelper.h"

@implementation ALAssetHelper

+ (UIImage *)getImage:(ALAsset *)asset original:(BOOL)original
{
    UIImage *image = nil;
    CGImageRef ref = nil;

    ALAssetRepresentation *rep = [asset defaultRepresentation];

    if (original) {
        // 获取ios剪裁后的图片
        NSData *xmpData = rep.metadata[@"AdjustmentXMP"];
        if (xmpData != nil) {
            ref   = [rep fullScreenImage];
            image = [UIImage imageWithCGImage:ref];
        } else {
            ref   = [rep fullResolutionImage];
            image = [UIImage imageWithCGImage:ref
                                    scale:[rep scale]
                              orientation:(UIImageOrientation)[rep orientation]];
        }
    } else {
        ref   = [rep fullScreenImage];
        image = [UIImage imageWithCGImage:ref];
    }

    return image;
}

@end

3、枚举相册

- (void)enumerateAssetsGroups {
    self.assetGroups = [NSMutableArray arrayWithCapacity:0];

    ALAssetsLibrary *library = [[ALAssetsLibraryAccessor sharedInstance] assetsLibrary];

    // Load Albums into assetGroups
    dispatch_async(dispatch_get_main_queue(), ^{
        @autoreleasepool {
            // Group enumerator Block
            void (^assetGroupEnumerator)(ALAssetsGroup *, BOOL *) = ^(ALAssetsGroup *group, BOOL *stop)
            {
                if (group) {
                    [self.assetGroups addObject:group];
                } else {
                    // group is nil, so there are no more groups to enumerate
                }
            };

            // Group Enumerator Failure Block
            void (^assetGroupEnumberatorFailure)(NSError *) = ^(NSError *error) {
                if (error.code == ALAssetsLibraryAccessUserDeniedError ||
                error.code == ALAssetsLibraryAccessGloballyDeniedError) {
                // Denied Error
                }
            };

            // Enumerate Albums
            [library enumerateGroupsWithTypes:ALAssetsGroupAll
                               usingBlock:assetGroupEnumerator
                             failureBlock:assetGroupEnumberatorFailure];
        }
    });
}

4、枚举相片

- (void)enumerateAssets:(ALAssetsGroup *)assetGroup {
    NSMutableArray *assets = [NSMutableArray arrayWithCapacity:0];

    ALAssetsGroupEnumerationResultsBlock groupEnumeration = ^(ALAsset *result, NSUInteger index, BOOL *stop) {
        if (result) {
            [assets addObject:result];
        } else {
            //
        }
    };

    [assetGroup enumerateAssetsUsingBlock:groupEnumeration];
}

枚举相片的三个方法：

// These methods are used to retrieve the assets that match the filter.  
// The caller can specify which results are returned using an NSIndexSet. The index set's count or lastIndex cannot exceed -numberOfAssets.
// 'enumerationBlock' is used to pass back results to the caller and provide the opportunity to stop the filter.
// When the enumeration is done, 'enumerationBlock' will be called with result set to nil and index set to NSNotFound.
// If the application has not been granted access to the data, 'enumerationBlock' will be called with result set to nil, index set to NSNotFound, and stop set to YES.

- (void)enumerateAssetsUsingBlock:(ALAssetsGroupEnumerationResultsBlock)enumerationBlock;
- (void)enumerateAssetsWithOptions:(NSEnumerationOptions)options usingBlock:(ALAssetsGroupEnumerationResultsBlock)enumerationBlock;
- (void)enumerateAssetsAtIndexes:(NSIndexSet *)indexSet options:(NSEnumerationOptions)options usingBlock:(ALAssetsGroupEnumerationResultsBlock)enumerationBlock;

提问：

如何发送一个ALAsset对象的视频？