ActivitySourceWrapper.h

typedef id (^ActivitySourceWrapperExecuteBlock)(UIActivityViewController* activityViewController,NSString* activityType);

@interface ActivitySourceWrapper : NSObject<UIActivityItemSource>

@property id placeholder;

-(id)initWithBlock:(ActivitySourceWrapperExecuteBlock)block;
-(id)initWithBlock:(ActivitySourceWrapperExecuteBlock)block withPlaceholder:(id)placeholder;

@end

ActivitySourceWrapper.m

@implementation ActivitySourceWrapper
{
    ActivitySourceWrapperExecuteBlock _block;
}


-(id)initWithBlock:(ActivitySourceWrapperExecuteBlock)block
{
    return [self initWithBlock:block withPlaceholder:nil];
}
-(id)initWithBlock:(ActivitySourceWrapperExecuteBlock)block withPlaceholder:(id)placeholder
{
    self = [super init];
    if(self) {
        _block = [block copy];
        if(placeholder) {
            self.placeholder = placeholder;
        }
    }
    return self;
}

-(id)activityViewController:(UIActivityViewController *)activityViewController itemForActivityType:(NSString *)activityType
{
    return _block(activityViewController,activityType);
}

-(id)activityViewControllerPlaceholderItem:(UIActivityViewController *)activityViewController
{
    if (self.placeholder) {
        return self.placeholder;
    }
    return @"";
}

@end

ActivitySourceWrapperTest.m

#import "ActivitySourceWrapper.h"

@implementation ActivitySourceWrapperTest

+(void)presentShareViewController:(UIViewController *)controller withText:(NSString *)text withUrl:(NSURL *)url
{
    id shareTextActivitySource =  [[ActivitySourceWrapper alloc] initWithBlock:^id(UIActivityViewController *activityViewController, NSString *activityType) {
        NSString *shareText = text;
        if([activityType isEqualToString:UIActivityTypePostToTwitter]) {
            shareText = [shareText stringByAppendingString:@" #ハッシュタグ"];
        }
        return shareText;
    }];

    id shareURLyActivitySource = [[ActivitySourceWrapper alloc] initWithBlock:^id(UIActivityViewController *activityViewController, NSString *activityType) {
        return url;
    }];

    NSArray *activitySourceArray = @[shareTextActivitySource, shareURLyActivitySource];
    UIActivityViewController *actViewCtr = [[UIActivityViewController alloc]initWithActivityItems:activitySourceArray applicationActivities:nil];

    [controller presentViewController:actViewCtr animated:YES completion:^{}];
}

@end