[iOS]使用UIActivityViewController实现AirDrop功能

AirDrop是iOS7中新增的一个近距离分享功能，两个相邻的iOS设备可以通过AirDrop实现传递图片、文件等功能，有了AirDrop基本上可抛弃类似Dropbox的ShareLink和PublicFolder功能。

iOS7的SDK中已经在UIActivityViewController中内置了AirDrop功能，使用时与分享到twitter和facebook的方式基本一致，只需要将需要传递的文件URL设置给UIActivityViewController对象的ActivityItems对象即可，区别在于：如果传递文件，那么URL应该是“file://”开头，而不是常见的“http://”开头

参考代码:

NSString *filePath = "Documents/aaa.png"
NSURL *url = [NSURL fileURLWithPath:filePath]; 
NSArray *items = [NSArray ArrayWithObjects:url,nil];
UIActivityViewController *activityViewController = 
  [[UIActivityViewController alloc] initWithActivityItems:items applicationActivities:nil];
[self presentViewController:activityViewController animated:YES completion:nil]; 

如果只想使用AirDrop而不使用其他分享功能，只需要设置UIActivityViewController的excludedActivityTypes属性即可。
以下是可以隐藏的对象

#6.0开始支持
UIKIT_EXTERN NSString *const UIActivityTypePostToFacebook     
UIKIT_EXTERN NSString *const UIActivityTypePostToTwitter      
UIKIT_EXTERN NSString *const UIActivityTypePostToWeibo        
UIKIT_EXTERN NSString *const UIActivityTypeMessage            
UIKIT_EXTERN NSString *const UIActivityTypeMail               
UIKIT_EXTERN NSString *const UIActivityTypePrint              
UIKIT_EXTERN NSString *const UIActivityTypeCopyToPasteboard   
UIKIT_EXTERN NSString *const UIActivityTypeAssignToContact    
UIKIT_EXTERN NSString *const UIActivityTypeSaveToCameraRoll   
#7.0以后新增
UIKIT_EXTERN NSString *const UIActivityTypeAddToReadingList   
UIKIT_EXTERN NSString *const UIActivityTypePostToFlickr       
UIKIT_EXTERN NSString *const UIActivityTypePostToVimeo        
UIKIT_EXTERN NSString *const UIActivityTypePostToTencentWeibo 
UIKIT_EXTERN NSString *const UIActivityTypeAirDrop            

具体用法如下，这里只保留AirDrop：

NSArray *excludedActivities = @[UIActivityTypePostToFacebook, 
								UIActivityTypePostToTwitter,
								UIActivityTypePostToWeibo, 
								UIActivityTypeMessage, 
								UIActivityTypeMail, 
								UIActivityTypePrint,
								UIActivityTypeCopyToPasteboard, 
								UIActivityTypeAssignToContact, 
								UIActivityTypeSaveToCameraRoll, 
								UIActivityTypeAddToReadingList,
								UIActivityTypePostToFlickr, 
								UIActivityTypePostToVimeo, 
								UIActivityTypePostToTencentWeibo]; 
activityViewController.excludedActivityTypes = excludedActivities; 

完整的代码：

NSString *filePath = "Documents/aaa.png"
NSURL *url = [NSURL fileURLWithPath:filePath]; 
NSArray *items = [NSArray ArrayWithObjects:url,nil];
UIActivityViewController *activityViewController = 
  [[UIActivityViewController alloc] initWithActivityItems:items applicationActivities:nil]; 
NSArray *excludedActivities = @[UIActivityTypePostToFacebook, 
								UIActivityTypePostToTwitter,
								UIActivityTypePostToWeibo, 
								UIActivityTypeMessage, 
								UIActivityTypeMail, 
								UIActivityTypePrint,
								UIActivityTypeCopyToPasteboard, 
								UIActivityTypeAssignToContact, 
								UIActivityTypeSaveToCameraRoll, 
								UIActivityTypeAddToReadingList,
								UIActivityTypePostToFlickr, 
								UIActivityTypePostToVimeo, 
								UIActivityTypePostToTencentWeibo]; 
activityViewController.excludedActivityTypes = excludedActivities; 
[self presentViewController:activityViewController animated:YES completion:nil]; 

关于文件路径URL，一般APP的用户数据都在APP的Documents目录下，使用”Documents/aaa.png”的方式即可取得
如果需要使用Bundle路径下的文件可以使用以下方式

NSString *fileName=@"aaa.png"
NSArray *fileComponents = [filename componentsSeparatedByString:@"."]; 
NSString *filePath = nil;
if([fileComponents count] == 0) {
}else if([fileComponents count] == 1) {
	filePath = [[NSBundle mainBundle] pathForResource:[fileComponents objectAtIndex:0] 
	                                           ofType:nil]; 
}else if([fileComponents count] == 2) {
	filePath = [[NSBundle mainBundle] pathForResource:[fileComponents objectAtIndex:0] 
	                                           ofType:[fileComponents objectAtIndex:1]]; 
}
NSURL *url = [NSURL fileURLWithPath:filePath];