- (NSString *)dataPath:(NSString *)file 
{ 
    NSString *path = [[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:@"badge"]; 
    BOOL bo = [[NSFileManager defaultManager] createDirectoryAtPath:path withIntermediateDirectories:YES attributes:nil error:nil]; 
    NSAssert(bo,@"创建目录失败"); 
    NSString *result = [path stringByAppendingPathComponent:file]; 
    return result; 
}  
- (void)viewDidLoad 
{ 
    [super viewDidLoad];  
    //此处首先指定了图片存取路径（默认写到应用程序沙盒 中） 
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES); 
    //并给文件起个文件名 
    NSString *imageDir = [[[paths objectAtIndex:0] stringByAppendingPathComponent:@"163"] stringByAppendingPathComponent:@"songzi"]; 
    //存放图片的文件夹 
    NSString *imagePath =[imageDir stringByAppendingPathComponent:@"文件名.png"]; 
    NSData *data = nil; 
    //检查图片是否已经保存到本地 
    if([self isExistsFile:imagePath]){ 
        data=[NSData dataWithContentsOfFile:imagePath]; 
    }else{ 
        data = [NSData dataWithContentsOfURL:[NSURL URLWithString: @"网址"]]; 
        //创建文件夹路径 
        [[NSFileManager defaultManager] createDirectoryAtPath:imageDir withIntermediateDirectories:YES attributes:nil error:nil]; 
        //创建图片 
        [UIImagePNGRepresentation([UIImage imageWithData:data]) writeToFile:imagePath atomically:YES];          
    } 
    imageView.image = [UIImage imageWithData:data]; 
} 

NSString *path = [[NSBundle mainBundle] pathForResource:fileName ofType:@""];
if(path==NULL)

NSFileManager *fileManager = [NSFileManager defaultManager];
   //Get documents directory
   NSArray *directoryPaths = NSSearchPathForDirectoriesInDomains
   (NSDocumentDirectory, NSUserDomainMask, YES);
   NSString *documentsDirectoryPath = [directoryPaths objectAtIndex:0];
   if ([fileManager fileExistsAtPath:@""]==YES) {
        NSLog(@"File exists");
    }  

//判断文件是否存在
    if(![c judgeFileExist:@"user.plist"])      
    {
        NSLog(@"请确认该文件是否存在！");
        return;
    }

//判断文件是否存在
-(BOOL)judgeFileExist:(NSString * )fileName
{
    //获取文件路径
    NSString *path = [[NSBundle mainBundle] pathForResource:fileName ofType:@""];
    if(path==NULL)
        return NO;
    returnYES;
}