iOS開發中，獲取圖片之后保存或下載到本地相冊中

#pragma mark 先獲取本地圖片或者網絡圖片
- (void)saveHeaderImageWith:(NSString *)path
{
    UIImage *img = [UIImage imageWithContentsOfFile:path];
    //這里img也可以是從網絡獲取的圖片
    [self saveImageToPhotos:img];
}

#pragma mark 保存圖片
- (void)saveImageToPhotos:(UIImage*)savedImage
{
    UIImageWriteToSavedPhotosAlbum(savedImage, self, @selector(image:didFinishSavingWithError:contextInfo:), NULL);
}

#pragma mark 系統的完成保存圖片的方法
- (void)image: (UIImage *) image didFinishSavingWithError: (NSError *) error contextInfo: (void *) contextInfo
{
    NSString *msg = nil ;
    if (error != NULL) {
        msg = @"保存圖片失敗" ;
    } else {
        msg = @"保存圖片成功" ;
    }
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"保存圖片結果提示" message:msg delegate:self cancelButtonTitle:@"確定" otherButtonTitles:nil];
    [alert show];
}