MFMailComposeViewController：附加照片库中的图像

Question

我在将照片库中的图片附加到电子邮件时遇到了一些问题。

基本上，我的应用程序的一项功能允许用户拍照。当他们拍摄照片时，我会在 Core Data 中记录对图像的 URL 引用。我知道您必须通过ALAssetRepresentation 才能获得图像。当用户想要查看他们拍摄的图像时，我在我的应用程序中启动并运行了它。

我现在正尝试允许用户将所有为活动拍摄的照片附加到电子邮件中。在执行此操作时，我遍历存储 URL 引用的核心数据实体，调用从 ALAssetsLibrary 返回 UIImage 的方法，然后使用 NSData/UIImageJPEGRepresentation 和 MFMailComposeViewController/@ 附加它987654327@ 方法。

问题是：当邮件呈现给用户时，有代表图片的蓝色小方块，图片没有附上。

代码如下：

- (void)sendReportReport
{

    if ([MFMailComposeViewController canSendMail])
    {

        MFMailComposeViewController *mailer = [[MFMailComposeViewController alloc] init];

        mailer.mailComposeDelegate = self;

        [mailer setSubject:@"Log: Report"];

        NSArray *toRecipients = [NSArray arrayWithObjects:@"someone@someco.com", nil];
        [mailer setToRecipients:toRecipients];


        NSError *error;

        NSFetchRequest *fetchPhotos = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity = [NSEntityDescription 
                                       entityForName:@"Photo" inManagedObjectContext:__managedObjectContext];
        [fetchPhotos setEntity:entity];
        NSArray *fetchedPhotos = [__managedObjectContext executeFetchRequest:fetchPhotos error:&error];
        int counter;

        for (NSManagedObject *managedObject in fetchedPhotos ) {
            Photo *photo = (Photo *)managedObject;

//            UIImage *myImage = [UIImage imageNamed:[NSString stringWithFormat:@"%@.png", counter++]];
            NSData *imageData = UIImageJPEGRepresentation([self getImage:photo.referenceURL], 0.5);
//            NSData *imageData = UIImagePNGRepresentation([self getImage:photo.referenceURL]);
//            [mailer addAttachmentData:imageData mimeType:@"image/jpeg" fileName:[NSString stringWithFormat:@"%i", counter]];  
            [mailer addAttachmentData:imageData mimeType:@"image/jpeg" fileName:[NSString stringWithFormat:@"a.jpg"]];  

            counter++;

        }


        NSString *emailBody = [self getEmailBody];

        [mailer setMessageBody:emailBody isHTML:NO];

        [self presentModalViewController:mailer animated:YES];

    }
    else
    {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Failure"
                                                        message:@"Your device doesn't support the composer sheet"
                                                       delegate:nil
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:nil];
        [alert show];

    }

}

以及返回UIImage的方法：

#pragma mark - Get Photo from Asset Library
+ (ALAssetsLibrary *)defaultAssetsLibrary {
    static dispatch_once_t pred = 0;
    static ALAssetsLibrary *library = nil;
    dispatch_once(&pred, ^{
        library = [[ALAssetsLibrary alloc] init];
    });
    return library; 
}

- (UIImage *)getImage:(NSString *)URLReference
{

    __block UIImage *xPhoto = nil;

    ALAssetsLibraryAssetForURLResultBlock resultblock = ^(ALAsset *myasset)
    {
        UIImage *xImage;

        // get the image
        ALAssetRepresentation *rep = [myasset defaultRepresentation];
        CGImageRef iref = [rep fullScreenImage];

        if (iref) {
            xImage = [UIImage imageWithCGImage:iref];
        }

        xPhoto = xImage;

    };


    ALAssetsLibraryAccessFailureBlock failureblock  = ^(NSError *myerror)
    {
        NSLog(@"Error fetching photo: %@",[myerror localizedDescription]);
    };


    NSURL *asseturl = [NSURL URLWithString:URLReference];

    // create library and set callbacks
    ALAssetsLibrary *al = [DetailsViewController defaultAssetsLibrary];
    [al assetForURL:asseturl 
        resultBlock:resultblock
       failureBlock:failureblock];   

    return xPhoto;

}

注意：上面的代码确实可以运行，它只是不附加图像。另外，请注意，只要我已经将它们设置为UIImageView.Image，我就能够成功地在我的应用程序中附加来自图库的图像（基本上，我正在从UIImageView 中获取指向图像的指针和将它传递给addAttachmentData 方法。）只是当我尝试遍历核心数据并附加而没有先将图像设置为UIImageView 时，我遇到了麻烦。

任何提示将不胜感激！

谢谢！ 杰森

Answer 1

哦，现在我明白了.. sry。您正在使用异步块从资产库中获取图像。但在开始该操作后，您将返回xImage。但异步操作将在稍后完成。所以你返回 nil。

你需要像这样改变你的架构师：

在您的 .h 文件中，您需要两个新成员：

NSMutableArray* mArrayForImages;
NSInteger mUnfinishedRequests;

在你的 .m 文件中这样做：

- (void)sendReportReport
{
    // save image count
    mUnfinishedRequests = [fetchedPhotos count];

    // get fetchedPhotos
    [...]

    // first step: load images
    for (NSManagedObject *managedObject in fetchedPhotos )
    {
        [self loadImage:photo.referenceURL];    
    }
}

将您的 getImage 方法更改为 loadImage：

- (void)loadImage:(NSString *)URLReference
{
    NSURL *asseturl = [NSURL URLWithString:URLReference];

    ALAssetsLibraryAssetForURLResultBlock resultblock = ^(ALAsset *myasset)
    {    
        // get the image
        ALAssetRepresentation *rep = [myasset defaultRepresentation];
        CGImageRef iref = [rep fullScreenImage];

        if (iref) {
            [mArrayForImages addObject: [UIImage imageWithCGImage:iref]];
        } else {
            // handle error
        }

        [self performSelectorOnMainThread: @selector(imageRequestFinished)];
    };

    ALAssetsLibraryAccessFailureBlock failureblock  = ^(NSError *myerror)
    {
        NSLog(@"Error fetching photo: %@",[myerror localizedDescription]);

        [self performSelectorOnMainThread: @selector(imageRequestFinished)];
    };


    // create library and set callbacks
    ALAssetsLibrary *al = [DetailsViewController defaultAssetsLibrary];
    [al assetForURL:asseturl 
        resultBlock:resultblock
       failureBlock:failureblock];
}

创建一个新的回调方法：

- (void) imageRequestFinished
{
    mUnfinishedRequests--;
    if(mUnfinishedRequests <= 0)
    {
       [self sendMail];
    }
}

还有一个额外的方法，在获取图片后最终发送邮件：

- (void) sendMail
{
    // crate mailcomposer etc
    [...]

    // attach images
    for (UIImage *photo in mArrayForImages )
    {
                NSData *imageData = UIImageJPEGRepresentation(photo, 0.5);
                [mailer addAttachmentData:imageData mimeType:@"image/jpeg" fileName:[NSString stringWithFormat:@"a.jpg"]];
    }

    // send mail
    [...]
}