MFMailComposeViewController：附加照片库中的图像

Question

将照片库中的图像附加到电子邮件时遇到麻烦。

基本上，我的应用程序的功能之一允许用户拍照。 当他们拍摄快照时，我在Core Data中记录了指向图像的URL参考。 我了解您必须通​​过ALAssetRepresentation才能获取图像。 当用户想要查看他们拍摄的图像时，我已经在我的应用程序中启动了该程序。

我现在正试图允许用户将为事件拍摄的所有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Core Data实体，调用从ALAssetsLibrary返回UIImage的方法，然后使用NSData / UIImageJPEGRepresentation和MFMailComposeViewController / addAttachmentData方法将其附加。

问题是：向用户显示电子邮件时，会有蓝色的小方块代表图像，而图像未附加。

这是代码：

- (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：上面的代码可以运行，只是不附加图像。 另外，请注意，只要我已经将它们设置到UIImageView .Image中，我就可以成功地将其图像附加到我的应用程序中（基本上，我是将指针从UIImageView传递到图像，并将其传递给addAttachmentData方法）。这只是当我尝试通过核心数据进行迭代并附加不首先将图像设置成UIImageView ，我有麻烦了。

任何提示将非常感谢！

谢谢！ 杰森

Answer 1

哦，现在我明白了。 您正在使用异步块从资产库获取图像。 但是在开始该操作后，您将返回xImage 。 但是异步操作将在稍后完成。 因此，您返回的是nil。

您需要像这样更改您的架构师：

在您的.h文件中，您需要两个新成员：

NSMutableArray* mArrayForImages;
NSInteger mUnfinishedRequests;

在您的.m文件中执行以下操作：

- (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];
    }
}

还有一种在获取图像后最终发送邮件的额外方法：

- (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
    [...]
}