MFMailComposeViewController：附加照片庫中的圖像

Question

將照片庫中的圖像附加到電子郵件時遇到麻煩。

基本上，我的應用程序的功能之一允許用戶拍照。 當他們拍攝快照時，我在Core Data中記錄了指向圖像的URL參考。 我了解您必須通​​過ALAssetRepresentation才能獲取圖像。 當用戶想要查看他們拍攝的圖像時，我已經在我的應用程序中啟動了該程序。

我現在正試圖允許用戶將為事件拍攝的所有照片附加到電子郵件中。 在執行此操作時，我遍歷存儲URL引用的Core Data實體，調用從ALAssetsLibrary返回UIImage的方法，然后使用NSData / UIImageJPEGRepresentation和MFMailComposeViewController / addAttachmentData方法將其附加。

問題是：向用戶顯示電子郵件時，會有藍色的小方塊代表圖像，而圖像未附加。

這是代碼：

- (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：上面的代碼可以運行，只是不附加圖像。 另外，請注意，只要我已經將它們設置到UIImageView .Image中，我就可以成功地將其圖像附加到我的應用程序中（基本上，我是將指針從UIImageView傳遞到圖像，並將其傳遞給addAttachmentData方法）。這只是當我嘗試通過核心數據進行迭代並附加不首先將圖像設置成UIImageView ，我有麻煩了。

任何提示將非常感謝！

謝謝！ 傑森

Answer 1

哦，現在我明白了。 您正在使用異步塊從資產庫獲取圖像。 但是在開始該操作后，您將返回xImage 。 但是異步操作將在稍后完成。 因此，您返回的是nil。

您需要像這樣更改您的架構師：

在您的.h文件中，您需要兩個新成員：

NSMutableArray* mArrayForImages;
NSInteger mUnfinishedRequests;

在您的.m文件中執行以下操作：

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

    // get fetchedPhotos
    [...]

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

將您的getImage方法更改為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];
}

創建一個新的回調方法：

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

還有一種在獲取圖像后最終發送郵件的額外方法：

- (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
    [...]
}