ios - 在图像尺寸缩小的同时显示 HUD

Question

我有一个应用程序，用户可以在其中使用相机拍照，然后选择使用照片。调用以下方法:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info

在此方法中，我检查图像的 NSData 长度，如果数据 (Kb) 大小太大，则调整实际图像的大小，然后再次检查。这样我只缩小少量以保持最高质量/尺寸的图像而不是特定尺寸 w/h。

问题我正在尝试在“图像缩放”发生时向用户显示一个 HUD。 HUD暂时不显示，这是我试过的。

// Check if the image size is too large
if ((imageData.length/1024) >= 1024) {
    MBProgressHUD *HUD = [MBProgressHUD showHUDAddedTo:self.view animated:YES];
    HUD.dimBackground = YES;
    HUD.labelText = NSLocalizedString(@"HUDHomeLoadingTableData", @"Home View Controller - Loading Table Data");
    HUD.removeFromSuperViewOnHide = YES;

    while ((imageData.length/1024) >= 1024) {
        NSLog(@"While start - The imagedata size is currently: %f KB",roundf((imageData.length/1024)));

        // While the imageData is too large scale down the image

        // Get the current image size
        CGSize currentSize = CGSizeMake(image.size.width, image.size.height);

        // Resize the image
        image = [image resizedImage:CGSizeMake(roundf(((currentSize.width/100)*80)), roundf(((currentSize.height/100)*80))) interpolationQuality:kMESImageQuality];

        // Pass the NSData out again
        imageData = UIImageJPEGRepresentation(image, kMESImageQuality);

    }

    [HUD hide:YES];
}

我正在将 HUD 添加到 self.view 但它没有显示？我是否也应该考虑在这里使用线程，图像缩放是否应该在后台线程上完成并且 HUD 在主线程上更新。我不确定何时确定某些部分是否应该在不同的线程上？

Answer 1

您只调整一张图像的大小吗？还是几个？如果这样做，您可以:

MBProgressHUD *HUD = [self showHUD];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    // do your image resizing here

    // when done, hide the HUD on the main queue

    dispatch_async(dispatch_get_main_queue(), ^{
        [self hideHUD:HUD];
    });
});

哪里

- (MBProgressHUD *)showHUD
{
    MBProgressHUD *HUD = [MBProgressHUD showHUDAddedTo:self.view animated:YES];
    HUD.dimBackground = YES;
    HUD.labelText = NSLocalizedString(@"HUDHomeLoadingTableData", @"Home View Controller - Loading Table Data");
    HUD.removeFromSuperViewOnHide = YES;

    return HUD;
}

- (void)hideHUD:(MBProgressHUD *)HUD
{
    [HUD hide:YES];
}

如果调整一堆图像的大小，您应该定义自己的队列来调整大小:

MBProgressHUD *HUD = [self showHUD];

NSOperationQueue *resizeQueue = [[NSOperationQueue alloc] init];
resizeQueue.maxConcurrentOperationCount = 1;

NSOperation *completeOperation = [NSBlockOperation blockOperationWithBlock:^{

    //when done, hide the HUD (using the main queue)

    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
        [self hideHUD:HUD];
    }];
}];

for (NSInteger i = 0; i < imageCount; i++)
{
    NSOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
        // do your image resizing here
    }];

    // make the completion operation dependent upon each image resize operation

    [completionOperation addDependency:operation];

    // queue the resize operation

    [resizeQueue addOperation:operation];
}

// when all done, queue the operation that will remove the HUD

[resizeQueue addOperation:completionOperation];

请注意，我假设您一次(连续)执行一个操作，但如果您想同时执行这些操作，只需将 maxConcurrentOperationCount 调整为您想要的任何值即可。坦率地说，考虑到这一切的重点是您希望使巨大的图像变小，您可能不想同时运行太多图像(因为内存使用问题)，但这是一种选择。