顯示HUD，而圖像縮小的大小

Question

我有一個應用程序，用戶使用相機拍攝照片，然後選擇使用照片。下面的方法被稱爲：

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

在這個方法中我檢查NSData長度的圖像和調整的實際圖像如果數據（KB）尺寸過大，然後再次檢查。這樣我只能縮小量以保持最高質量/尺寸的圖像，而不是特定的尺寸w/h。

問題 我正嘗試在'圖像縮放'發生時向用戶顯示HUD。 HUD目前沒有顯示，這是我嘗試過的。

// 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]; 
} 

我將HUD添加到self.view中，但它不顯示？我是否應該考慮在這裏進行線程化，如果圖像縮放是在後臺線程上完成的，並且HUD在主體上更新。我不確定何時確定某些部分是否應在不同的線程上？

Answer 1

呼叫在後臺線程縮放方法是這樣的：

if ((imageData.length/1024) >= 1024) { 
    self.HUD = [MBProgressHUD showHUDAddedTo:self.view animated:YES]; 
    HUD.dimBackground = YES; 
    HUD.labelText = NSLocalizedString(@"HUDHomeLoadingTableData", @"Home View Controller - Loading Table Data"); 
    HUD.removeFromSuperViewOnHide = YES; 
    self.scaledImageData = imageData; 
    [self performSelectorInBackground:@selector(scaleDown:) withObject:imageData]; 
} 

-(void)scaleDown:(NSData*)imageData 
{ 
    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 
    self.scaledImageData = UIImageJPEGRepresentation(image, kMESImageQuality); 

    } 

    //hide the hud on main thread 
    [self performSelectorOnMainThread:@selector(hideHUD) withObject:nil waitUntilDone:NO]; 
} 

-(void)hideHUD 
{ 
    [self.HUD hide:YES]; 
} 

Answer 2

你調整隻有一個形象？還是幾個？如果做一個，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]; 
    }); 
}); 

凡

- (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]; 
} 

如果調整了一堆圖像，你應該定義你自己的隊列做調整大小：

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]; 

注意，我假設你要一次一個地完成它們，但是如果你想同時完成它們，只需將maxConcurrentOperationCount調整爲你想要的值即可。坦率地說，考慮到整個這一點，你想要縮小圖像大小，你可能不會想同時運行太多（因爲內存使用的擔憂），但它是一個選項。