点击图片时抛出的错误

Question

基本上遵循本教程https://parse.com/tutorials/saving-images。当用户点击一个图像时，它会带他们到一个新的视图控制器并全屏显示这个图像。当我点击图片时，它会把我带到一个黑屏，并抛出以下错误

Warning: A long-running Parse operation is being executed on the main thread. 
 Break on warnParseOperationOnMainThread() to debug.

我检查过了，它将图片发送到新的视图控制器所以它可能与VC本身有关。我在它要求我的地方放了一个断点，下面是线程说的

`My App`warnParseOperationOnMainThread at PFTask.m:15:
0x95fa0:  pushl  %ebp
0x95fa1:  movl   %esp, %ebp
0x95fa3:  subl   $0x8, %esp
0x95fa6:  calll  0x95fab                   ; warnParseOperationOnMainThread + 11 at PFTask.m:15
0x95fab:  popl   %eax
0x95fac:  leal   0x18771d(%eax), %eax
0x95fb2:  movl   %eax, (%esp)
0x95fb5:  calll  0x98d54                   ; symbol stub for: NSLog
0x95fba:  addl   $0x8, %esp
0x95fbd:  popl   %ebp
0x95fbe:  retl  

第五个线程指向我的一个类中的一个名为buttonTouched的方法。它指向这行代码:

imageData = [theImage getData];

方法如下:

- (void)buttonTouched:(id)sender {
    // When picture is touched, open a viewcontroller with the image
    PFObject *theObject = (PFObject *)[allImages objectAtIndex:[sender tag]];
    PFFile *theImage = [theObject objectForKey:@"imageFile"];
    NSData *imageData = [[NSData alloc] init];
    imageData = [theImage getData];
    UIImage *selectedPhoto = [UIImage imageWithData:imageData];
    PhotoDetailViewController *pdvc = [[PhotoDetailViewController alloc] init];
    pdvc.selectedImage = selectedPhoto;
    [self presentViewController:pdvc animated:YES completion:nil];
    NSLog(@"Photo controller %@", pdvc.selectedImage);
}

快把我逼疯了。一切几乎都是相同的教程。还是需要定义到2vc的segue关系?如果相关的话，我会使用故事板。

一个很好的解释这是怎么发生的和一个解决方案将是很棒的。

Answer 1

出现警告是因为您正在主线程中下载图像。您可以在后台下载它，并在下载完成后呈现视图，如下所示。

- (void)buttonTouched:(id)sender {
    // When picture is touched, open a viewcontroller with the image
    PFObject *theObject = (PFObject *)[allImages objectAtIndex:[sender tag]];
    PFFile *theImage = [theObject objectForKey:@"imageFile"];
    [theImage getDataInBackgroundWithBlock:^(NSData *data, NSError *error) {
        UIImage *selectedPhoto = [UIImage imageWithData:imageData];
        PhotoDetailViewController *pdvc = [[PhotoDetailViewController alloc] init];
        pdvc.selectedImage = selectedPhoto;
        [self presentViewController:pdvc animated:YES completion:nil];
        NSLog(@"Photo controller %@", pdvc.selectedImage);
    }];
}

另一种解决这个问题的方法是，你可以将PFObject传递给呈现的视图，并在加载后下载该视图上的图片。