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I have the following scenario for exporting Core Data entities to JSON and displaying a progress bar while doing so.

Sometimes, after the sheet with the progress bar is dismissed when the export is completed, i get the follwing warning as a console message:

CoreAnimation: warning, deleted thread with uncommitted CATransaction; set CA_DEBUG_TRANSACTIONS=1 in environment to log backtraces.

AppDelegate.m

//  AppDelegate.m

- (void)exportAsJSON:(id)sender;
{
    NSSavePanel *savePanel = [NSSavePanel savePanel];

    [savePanel beginSheetModalForWindow:[self window] completionHandler:^(NSInteger result) {
        WMJSONExportOperation *operation = nil;

        if (result == NSFileHandlingPanelOKButton)
        {
            [_progressIndicator setDoubleValue:0];
            operation = [[WMJSONExportOperation alloc] init];

            // setProgressCallbackBlock
            [operation setProgressCallbackBlock: ^(double progress) {
                [[NSOperationQueue mainQueue] addOperationWithBlock:^
                 {
                     [_progressIndicator setDoubleValue: progress];
                 }];
            }];

            // setExportCompletionBlock
            [operation setExportCompletionBlock:^(NSData *data, NSError *error) {
                // Insert code here to save data to disk
                [_window endSheet:_exportProgressSheet];
            }];

            [_window beginSheet:_exportProgressSheet completionHandler:^(NSInteger result) {
                NSLog(@"ExportProgressSheet completionHandler executed");
            }];

            NSOperationQueue *queue;
            queue = [[NSOperationQueue alloc] init];
            [queue addOperation:operation];
        }

    }];
}

WMJSONExportOperation.m, a subclass of NSOperation:

- (void)main;
{
    NSError *error = nil;
    NSData *data = nil;

    // just for illustrating the problem:
    for (int i=1; i<=10; i++) {
        sleep(1);
        [self progressCallbackBlock](i * 10);
    }

    [self exportCompletionBlock](data, error);
}

@end

So the first question is: It is just a warning, should I care?

The second question is, how to avoid the warning. There are questions on SO describing similar problems, but the suggested solution is often to manipulate the NSProgressIndicator only from the main queue. Isn't that exactly what I am doing with this code:

    // setProgressCallbackBlock
    [operation setProgressCallbackBlock: ^(double progress) {
        [[NSOperationQueue mainQueue] addOperationWithBlock:^
         {
             [_progressIndicator setDoubleValue: progress];
         }];
    }];
4

1 回答 1

0

通过设置 CA_DEBUG_TRANSACTIONS 环境变量进一步调查消息后，我发现问题不是发送到的消息NSProgressIndicator，而是工作表的关闭，我确实从主队列之外的另一个队列触发。

所以这个改变解决了我的问题：

[_window endSheet:_exportProgressSheet];

变成：

[[NSOperationQueue mainQueue] addOperationWithBlock:^
   {
      [_window endSheet:_exportProgressSheet];
   }];
于 2015-04-29T13:00:04.863 回答