NSOpenPanel冻结应用程序几秒钟

    NSOpenPanel *op=[NSOpenPanel openPanel];
    [op setDelegate:self];
    [op setCanChooseFiles:YES];
    [op setCanChooseDirectories:YES];
    [op setAllowsMultipleSelection:YES];
    [op setPrompt:NSLocalizedString(@"Scan this",@"button of 'scan folder' open panel")];
    [op setAccessoryView:nil];
    [op setMessage:@""];

    if ( [op runModalForDirectory:nil file:nil] == NSOKButton )
    {
        [self scanPaths:[op filenames] automatic:NO];
        [[ScanController sharedController] setCurrentScanSidebarDriveName: @"(Custom)"];
    } else {
        NSLog(@"cancel clicked");
    }

当我点击“取消”时,应用程序运行到我的方法结束,然后冻结一段时间(几秒钟)。我想这部分代码没问题。还是不呢?当它掉下来时,我的调试器会变得疯狂(At&T…)。:有什么方法可以调试这种问题吗?有人看到了吗?