Question

我遇到了更新我创建的“myInfoBox”对象内容的问题，以便在完成某些后台进程时显示。

在委托方法中，我正在创建一个新的viewController：

-(void)loadMainView
{
        myFirstViewController = [[MyFirstViewController alloc] initWithNibName:@"MyFirstView" bundle:nil];      
        navigationController = [[UINavigationController alloc] initWithRootViewController:myFirstViewController];
        // myFirstViewController was retained again by the controller, release one
        [myFirstViewController release];
        navigationController.navigationBar.hidden = YES;
        [window addSubview:navigationController.view];
        [window makeKeyAndVisible];
        // the next method is run after the "viewDidLoad" is finished loading
        [myFirstViewController loadAlertViewForNewUser];
}

以下是我的“myFirstViewController”实现，它创建了一个“infoBox”类的实例（稍后我会显示它的代码）：

- (void)viewDidLoad {

        self.navigationController.navigationBar.frame = CGRectMake(0, 0, 0, 0);
        self.navigationController.navigationBar.bounds = CGRectMake(0, 0, 0, 0);

        self.myInfoBox = [[InfoBoxController alloc] initWithNibName:@"InfoBox" bundle:[NSBundle mainBundle]];
        CGRect infoBoxFrame;
        infoBoxFrame = CGRectMake(60, 120, 200, 200);
        myInfoBox.view.frame = infoBoxFrame;

        myInfoBox.i_statusLabel.text = @"Downloading Account Updates";
        myInfoBox.i_titleLabel.text = @"Updating";
// disabled for testing
        //myInfoBox.view.hidden = YES;
        [self.view addSubview:myInfoBox.view];
        [super viewDidLoad];
    }

// this method is called after the view has been loaded by the delegate
- (void)loadAlertViewForNewUser
{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Welcome!" message:@"Connect to download stuff from your account?"
                                                   delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"OK", nil];
    alert.tag = 0;
    [alert show];
}

// implementation of the alertview delegate
- (void)alertView:(UIAlertView *)actionSheet didDismissWithButtonIndex:(NSInteger)buttonIndex
{
    if (actionSheet.tag == 0)
    {
        if (buttonIndex == 0) 
        { NSLog(@"button 0 was pressed"); }
        if (buttonIndex == 1) 
        {
// this is the button that is pressed
            [actionSheet removeFromSuperview];
            [actionSheet release];

// tried using this also
            //[self performSelectorOnMainThread:@selector(userInitialSetupMainThread) withObject:nil waitUntilDone:NO];
// do stuff and update the infobox about it
            [self loadInfoBoxInitialUserSetup];
// tried using this as well
            //[self performSelectorInBackground:@selector(loadInfoBoxInitialUserSetup) withObject:nil];
        }
        return;
    }
}

- (void)loadInfoBoxInitialUserSetup
{
    [self performSelectorOnMainThread:@selector(userInitialSetupMainThread) withObject:nil waitUntilDone:NO];
}

- (void)userInitialSetupMainThread
{
    // fetch JSON data
    NSDictionary *responseJSON = [NSDictionary dictionaryWithDictionary:[self getUserstuff]];

    self.myInfoBox.i_statusLabel.text = @"Processing Recieved information";
// breakpoint - nothing changes in the view on the simulator
    [myInfoBox.view setNeedsLayout];
// breakpoint - nothing changes in the view on the simulator
    [myInfoBox.view setNeedsDisplay];
// breakpoint - nothing changes in the view on the simulator
    [myInfoBox.parentViewController.view setNeedsLayout];
// breakpoint - nothing changes in the view on the simulator
    [myInfoBox.parentViewController.view setNeedsDisplay];
// breakpoint - nothing changes in the view on the simulator
    [myInfoBox performSelectorOnMainThread:@selector(updateValuesForTitle:) withObject:@"test" waitUntilDone:YES];
// breakpoint - nothing changes in the view on the simulator
    [self.view setNeedsLayout];
// breakpoint - nothing changes in the view on the simulator
    [self.view setNeedsDisplay];
// breakpoint - nothing changes in the view on the simulator
    self.myInfoBox.i_statusLabel.text = @"Reloading...";        
// breakpoint - nothing changes in the view on the simulator
    [self readStuffFromDB]; 
    sleep(2);
//disabled view removal for testing..
    //[self.myInfoBox.view removeFromSuperview];
// breakpoint - nothing changes in the view on the simulator
}

在测试中发生的情况是，当 - （void）loadMainView方法完成时，myInfoBox对象在屏幕上创建，然后我可以在屏幕上看到后面的alertView中的“myInfoBox”（用于测试...）此时屏幕响应，我可以选择YES，一旦我选择是，调用委托方法。正如我在源文件中所评论的那样，使用断点我正在监视模拟器并遵循代码，当我仍然在 - （void）userInitialSetupMainThread方法中时，从未反映出更改的标签值，但是一旦完成视图更新使用最新的.text值!!哎呀..

此外，myInfoBox类的源：

@interface InfoBoxController : UIViewController {
    IBOutlet UILabel* i_titleLabel;
    IBOutlet UILabel* i_statusLabel;
    IBOutlet UIImageView* i_loadingImage;
    IBOutlet UIImageView* i_background;
    IBOutlet UIActivityIndicatorView* i_activityIndicator;
}

@property(nonatomic, retain) IBOutlet UILabel* i_titleLabel;
@property(nonatomic, retain) IBOutlet UILabel* i_statusLabel;
@property(nonatomic, retain) IBOutlet UIImageView* i_loadingImage;
@property(nonatomic, retain) IBOutlet UIImageView* i_background;
@property(nonatomic, retain) IBOutlet UIActivityIndicatorView* i_activityIndicator;

//- (void)updateValuesForTitle:(NSString *)title Label:(NSString *)label;
- (void)updateValuesForTitle:(NSString *)title;

@end

@implementation InfoBoxController

@synthesize i_titleLabel, i_statusLabel, i_loadingImage, i_background;
@synthesize i_activityIndicator;

//-(void)updateValuesForTitle:(NSString *)title Label:(NSString *)label
-(void)updateValuesForTitle:(NSString *)title
{
    self.i_titleLabel.text = title;
    self.i_statusLabel.text = title;
    [self.i_titleLabel setNeedsDisplay];
    [self.i_statusLabel setNeedsDisplay];
}

抱歉LOONG帖子:) 请帮忙！

Answer 1

冒着听起来无益的风险，这就是它的工作方式。如果您在主事件循环中有长时间运行的代码（即，您没有显式创建线程或类似代码），操作系统将无法更新UI。

要在代码运行时更新UI，您需要使用线程NSOperationQueue等在后台运行复杂操作，或者将其分解为更小的步骤并将控制权返回给主循环偶尔也可以更新UI。

从nib加载的视图在方法中运行时不会更新UILabel的内容

1 个答案: