ios - 调用 [self.navigationController pushViewController :animated:] 时需要很长时间将 UIView 推送到 UINavigation Controller

Question

我试图通过调用 UINavigationController 的这个方法将一个 UIView 推送到另一个 UIView 上:

signupPageObj = [[SignupPage alloc]initWithNibName:@"SignupPage" bundle:nil];
[self.navigationController pushViewController:signupPageObj animated:YES]; 

但它在加载我的 SignUpPage UIView 时卡住了一段时间。我不知道是什么原因，但因为我在 viewDidLoad 和方法 initWithNibName 中没有太多自定义。

initWithNibName 的完整代码如下:

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];

    if (self) 
    {
        statusArray=[[NSMutableArray alloc] init];
        UILabel *labelforNavigationTitle = [[UILabel alloc] initWithFrame:CGRectZero];
        labelforNavigationTitle.backgroundColor = [UIColor clearColor];
        labelforNavigationTitle.font = [UIFont fontWithName:FONTSAVINGSBOND size:30.0];
        labelforNavigationTitle.shadowColor = [UIColor colorWithWhite:0.0 alpha:0.5];
        labelforNavigationTitle.textAlignment = UITextAlignmentCenter;
        labelforNavigationTitle.textColor = [UIColor whiteColor]; // change this color
        self.navigationItem.titleView = labelforNavigationTitle;
        labelforNavigationTitle.text = NSLocalizedString(@"Sign Up", @"");
        [labelforNavigationTitle sizeToFit];

    }
    return self;

}


-(void)viewDidLoad
{

    [super viewDidLoad];

    self.fullPathToFile=@"";
    self.gender=@"";
    strForGender=self.gender;
    labelInDatePicker.font=[UIFont fontWithName:FONTCENTURYGOTHICBOLD size:17.0];


    UIImage* imageCancel = [UIImage imageNamed:@"cancelbtn.png"];
    CGRect frameimg = CGRectMake(0, 0, (imageCancel.size.width)/2, (imageCancel.size.height)/2);


    UIButton *cancelButton = [[UIButton alloc] initWithFrame:frameimg];
    [cancelButton setBackgroundImage:imageCancel forState:UIControlStateNormal];
    [cancelButton addTarget:self action:@selector(cancelButtonclickedInAvtar)
         forControlEvents:UIControlEventTouchUpInside];
    [cancelButton setShowsTouchWhenHighlighted:YES];



    self.pickerBirthdayView.frame=CGRectMake(0,460,320,252);
    [self.view addSubview:self.pickerBirthdayView];

    self.avtarView.frame=CGRectMake(0,460,320,460);
    [self.view addSubview:self.avtarView];
    cancelButtonInAvtarView=[[UIBarButtonItem alloc]initWithCustomView:cancelButton];

    self.termsAndConditionPage.frame=CGRectMake(0,460,320,460);
    [self.view addSubview:self.termsAndConditionPage];


    if ([self.navigationController.navigationBar respondsToSelector:@selector(setBackgroundImage:forBarMetrics:)] ) 
    {
        UIImage *image = [UIImage imageNamed:@"titlebg.png"] ;
        [self.navigationController.navigationBar setBackgroundImage:image forBarMetrics:UIBarMetricsDefault];
    }
    [self performSelector:@selector(settingScrollView) withObject:nil afterDelay:1.0];

    scrollPrevButton.hidden=YES;
    scrollNextButton.hidden=NO;

    isSectionExpanded=NO;
    checkForImage=2;
    termsAndConditionChecked=2;
    checkForBackgroundImage=10;
    start=10;


    UIImage* image1 = [UIImage imageNamed:@"backbtn.png"];
    CGRect frameimg1 = CGRectMake(0, 0, (image1.size.width)/2, (image1.size.height)/2);

    UIButton *backButton = [[UIButton alloc] initWithFrame:frameimg1];
    [backButton setBackgroundImage:image1 forState:UIControlStateNormal];
    [backButton addTarget:self action:@selector(popToRootViewController)
         forControlEvents:UIControlEventTouchUpInside];


    //    UIImage* image2 = [UIImage imageNamed:@"submitbtn.png"];
    //    CGRect frameimg2 = CGRectMake(0, 0, (image2.size.width)/2, (image2.size.height)/2);

    //    UIButton *submitButton = [[UIButton alloc] initWithFrame:frameimg2];
    //    [submitButton setBackgroundImage:image2 forState:UIControlStateNormal];
    //    [submitButton addTarget:self action:@selector(submitButtonPressed:)forControlEvents:UIControlEventTouchUpInside];


    UIImage* imageforTermsandConditionPage = [UIImage imageNamed:@"backbtn.png"];
    CGRect frameimgforTermsandConditionPage = CGRectMake(0, 0, (imageforTermsandConditionPage.size.width)/2, (imageforTermsandConditionPage.size.height)/2);

    UIButton *backButtonforTermsandConditionPage = [[UIButton alloc] initWithFrame:frameimgforTermsandConditionPage];
    [backButtonforTermsandConditionPage setBackgroundImage:imageforTermsandConditionPage forState:UIControlStateNormal];
    [backButtonforTermsandConditionPage addTarget:self action:@selector(backtoSignupPage) forControlEvents:UIControlEventTouchUpInside];



    UIImage* imageforChooseIconPage = [UIImage imageNamed:@"backbtn.png"];
    CGRect frameimgforChooseIconPage = CGRectMake(0, 0, (imageforChooseIconPage.size.width)/2, (imageforChooseIconPage.size.height)/2);

    UIButton *backButtonforChooseIconPage = [[UIButton alloc] initWithFrame:frameimgforChooseIconPage];
    [backButtonforChooseIconPage setBackgroundImage:imageforTermsandConditionPage forState:UIControlStateNormal];
    [backButtonforChooseIconPage addTarget:self action:@selector(backtoSignupPage) forControlEvents:UIControlEventTouchUpInside];



    backButton1 = [[UIBarButtonItem alloc] initWithCustomView:backButton];
    self.navigationItem.leftBarButtonItem = backButton1;

    //    submitButton1=[[UIBarButtonItem alloc]initWithCustomView:submitButton];
    //    self.navigationItem.rightBarButtonItem=submitButton1;

    backButtonInTermsAndCondition=[[UIBarButtonItem alloc]initWithCustomView:backButtonforTermsandConditionPage];
    backButtonInChooseIcon=[[UIBarButtonItem alloc]initWithCustomView:backButtonforChooseIconPage];


    CALayer *layer = [self.objTextView layer];
    [layer setMasksToBounds:YES];
    [layer setCornerRadius:10.0];
    [layer setBorderWidth:0.0];
    [layer setBorderColor:[[UIColor lightGrayColor] CGColor]];
}


-(void)settingScrollView
{
    arrOfImages=[NSArray arrayWithObjects:@"Avtar0.png",@"Avtar1.png",@"Avtar2.png",@"Avtar3.png",@"Avtar4.png",@"Avtar5.png",@"Avtar6.png",@"Avtar7.png",@"Avtar8.png",@"Avtar9.png",nil];

    pageControl.numberOfPages = kNumberOfPages;
    pageControl.currentPage = 0;
    pageControl = [[PageControl alloc] initWithFrame:rect] ;
    pageControl.frame = rect;
    pageControl.delegate=self;
    pageControl.numberOfPages=[arrOfImages count];
    pageControl.currentPage = self.currentPage;
    [self.view addSubview:pageControl];

    scrollV = [[UIScrollView alloc]init];
    scrollV.frame=CGRectMake(35,55,250,246);
    scrollV.backgroundColor=[UIColor clearColor];
    scrollV.delegate=self;
    scrollV.pagingEnabled=YES;
    self.scrollV.contentSize = CGSizeMake(self.scrollV.frame.size.width *kNumberOfPages, 220);

    self.scrollV.showsHorizontalScrollIndicator = NO;
    self.scrollV.showsVerticalScrollIndicator = NO;
    self.scrollV.scrollsToTop = NO;
    self.scrollV.delegate = self;

    [self.avtarView addSubview:scrollV];


    for(int k =0;k<arrOfImages.count;k++)
    {

        UIButton *btn=[UIButton  buttonWithType:UIButtonTypeCustom];
        btn.tag=k;
        btn.imageView.contentMode= UIViewContentModeScaleAspectFit;
        [btn setImage:[UIImage imageNamed:[arrOfImages objectAtIndex:k]] forState:UIControlStateNormal];
        [btn setImage:[UIImage imageNamed:[arrOfImages objectAtIndex:k]] forState:UIControlStateHighlighted];
         btn.frame=CGRectMake((self.scrollV.frame.size.width * k),0, 250,241);
        [btn addTarget:self action:@selector(setImageInScrollView:) forControlEvents:UIControlEventTouchUpInside];
        [self.scrollV addSubview:btn];
    }

}

如果有人对此有建议或解决方案，我将不胜感激。

Answer 1

我注意到您的 settingScrollView 正在加载一堆图像(尤其是当它们很大时)，速度可能很慢。这也是对内存的过度使用。这个问题有两种常见的解决方案:

1. 您可以采用异步图像加载。您可以使用 GCD(或任何并发技术)在后台加载图像，然后将 ImageView image 属性的设置分派(dispatch)回主队列，而不是在主队列中加载图像队列。这解决了性能问题，但没有解决内存问题。

2. 更好的是，您可以使用延迟加载，只加载当前可见图像的图像。然后将您的 View Controller 配置为 UIScrollViewDelegate，当用户滚动到下一张图片时，加载它。你可以做一个加载当前图像和“下一个”图像的变体，当用户滚动到下一个图像时，你会延迟加载新的“下一个”图像。大多数延迟加载技术还采用异步图像加载，这是我的第一个观察结果。

---

更新:

很明显，如果您将以下行替换为:

[self performSelector:@selector(settingScrollView) withObject:nil afterDelay:1.0];

只有:

[self settingScrollView];

但我认为您是出于某种原因延迟了一秒钟。也许您不喜欢加载十张图片所花费的延迟，并且您不想因此而减慢整个用户界面的速度。所以你可以使用我的第一个技术，图像的异步加载，在加载图像时不阻塞用户界面。如果你想这样做，你可以用类似的东西替换 settingScrollView 中的 for 循环:

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

for (int k = 0; k < arrOfImages.count; k++)
{
    UIButton *btn = [UIButton  buttonWithType:UIButtonTypeCustom];
    btn.tag = k;
    btn.imageView.contentMode = UIViewContentModeScaleAspectFit;
    dispatch_async(queue, ^{

        // retrieve the image in a background queue

        UIImage *image = [UIImage imageNamed:[arrOfImages objectAtIndex:k]];

        // and now update the image property in your UI in the main queue

        dispatch_async(dispatch_get_main_queue(), ^{
            [btn setImage:image forState:UIControlStateNormal];
            [btn setImage:image forState:UIControlStateHighlighted];

            btn.frame=CGRectMake((self.scrollV.frame.size.width * k),0, 250, 241);
            [btn addTarget:self action:@selector(setImageInScrollView:) forControlEvents:UIControlEventTouchUpInside];
            [self.scrollV addSubview:btn];
        });
    });
    // btn.frame=CGRectMake((self.scrollV.frame.size.width * k),0, 250, 241);
    // [btn addTarget:self action:@selector(setImageInScrollView:) forControlEvents:UIControlEventTouchUpInside];
    // [self.scrollV addSubview:btn];
}

话虽如此，通过 imageNamed 加载图像通常不会那么慢(尽管如果图像真的很大，它可能会引入一个可观察到的延迟)。但是上面的代码将进一步减少从持久存储加载图像所造成的用户界面延迟。假设您的图像大约为 250x241，性能改进不大(当然，它返回到我的用户界面的速度是原来的十倍，但是由于同步加载图像只用了 0.05 秒，而异步加载它们，我的 UI 返回了0.005 秒)。这种技术在拍摄真正流畅的 tableview 滚动时非常有用，或者如果从网络加载图像，但不清楚它是否值得在这里使用(除非你的图像很大)。

我不会处理我的第二点，图像的延迟加载，除非你告诉我们你有内存问题。如果是这种情况，我们将用 imageWithContentsOfFile 替换 imageNamed 方法(因为 imageNamed 是一个非常粗糙的缓存系统)并将其包装在适当的延迟加载方案。但是只有十张图片，您可能不需要去那里。因此，除非您回来告诉我们您有严重的内存问题，否则我将推迟该解决方案。