从后台打开应用程序时不会调用 ViewDidAppear

问题描述

我有一个视图控制器，其中我的值为 0(标签)，当我从另一个 ViewController 打开该视图控制器时，我已将 viewDidAppear 设置为 20标签.它工作正常但是当我关闭我的应用程序然后我再次打开我的应用程序但值没有改变因为 viewDidLoad、viewDidAppear 和 viewWillAppear什么都没有被调用.当我打开我的应用程序时如何调用.我必须从 applicationDidBecomeActive 做任何事情吗?

I have a View Controller in which my value is 0 (label) and when I open that View Controller from another ViewController I have set viewDidAppear to set value 20 on label. It works fine but when I close my app and than again I open my app but the value doesn't change because viewDidLoad, viewDidAppear and viewWillAppear nothing get called. How can I call when I open my app. Do I have to do anything from applicationDidBecomeActive?

推荐答案

出于对事件的确切顺序感到好奇，我按如下方式检测了一个应用程序:(@Zohaib，您可以使用下面的 NSNotificationCenter 代码来回答您的问题).

Curious about the exact sequence of events, I instrumented an app as follows: (@Zohaib, you can use the NSNotificationCenter code below to answer your question).

// AppDelegate.m

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    NSLog(@"app will enter foreground");
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    NSLog(@"app did become active");
}

// ViewController.m

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"view did load");

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appDidBecomeActive:) name:UIApplicationDidBecomeActiveNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillEnterForeground:) name:UIApplicationWillEnterForegroundNotification object:nil];
}

- (void)appDidBecomeActive:(NSNotification *)notification {
    NSLog(@"did become active notification");
}

- (void)appWillEnterForeground:(NSNotification *)notification {
    NSLog(@"will enter foreground notification");
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    NSLog(@"view will appear");
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    NSLog(@"view did appear");
}

启动时，输出如下所示:

At launch, the output looks like this:

2013-04-07 09:31:06.505 myapp[15459:11303] view did load
2013-04-07 09:31:06.507 myapp[15459:11303] view will appear
2013-04-07 09:31:06.511 myapp[15459:11303] app did become active
2013-04-07 09:31:06.512 myapp[15459:11303] did become active notification
2013-04-07 09:31:06.517 myapp[15459:11303] view did appear

进入背景然后重新进入前景:

Enter the background then reenter the foreground:

2013-04-07 09:32:05.923 myapp[15459:11303] app will enter foreground
2013-04-07 09:32:05.924 myapp[15459:11303] will enter foreground notification
2013-04-07 09:32:05.925 myapp[15459:11303] app did become active
2013-04-07 09:32:05.926 myapp[15459:11303] did become active notification

这篇关于从后台打开应用程序时不会调用 ViewDidAppear的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！