在同一VC上保留变量值，但在更改VC ObjectiveC后清除该值

Question

我的Classes VC在顶部有一个不同日期的分段控件。当用户点击日期时，它会根据dtDate加载内容并调用LoadClasses方法。

现在我有另一个Search VC，当点击搜索时，它会以string传递给Classes VC我正在使用NSDefault for key txtURLFromSearch保存string和在NSDefault for key txtURLFromSearch

回调Classes VC

之后，我将字符串等同于sURLFromSearch，我希望将其保留在Classes VC但是当用户关闭此VC时，我希望清除NSDefault的字符串值以获取密钥txtURLFromSearch

我将使用sURLFromSearch进行一些检查，它会追加并加载sURL或只是默认的sURL。

我想要实现的目标：

1. 当USER退出Classes VC时如何清除NSDefault for key txtURLFromSearch

2. 是否有更好的方法将数据从Search VC推送到Classes VC。该字符串将保留在Classes VC，但当用户解除Classes VC时，显示Classes VC的所有字符串值？



@synthesize sURL;
@synthesize sURLFromSearch;

- (void)viewDidLoad
{
    [super viewDidLoad];

    dtDate = [[NSMutableArray alloc] init];

    [self setupSegmentButtons];

    NSDate *now = [NSDate date];
    NSDateFormatter *dateFormatter=[[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"dd/MM/YYYY"];
    sDtDate = [dateFormatter stringFromDate:now];

    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    sURLFromSearch = [defaults objectForKey:@"txtURLFromSearch"];

    NSLog(@"=====%@******",sURLFromSearch);

    [self LoadClasses];
}

-(void)viewWillAppear:(BOOL)animated {

    //=== Is there something I need to do here?
}

-(void)viewWillDisappear:(BOOL)animated{

    [super viewWillDisappear:animated];
    //=== The following doesn't work, when I switch back to this View, 
    //=== It will set txtURLFromSearch to Empty String. 
    //NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    //[defaults setObject:@"" forKey:@"txtURLFromSearch"];
    //[defaults synchronize];
}

- (void)LoadClasses {

    NSLog(@"======sURLFromSearch====%@**********", sURLFromSearch);

    if ([sURLFromSearch length] !=0 ) {

       //=====sURL 1=======
       sURL = [sURL stringByAppendingString:sURLFromSearch];

       NSLog(@"==== sURL1: %@ ", sURL);

    } else {

       //=====sURL 2=======
       sURL        
    }

NSURL *url = [NSURL URLWithString:sURL];
NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
[webView loadRequest:urlRequest];
[webView setDelegate:(id<UIWebViewDelegate>)self];

UIRefreshControl *refreshControl = [[UIRefreshControl alloc] init];
[refreshControl addTarget:self action:@selector(handleRefresh:) forControlEvents:UIControlEventValueChanged];
[webView.scrollView addSubview:refreshControl];

}

- (void)handleRefresh:(UIRefreshControl *)refresh {

    NSURL *url = [NSURL URLWithString:sURL];
    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
    [webView loadRequest:urlRequest];
    [refresh endRefreshing];
}

从搜索VC传递字符串。

- (IBAction)btnSearch:(UIButton *)sender {

    sURL = @"From Search, append to Classes sURL";

    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    [defaults setObject:sURL forKey:@"txtURLFromSearch"];
    [defaults synchronize];

    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    UITabBarController *tabView = [storyboard instantiateViewControllerWithIdentifier:@"profileView"];
tabView.selectedIndex=1;
    [self presentViewController:tabView animated:YES completion:nil];

    Classes *vc = [[Classes alloc] init];
    [vc fromSearch:sURL];

}