在Objective-C中将一个ViewController中的值传递给另一个ViewController [英] Pass a value from one ViewController to another in Objective-C

问题描述

我对Objective-C编程很新。我现在忍受的一件事是将第一个 ViewController 中的值传递给下一个。

I'm fairly new to Objective-C, programming. The one thing, I'm currently putting up with is passing a value from the first ViewController to the next one.

我在这里阅读此条目，但这对我没有帮助。这很有趣，因为他的回答有近500票，所以我一定是个问题。我做的是以下。

I've read this entry here and it didn't help me. Which is funny, since his answer has nearly 500 votes, so I must be the problem. What I did was the following.

我打开了我的 PreviewViewController.m 并添加了以下行 #importMainViewController.h因为我想将 PreviewViewController 中的值传递给`MainViewController。然后，当我切换布局（成功工作）时，我想传递一个值。

I opened my PreviewViewController.m and added the following line #import "MainViewController.h" since I wanted to pass a value from the PreviewViewController to the `MainViewController. Then, when I switch the layouts ( which successfully works ) I want to pass a value.

MainViewController  *mainViewController     = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
mainViewController.userId                   = @"539897197";

如您所见，我想传递userId。为此，我还在 MainViewController.h中创建了一个属性

As you can see, I want to pass the userId. For that, I also created a property in the MainViewController.h

@property ( nonatomic, strong ) NSString *userId;

现在，在我的 MainViewController.m I想要访问userId。但是当我记录它时，控制台告诉我它是 null 。但是，当我在 NSLog 之前设置变量时，它起作用，所以似乎传递是问题。

Now, In my MainViewController.m I want to access the userId. But when I log it, the console tells me it is null. However, when I set the variable right before the NSLog it works, so it seems like the passing is the problem.

另外在 MainViewController.m 我有以下行

@synthesize userId = _userId; 

但即使我删除了该行并更改了 NSLog 到 NSLog（@％@，self.userId）; 发生了同样的问题。

but even when I removed that line and changed the NSLog to NSLog(@"%@",self.userId); the same problem occurred.

如何成功传递变量？我做错了哪一步？

How can I successfully pass the variables? Which step am I doing wrong?

编辑
这是我切换布局的方式

EDIT This is how I switch the layouts

UIViewController    *viewController         = [[MainViewController alloc]init];
MainViewController  *mainViewController     = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
mainViewController.userId                   = @"539897197";
[self presentViewController:viewController animated:YES completion:NULL];

推荐答案

为什么不创建自定义初始化程序并将其传递给办法？类似

Why not create a custom initializer and pass it in that way? Something like

- (id)initWithUserId:(NSString *)aUserId {
    self = [super initWithNibName:@"MainViewController" bundle:nil];
    if (self) {
        self.userId = aUserId
    }
    return self;
}

然后你就可以这样做：

MainViewController *mvc = [[MainViewController alloc] initWithUserId:@"1234"]
[self presentViewController:mvc animated:YES completion:nil];

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