在视图之间使用单例共享数据/字符串

问题描述

我正在尝试在我的iPhone项目中的两个视图之间共享一个字符串。如果我在字符串中使用实际的@something here，它目前有效，但如果我想使用像label.text这样的东西，它甚至不会是一个字符串。

I'm trying to share a string between two views on my iPhone project. It currently works if I use the actual @"something here" for the string, but if I want to use something like label.text, it doesn't even though it is still a string.

我会告诉你我需要做些什么来更清楚。

I'll show you what I have to make it clearer.

第一视图：Info_ViewController.h

First View: Info_ViewController.h

#import <UIKit/UIKit.h>

@interface Info_ViewController : UIViewController {

    IBOutlet UITextField *locationField;

}

@property (nonatomic, retain) NSString *locationString;

+ (id)sharedInfoVC;

@end

第一视图：Info_ViewController.m

First View: Info_ViewController.m

#import "Info_ViewController.h"

static Info_ViewController *sharedInfoVC = nil;

@implementation Info_ViewController
@synthesize locationString;


#pragma mark Singleton Methods
+ (id)sharedInfoVC {
    @synchronized(self) {
        if (sharedInfoVC == nil)
            sharedInfoVC = [[self alloc] init];
        }
    return sharedInfoVC;
}

- (id)init {
    if (self = [super init]) {
        locationString = [[NSString alloc] initWithString:locationField.text]; //This is there part I mentioned earlier, when using @"something" instead of locationField.text works.
    }
    return self;
}

第二个视图：Confirm_ViewController.m

Second View: Confirm_ViewController.m

#import "Confirm_ViewController.h"
#import "Info_ViewController.h"

@implementation Confirm_ViewController

- (IBAction)buttonZ:(id)sender
{
    Info_ViewController *infoVCmanager = [Info_ViewController sharedInfoVC];
    locationLabel.text = infoVCmanager.locationString;
}

我现在把它放在一个按钮下，但它最终将在viewDidLoad下。
如果你用一个字符串（@blahblahblah）替换locationField.text，它将不会崩溃并且有效。

I put it under a button for now, but it will eventually be under viewDidLoad.If you replace locationField.text with a string (@"blahblahblah") it won't crash and works.

当它崩溃时我得到错误：节目收到的信号：SIGABRT

When it crashes I get the error: Program received signal: "SIGABRT"

编辑：我尝试更改

initWithString:locationField.text

to

initWithFormat:@"%@",locationField.text

现在我在第二个视图中的标签打印（NULL）

and now it my label in the second view prints "(NULL)"

感谢您花时间提供建议，我真的很感激。

Thanks for taking the time to give advice, I really appreciate it.

推荐答案

将nil作为格式字符串传递给 - [NSString initWithString]是错误的。

It is an error to pass nil as the format string to -[NSString initWithString].

那你怎么通过nil？实际上你有两个的Info_ViewController实例。你有一个实例，它是你的应用程序的正常部分，然后你还有一个第二个实例，它是你的单身人士（它实际上不再是单身人士）。

So how are you passing nil? You actually have two instances of Info_ViewController. You have the one instance which is the normal part of your app, and then you also have a second instance which is your "singleton" (which really isn't a singleton any more).

所以在你的单例实例中，UITextField是nil（并且将始终为nil），所以locationField.text为nil，你将它传递给initWithString：，这是一个崩溃。事实上，单身人士甚至没有完全像视图控制器一样。

So in your "singleton" instance, the UITextField is nil (and will always be nil) and so locationField.text is nil and you are passing that to initWithString:, which is a crash. In fact the "singleton" isn't even fully baked as view controller's go.

如果你想让单身人士在你的应用程序的其他地方共享数据，那真的不应该是Info_ViewController或任何类型的视图控制器。它应该是您用来管理数据的其他类。我会创建另一个类并将其实现为单例。

If you want a singleton to share data elsewhere in your app, it really should not be a Info_ViewController or any type of view controller. It should be of some other class that you use to manage your data. I would create another class and implement that as a singleton.

希望这可以帮助您了解这里发生的事情。

Hope that helps you understand what's happening here.

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