使用未定义标识符Use of undeclared identifier

问

I first created a property in my SecondViewController.h file using首先在我的SecondViewController.h文件中创建了一个属性

@property (weak, nonatomic) IBOutlet UIWebView *webView;

And then synthesised it in the corresponding .m file using然后使用相应的.m文件合成它

@property (weak, nonatomic) IBOutlet UIWebView *webView;

I then created a function to create a webpage using a string which the user would cast as an argument. The function:然后，我创建了一个函数来使用字符串创建网页，用户可以将其作为参数进行转换。功能：

void createWebpage(NSString *webString) {
  NSURL *url = [NSURL URLWithString:webString];
  NSURLRequest *requestUrl = [NSURLRequest requestWithURL:url];
  [webView loadRequest:requestUrl];
  }

And where it is called.调用位置。

- (void)viewDidLoad {
    createWebpage(@"http://www.google.com");
    [super viewDidLoad];  // Do any additional setup after loading the view, typically from a nib.
  }

However, in the last line of the function, [webView loadRequest:requestUrl];, webView produces the error "Use of undeclared identifier 'webView'. Why is this, and how can I fix it? All help appreciated.但是，在函数的最后一行[webView loadRequest:requestUrl];，webView会产生错误“使用未定义的标识符'webView'。为什么会这样，我该如何解决？所有帮助都表示赞赏。

答

You are declaring a property which is a available in an object. But you are declaring a simple C method:您定义属性是对象中可用的。但是你要定义了一个简单的C方法：

void createWebpage(NSString *webString) {
  NSURL *url = [NSURL URLWithString:webString];
  NSURLRequest *requestUrl = [NSURLRequest requestWithURL:url];
  [webView loadRequest:requestUrl];
  }

This method will be executed in a "global context" but not on the object. So you can't access the objects properties.此方法将在“全局上下文”中执行，但不在对象上执行。因此您无法访问对象属性。

而是使用一种方法：

Instead use a method:

- (void) createWebpage:(NSString *)webString {
      NSURL *url = [NSURL URLWithString:webString];
      NSURLRequest *requestUrl = [NSURLRequest requestWithURL:url];
      [self.webView loadRequest:requestUrl];
  }

And you have to use self to refer to the current object when you're accessing a property.

You can then call this method:当您访问属性时，必须使用self来引用当前对象。

然后，您可以调用此方法：

[self createWebpage:@"http://www.google.com"];

I really recommend you to read this: https://developer.apple.com/library/mac/documentation/cocoa/conceptual/ProgrammingWithObjectiveC/Introduction/Introduction.html

答

void createWebpage is not a instance method, so the instance variables (such as webView) won't be accessible from there.
You must declare the method as: -(void)createWebpage:(NSString *)webString, and call it as [self createWebPage:@"http://www.google.com"];void createWebpage不是实例方法，因此webView无法从那里访问实例变量（例如）。
您必须将方法声明为：-(void)createWebpage:(NSString *)webString，并将其命名为[self createWebPage:@"http://www.google.com"];

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