Ios UIWebView的后退按钮

我试图创建一个左导航按钮，将我的webview发送回一个页面，但在尝试编译theos时，会抛出以下错误：

在类型为“DDRootViewController*”的对象上未找到属性“webView”，如果（[self.webView canGoBack]）{

我使用的代码如下，如有任何帮助，将不胜感激：）

DDRootControllerView.m

#import "DDRootViewController.h"

@implementation DDRootViewController

- (void)viewDidLoad{

    [super viewDidLoad];

        //Create UIWebView
            UIWebView *webView = [[UIWebView alloc]initWithFrame:self.view.frame];
            webView.delegate = self;
            [webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"https://dylanduff.github.io/WidgetStore/"]]];
            [self.view addSubview:webView];
            webView.backgroundColor = [UIColor whiteColor];

            //NSString *theTitle=[webView stringByEvaluatingJavaScriptFromString:@"document.title"];
            self.title = @"Widget Store";

        //Create back button
            //self.navigationItem.leftBarButtonItem = [[[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addButtonTapped:)] autorelease];


}

- (void)updateBackButton {
    if ([self.webView canGoBack]) {
        if (!self.navigationItem.leftBarButtonItem) {
            [self.navigationItem setHidesBackButton:YES animated:YES];
            UIBarButtonItem *backItem = [[[UIBarButtonItem alloc] initWithTitle:@"<" style:UIBarButtonItemStylePlain target:self action:@selector(backWasClicked:)] autorelease];
            [self.navigationItem setLeftBarButtonItem:backItem animated:YES];
        }
    }
    else {
        [self.navigationItem setLeftBarButtonItem:nil animated:YES];
        [self.navigationItem setHidesBackButton:NO animated:YES];
    }
}

- (void)webViewDidStartLoad:(UIWebView *)webView {
    [self updateBackButton];
}

- (void)webViewDidFinishLoad:(UIWebView *)webView {
    [self updateBackButton];
}

- (void)backWasClicked:(id)sender {
    if ([self.webView canGoBack]) {
        [self.webView goBack];
    }
}


@end

@interface DDRootViewController : UIViewController
<UIWebViewDelegate> {}
@end

#导入“DDRootViewController.h”
@DDRootViewController的实现
-（无效）viewDidLoad{
[超级视图下载]；
//创建UIWebView
UIWebView*webView=[[UIWebView alloc]initWithFrame:self.view.frame]；
webView.delegate=self；
[webView loadRequest:[NSURLRequestRequestWithURL:[NSURL URLWithString:@]https://dylanduff.github.io/WidgetStore/"]]];
[self.view addSubview:webView]；
webView.backgroundColor=[UIColor whiteColor]；
//NSString*theTitle=[webView stringByEvaluatingJavaScriptFromString:@“document.title”]；
self.title=@“小部件存储”；
//创建后退按钮
//self.navigationItem.leftBarButtonItem=[[[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarbuttonSystemAddTarget:self action:@selector（addButtonTapped:）]autorelease]；
}
-（无效）updateBackButton{
如果（[self.webView canGoBack]）{
if（！self.navigationItem.LeftBarButtonim）{
[self.navigationItem setHidesBackButton:是动画：是]；
UIBarButtonItem*backItem=[[[UIBarButtonItem alloc]initWithTitle:@“由于您已获取
webView
的本地实例，因此无法在
ViewDidLoad
的范围之外访问它。要访问
webView
的
实例，您需要像这样获取公共属性

@property(nonatomic, weak) UIWebView *webView

- (void)viewDidLoad{

    [super viewDidLoad];

     //Create UIWebView
            self.webView = [[UIWebView alloc]initWithFrame:self.view.frame];
            self.webView.delegate = self;
            [self.webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"https://dylanduff.github.io/WidgetStore/"]]];
            [self.view addSubview:self.webView];
            self.webView.backgroundColor = [UIColor whiteColor];

            //NSString *theTitle=[self.webView stringByEvaluatingJavaScriptFromString:@"document.title"];
            self.title = @"Widget Store";

        //Create back button
            //self.navigationItem.leftBarButtonItem = [[[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addButtonTapped:)] autorelease];

}

现在需要将webView对象存储在前面声明的公共属性中，以便可以在整个类中使用该属性，viewDidLoad方法如下所示

@property(nonatomic, weak) UIWebView *webView

- (void)viewDidLoad{

    [super viewDidLoad];

     //Create UIWebView
            self.webView = [[UIWebView alloc]initWithFrame:self.view.frame];
            self.webView.delegate = self;
            [self.webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"https://dylanduff.github.io/WidgetStore/"]]];
            [self.view addSubview:self.webView];
            self.webView.backgroundColor = [UIColor whiteColor];

            //NSString *theTitle=[self.webView stringByEvaluatingJavaScriptFromString:@"document.title"];
            self.title = @"Widget Store";

        //Create back button
            //self.navigationItem.leftBarButtonItem = [[[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addButtonTapped:)] autorelease];

}

由于您已经获取了
webView
的本地实例，因此无法在
ViewDidLoad
的范围之外访问它。要在
ViewDidLoad
之外访问
webView
的实例，您需要像这样获取公共属性

@property(nonatomic, weak) UIWebView *webView

- (void)viewDidLoad{

    [super viewDidLoad];

     //Create UIWebView
            self.webView = [[UIWebView alloc]initWithFrame:self.view.frame];
            self.webView.delegate = self;
            [self.webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"https://dylanduff.github.io/WidgetStore/"]]];
            [self.view addSubview:self.webView];
            self.webView.backgroundColor = [UIColor whiteColor];

            //NSString *theTitle=[self.webView stringByEvaluatingJavaScriptFromString:@"document.title"];
            self.title = @"Widget Store";

        //Create back button
            //self.navigationItem.leftBarButtonItem = [[[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addButtonTapped:)] autorelease];

}

现在需要将webView对象存储在前面声明的公共属性中，以便可以在整个类中使用该属性，viewDidLoad方法如下所示

@property(nonatomic, weak) UIWebView *webView

- (void)viewDidLoad{

    [super viewDidLoad];

     //Create UIWebView
            self.webView = [[UIWebView alloc]initWithFrame:self.view.frame];
            self.webView.delegate = self;
            [self.webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"https://dylanduff.github.io/WidgetStore/"]]];
            [self.view addSubview:self.webView];
            self.webView.backgroundColor = [UIColor whiteColor];

            //NSString *theTitle=[self.webView stringByEvaluatingJavaScriptFromString:@"document.title"];
            self.title = @"Widget Store";

        //Create back button
            //self.navigationItem.leftBarButtonItem = [[[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addButtonTapped:)] autorelease];

}

在viewDidload中，您创建了局部webView变量。当然，从另一个方法中看不到该变量

如果定义了属性webView（正如我从代码中建议的那样），请在viewDidLoad方法中使用self.webView而不是UIWebView*webView。
在viewDidLoad中创建本地webView变量。当然，从其他方法中看不到该变量

如果定义了属性webView（正如我从代码中建议的那样），在viewDidLoad方法中使用self.webView，而不是UIWebView*webView。
应用程序可以编译，但后退按钮不可见：/@DylanDuff您从未在viewDidLoad中调用updateBackButton方法，因此不会创建后退按钮。@DylanDuff您也不需要在代码中使用autorelease。这是早期开发人员创建的产物elopers必须自己进行内存管理。应用程序可以编译，但后退按钮不可见：/@DylanDuff您从未在viewDidLoad中调用updateBackButton方法，因此后退按钮从未创建。@DylanDuff您也不需要在代码中使用autorelease。这是ARC之前开发人员必须保留的一个工件自己动手做内存管理。