iphone - 应用因WebView而崩溃

Question

在我的应用程序中，我使用UIwebview来显示网站，但是，每当我单击“后退”按钮并开始与应用程序中的其他部分一起播放时，该应用程序大多会无故崩溃。我怀疑Webview导致了此问题，因为仅当我尝试打开W​​ebview时它才崩溃。

我已经使用NSURLConnection加载了webview并创建了webview， View 中的连接对象为nil将消失方法。

@implementation NewsWebSiteViewController

@synthesize connection,rcvdData,spinner1,currentSite,webView,newsWebsite;

- (void)viewDidLoad {
    [super viewDidLoad];
    @try {
        self.webView.delegate=self;
        [UIApplication sharedApplication].networkActivityIndicatorVisible=YES;
        self.title= self.newsWebsite.title;
        self.webView.backgroundColor =[UIColor groupTableViewBackgroundColor];
        self.spinner1 = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
        CGRect center = [self.view bounds];
        CGSize winCenter = center.size;
        CGPoint pont = CGPointMake(winCenter.width/2,winCenter.height/2);
        [spinner1 setCenter:pont];
        [self.view addSubview:spinner1];
        [self.spinner1 startAnimating];
        NSString *url = newsWebsite.link;
        NSURLRequest *theReq =[NSURLRequest requestWithURL:[NSURL URLWithString:url] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:20.0];
        self.connection = [[NSURLConnection alloc] initWithRequest:theReq delegate:self];
        if(self.connection) {
            self.rcvdData = [[NSMutableData data] retain];
        }
        else {
        UIAlertView *alert = [[[UIAlertView alloc] initWithTitle:@"Error!" message:@"We are having a problem connecting to the internet, why not try again or try sometime later!.." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil] autorelease];
        [alert show];
        }
        webView.multipleTouchEnabled=YES;
        webView.scalesPageToFit=YES;
    }
    @catch (NSException * e) {
        }  
}

-(void) goBack {
    self.webView =nil;
    [self.navigationController popViewControllerAnimated:YES];
}

-(void) viewWillDisappear:(BOOL)animated {

    [self.connection cancel];
    self.connection=nil;
    [self.webView stopLoading];
    self.webView=nil;

    [UIApplication sharedApplication].networkActivityIndicatorVisible=NO;

    if (self.spinner1 ==nil) {

    }

    else {
        [self.spinner1 stopAnimating];
    }

}

-(void) webViewDidFinishLoad:(UIWebView *)webView {

    [UIApplication sharedApplication].networkActivityIndicatorVisible=NO;

    if (self.spinner1 ==nil) {

    }
    else {
        [self.spinner1 stopAnimating];
    }
}

-(void) viewDidAppear:(BOOL)animated  {
    [UIApplication sharedApplication].networkActivityIndicatorVisible=NO;

}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}


- (void)viewDidUnload {
    [super viewDidUnload];
}


-(void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    [self.rcvdData setLength:0];
}


-(void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [self.rcvdData appendData:data];
}


-(void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    if (self.spinner1 ==nil) {
        }
    else {
        [self.spinner1 stopAnimating];
        }
    [connection release];
    [rcvdData release];
    UIAlertView *alert = [[[UIAlertView alloc] initWithTitle:@"Error!" message:@"We are having a problem connecting to the internet, why not try again or try sometime later!.." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil] autorelease];
    [alert show];
}


-(void)connectionDidFinishLoading:(NSURLConnection *)connection {
    [connection release];
    [rcvdData release];
    NSString *url = newsWebsite.link;
    NSURL *url1 =  [NSURL URLWithString:url];
    [self.webView loadData:self.rcvdData MIMEType:@"text/html" textEncodingName:@"UTF-8" baseURL:url1];
}

- (void)dealloc {
    [super dealloc];
    [self.spinner1 release];
}

@end

Answer 1

首先，这是C / Objective-C中的相等/不相等的一个小入门:

假设您有一个BOOL值(即可以为YES或NO，“On”或“Off”，“True”或“False”的值)，称为isEnabled。现在，如果我已将此BOOL值(有时称为“标志”)分配为"is"，则可以有条件地测试其值，如下所示:

BOOL isEnabled = YES;

if (isEnabled)
{
   // value set to yes
}

除了上述内容外，我还可以使用否定运算符(感叹号-或称为NOT运算符)来翻转 isEnabled的值，并测试其相反的值:

BOOL isEnabled = YES;

// the following reads as "if is *not* enabled"
if (!isEnabled)
{
   // value set to no
}

现在当然在上面的示例中 isEnabled设置为 YES，因此条件将失败。但是，如果我们考虑以下示例，则为 if的属性，即如果 else if在一系列 if和 else if中的任何位置为“met”(即true)，它将执行其中的所有代码，然后忽略其他任何事情:

BOOL isEnabled = NO;

if (isEnabled)
{
   // any code here will not run, as the above if condition will be false
}
else if (!isEnabled)
{
   // this code will run, since the above condition (!isEnabled) will evaluate to true
}
else if (isEnabled)
{
   // this code could never run, since the previous condition was true and all following else if's are ignored
}
else if (!isEnabled)
{
   // this code could never run, since the previous condition was true and all following else if's are ignored
}

尽管上面有两个冗余的 else if，但这是演示条件代码如何工作的好方法。

因此，在您的 webViewDidFinishLoad:方法中，可以用一个更简单的条件代替它，而不必用空白的if来评估if / else条件:

-(void) webViewDidFinishLoad:(UIWebView *)webView 
{
    [UIApplication sharedApplication].networkActivityIndicatorVisible=NO;

    // or, (self.spinner1 != nil)
    if (!self.spinner1) 
    {
        [self.spinner1 stopAnimating];
    }
}

当您对所有if和else if进行了上述更改后，发布堆栈跟踪，我会看到它还有什么可能。