Question

我无法在html解析过程中使back按钮（导航中的上一页）工作。我要做的是解析一个html并在viewDidAppear上获取一个pdf文件。在此期间，我希望启用back按钮，因为解析可能需要很长时间。因此用户可以决定离开解析过程。

这是我的代码：

-(void)viewDidAppear:(BOOL)animated
{
    [self performSelector:@selector(getPDFUrl) withObject:nil afterDelay:0];
}

-(void) getPDFUrl
{
    NSURL *programURL = [NSURL URLWithString:@"http://www.example.com/somepdf/"];
    NSData *programHtmlData;
    @try
    {
        programHtmlData = [NSData dataWithContentsOfURL:programURL];
    }
    @catch(NSException* ex)
    {}
    // 2
    TFHpple *programHTMLParser = [TFHpple hppleWithHTMLData:programHtmlData];

    NSString *studiosXpathQueryString =
    @"//div[@class='ultra_wrapper']/div[@class='container columns extra_pad boxed_lay centered']/div[@id='prk_ajax_container']/div[@id='centered_block']/div[@id='main_block']/div[@id='content']/div[@id='main']/div[@class='twelve columns sidebarized']/div[@class='prk_no_composer']/p/a";
    NSArray *programNodes = [programHTMLParser searchWithXPathQuery:studiosXpathQueryString];
    NSMutableArray *activities = [[NSMutableArray alloc] init];
    Tutorial *tutorial;

    if (programNodes.count > 0) {

        for (TFHppleElement *element in programNodes)
        {

            @try
            {
                tutorial = [[Tutorial alloc] init];
                tutorial.url = [element objectForKey:@"href"];
            }
            @catch(NSException* ex)
            {

            }
        }

        NSURL *targetURL = [NSURL URLWithString:tutorial.url];
        webView.scalesPageToFit=YES;
        NSURLRequest *request = [NSURLRequest requestWithURL:targetURL];
        [webView loadRequest:request];
    }
    else
    {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"warning"
                                                        message:@"warning!"
                                                       delegate:self
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:nil];
        [alert show];
    }
}

Answer 1

 [self performSelector:@selector(getPDFUrl) withObject:nil afterDelay:0];

将在主线程上执行。 因此阻止您的用户界面。

你应该使用

[self performSelectorInBackground:@selector(getPDFUrl) withObject:nil];

或者您可以使用NSOperationQueue或NSOperation或更简单的NSBlockOperation。

NSBlockOperation *op = [NSBlockOperation blockOperationWithBlock:^{

   NSLog(@"dasds");

}];

[op start];

按下按钮在解析期间不起作用

1 个答案: