为什么NSData dataWithContentsOfURL有时返回NULL值？ [英] Why NSData dataWithContentsOfURL sometimes return NULL value?

问题描述

我非常感谢您的将NSData字节转换为NSString？文章，特别是for @ christo16。我以前依赖于ASIHttpRequest只是从PHP服务器获取价值。现在只使用这行代码：

  NSString * pageContents = [NSData dataWithContentsOfURL：[NSURL URLWithString：@http： /www.apple.com]] 
  

我可以获得我想要的功能。

但是为什么有时该行会导致pageContents为NULL。我已经改变了这一行：

  NSString * fullUrl = [NSString stringWithFormat：@http://www.apple。 com]; 
 NSURL * url = [[NSURL alloc] initWithString：fullUrl]; 
 NSData * pageContents; 
 NSString * response = NULL; 
 
 while（response == NULL）
 {
 pageContents = [NSData dataWithContentsOfURL：[NSURL URLWithString：fullUrl]]; 
 response = [NSString stringWithUTF8String：[pageContents bytes]]; 
 NSLog（@content =％@，response）; 
} 
  

有更好的方法吗？直到现在，我没有问题。

解决方案

/ div>

如果检索数据时出错，将返回 nil 。

dataWithContentsOfURL：options：error：消息来找出为什么它返回nil。错误将在您传递的 NSError * 指针中返回。

I am gratefully thanks for the article Convert NSData bytes to NSString?, especially for @christo16. I was previously dependent on ASIHttpRequest just to get value from PHP server. Now using by just this line of code :

NSString *pageContents = [NSData dataWithContentsOfURL: [NSURL URLWithString:@"http://www.apple.com"]]

I can get the functionality that I wanted.

But why is sometimes that line cause pageContents to be NULL. I already change that line into this :

NSString *fullUrl = [NSString stringWithFormat:@"http://www.apple.com"];
NSURL *url = [[NSURL alloc] initWithString:fullUrl];
NSData *pageContents;
NSString *response = NULL;

while(response==NULL)
{
    pageContents = [NSData dataWithContentsOfURL: [NSURL URLWithString:fullUrl]];
    response = [NSString stringWithUTF8String:[pageContents bytes]];
    NSLog(@"content = %@", response);
}

Is there any better way of doing this? Up until now, I have no problem. I just wonder whether there is a more elegant way of achieving the same result

Thanks

解决方案

It will return nil if there is an error retrieving the data.

You can use the dataWithContentsOfURL:options:error: message to find out why it's returning nil. The error will be returned in the NSError* pointer that you pass.

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