iPhone/iOS isEqualToString总是返回false

Question

我在我的应用程序中有一个简单的isEqualToString测试,由于某种原因,它始终采用if语句的错误路径,即使控制台显示它应该采用真正的路径.

以下是有问题的代码:

- (void)requestFailed:(ASIHTTPRequest *)request
{   
    NSError *error = [request error];

    NSLog(@"Program requestFailed with error '%@' and reason '%@'", [error localizedDescription], [error localizedFailureReason]);

    NSString *errorMessage = [NSString stringWithFormat:@"%@",[error localizedDescription]];
    if ([[error localizedFailureReason] isEqualToString:@"(null)"])
    {
    }
    else
    {
        errorMessage = [errorMessage stringByAppendingFormat:@"\nReason: %@", [error localizedFailureReason]];
    }

    [Utils msgBox:@"Error with Data Download" message:errorMessage];
}

在控制台中:

2011-04-15 14:27:07.341 Program[79087:207] Program requestFailed with error 'The request timed out' and reason '(null)'
2011-04-15 14:27:07.341 Program[79087:207] Displaying a message box with title 'Error with Data Download' and message 'The request timed out
Reason: (null)'

我的Utils类中的msgBox方法将标题和消息输出到控制台,这是第二行的来源.

我一直在看这个问题,答案一定很容易让人不知所措.有什么建议？(我试图修剪[error localizedDescription]的空白区域,但没有用.)我在最新的4.3 iOS SDK上.

Answer 1

字符串不等于"(null)"字符串为nil,打印到控制台时打印为AS(null).

传递nil isStringEqual将始终返回false.

如果需要检查nil,请将字符串与nil进行比较,而不是"(null)".

if (error != nil)
{
    errorMessage = [errorMessage stringByAppendingFormat:@"\nReason: %@", [error localizedFailureReason]];
}