iPhone上的stringByTrimmingCharactersInSet错误“由于未捕获的异常'NSInvalidArgumentException'而终止应用程序”

Question

我正在从服务器读回JSON数据，并且试图解析包含HTML URL的特定字符串。 数据位于名为current_weatherIconUrl2的NSString中。 Xcode的控制台输出如下：

2010-07-06 17：17：46.628 WhatToDo [13437：20b]当前条件：URL2 ：(“ http://www.worldweatheronline.com/images/wsymbols01_png_64/wsymbol_0001_sunny.png ”）

我想做的是使用“ stringByTrimmingCharactersInSet”来解析'（'，'“'，以及换行符和换行符，但是我却得到了NSInvalidArgumentException：

2010-06-30 00：18：07.357 WhatToDo [7299：20b] *由于未捕获的异常'NSInvalidArgumentException'而终止应用程序，原因：'* -[NSCFArray stringByTrimmingCharactersInSet：]：无法识别的选择器已发送至实例0x3e84970'

这是从服务器返回的数据的摘录（我要提取的信息以粗体显示）：

2010-07-06 17:17:46.627 WhatToDo[13437:20b] Results: {
    data =     {
        "current_condition" =         (
                        {
                cloudcover = 75;
                humidity = 42;
                "observation_time" = "08:47 AM";
                precipMM = "0.0";
                pressure = 1003;
                "temp_C" = 36;
                "temp_F" = 97;
                visibility = 10;
                weatherCode = 113;
                weatherDesc =                 (
                                        {
                        value = Sunny;
                    }
                );
                **weatherIconUrl =                 (
                                        {
                        value = "http://www.worldweatheronline.com/images/wsymbols01_png_64/wsymbol_0001_sunny.png";
                    }
                );**
                winddir16Point = WSW;
                winddirDegree = 250;
                windspeedKmph = 31;
                windspeedMiles = 19;
            }
        );
    };
}

这是将数据解析为NSString变量的代码。

- (void) readWeather {
    NSLog(@"readWeather started");
    NSMutableArray *imageArray = [[NSMutableArray alloc] init];
    NSData *jsonObjectString;
    NSString *completeString = [NSString stringWithFormat:
                            @"http://www.worldweatheronline.com/feed/weather.ashx?key=988ae47cc3062016100606&lat=25.04&lon=121.55&num_of_days=5&format=json", jsonObjectString];                               

    NSLog(@"Weather URL: %@", completeString);

    NSURL *urlForValidation = [NSURL URLWithString:completeString];               
    NSMutableURLRequest *validationRequest = [[NSMutableURLRequest alloc] initWithURL:urlForValidation];                          
    [validationRequest setHTTPMethod:@"POST"];             
    NSData *responseData = [NSURLConnection sendSynchronousRequest:validationRequest returningResponse:nil error:nil];  
    [validationRequest release];

// Store incoming data into a string
NSString *jsonString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];

// Create a dictionary from the JSON string
NSDictionary *results = [jsonString JSONValue];

NSLog(@"Results: %@", results);

NSArray *data = [[results objectForKey:@"data"] objectForKey:@"current_condition"];

NSArray *data2 = [[results objectForKey:@"data"] objectForKey:@"weather"];

NSCharacterSet *skipSet = [NSCharacterSet characterSetWithCharactersInString:@"("];

for (NSArray *current_condition in data)
{
    // Get title of the image
    NSString *temp_C = [current_condition valueForKey:@"temp_C"];
    NSString *current_weatherDesc = [current_condition valueForKey:@"weatherDesc"];
    NSString *current_weatherIconUrl = [current_condition valueForKey:@"weatherIconUrl"];
    NSString *current_weatherIconUrl2= [current_weatherIconUrl valueForKey:@"value"];

    //Commented out because this will create an exception: 
    //NSString *current_weatherIconUrl3 = [current_weatherIconUrl2 stringByTrimmingCharactersInSet:skipSet];
    //NSLog(@"Current Condition: URL2: %@", *(current_weatherIconUrl3);

    //Commented out because this will create an exception: 
    //current_weatherIconUrl3 = [current_weatherIconUrl3 stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
}

有人可以告诉我我做错了什么，还是有比使用stringByTrimmingCharactersInSet更好的方法？

Answer 1

您实际上得到的错误描述了出了什么问题：

2010-06-30 00：18：07.357 WhatToDo [7299：20b] *由于未捕获的异常'NSInvalidArgumentException'而终止应用程序，原因： '*-[NSCFArray stringByTrimmingCharactersInSet：]：无法识别的选择器已发送至实例0x3e84970'

您正在尝试将无法识别的选择器（ stringByTrimmingCharactersInSet:发送到NSCFArray （ NSArray ）的实例。

显然，此选择器仅存在于NSString ，因此将不起作用。

看来[current_weatherIconUrl valueForKey:@"value"]实际上是一个NSArray ，而不是NSString 。

Answer 2

感谢您的帮助DouweM。我能够进行一些修改，现在代码创建了我需要的变量。 见下文...

NSArray *weatherIconUrl2= [weatherIconUrl valueForKey:@"value"];
NSString *weatherIconUrl3 = [[weatherIconUrl2 valueForKey:@"description"] componentsJoinedByString:@""];
[imageArray addObject:[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:weatherIconUrl3]]]];

-托德

Answer 3

您的json响应格式可能不正确。 因此，请在jsonlint上验证您的JSON响应