JSON解析Android中：对于x错误没有价值 [英] JSON parsing in android: No value for x error

问题描述

下面是code我用我的AsyncTask

里面

  DefaultHttpClient的HttpClient =新DefaultHttpClient（）;
HTTPGET请求=新HTTPGET（URL）;
request.setHeader（接受，应用/ JSON）;
request.setHeader（内容类型，应用/ JSON）;HTT presponse响应= httpClient.execute（请求）;HttpEntity responseEntity = response.getEntity（）;的char []缓冲区=新的char [（INT）responseEntity.getContentLength（）];
    InputStream的流= responseEntity.getContent（）;
    InputStreamReader的读者=新的InputStreamReader（流）;
    reader.read（缓冲液）;
    stream.close（）;    结果=新的String（缓冲）;
    返回结果;
 

这会返回一个字符串结果，在我onPostExecute方法我尝试解析输入字符串：

 的JSONObject车=新的JSONObject（新的字符串（结果））;
makeEdit.setText（vehicle.getString（使））;
plateEdit.setText（vehicle.getString（板块））;
modelEdit.setText（vehicle.getString（模特））;
yearEdit.setText（vehicle.getString（年））;
 

一旦它到达makeEdit.setText它抛出一个错误 - 不作任何价值。我还是很新的到Android，所以如果有一些明显的错误，不发送死亡威胁。输入文本是下面的JSON字符串：

  {GetJSONObjectResult：{作：福特，模式：焦点访谈，盘子：XXO123GP，年：2006}}
 

解决方案

对于x错误没有价值使用JSON打交道时的消息是pretty常见。这通常导致被忽视code。

通常情况下，当洞JSON，我试图首先看到的人类可读的结构。对于这一点，我通常使用 JSONViewer 。

在您的情况下，结构是这样的：

您看到制作是另一个名为对象中 GetJSONObjectResult 。因此，为了得到它，你首先必须先得到容器对象：

 的JSONObject车辆=（（JSONObject的）新的JSONObject（结果））getJSONObject（GetJSONObjectResult）;
//更容易阅读
JSONObject的集装箱=新的JSONObject（结果）;
JSONObject的车辆= container.getJSONObject（GetJSONObjectResult）;
 

和最后使用对象来获取制作：

  makeEdit.setText（vehicle.getString（使））;
plateEdit.setText（vehicle.getString（板块））;
modelEdit.setText（vehicle.getString（模特））;
yearEdit.setText（vehicle.getString（年））;
 

Here is the code I'm using inside my AsyncTask

DefaultHttpClient httpClient = new DefaultHttpClient();
HttpGet request = new HttpGet(url);    
request.setHeader("Accept", "application/json");
request.setHeader("Content-type", "application/json");

HttpResponse response = httpClient.execute(request);

HttpEntity responseEntity = response.getEntity();

char[] buffer = new char[(int)responseEntity.getContentLength()];
    InputStream stream = responseEntity.getContent();
    InputStreamReader reader = new InputStreamReader(stream);
    reader.read(buffer);
    stream.close();

    result = new String(buffer);
    return result;

This returns a string result and in my onPostExecute method I try to parse that input string:

JSONObject vehicle = new JSONObject(new String(result));
makeEdit.setText(vehicle.getString("make"));
plateEdit.setText(vehicle.getString("plate"));
modelEdit.setText(vehicle.getString("model"));
yearEdit.setText(vehicle.getString("year"));

As soon as it reaches makeEdit.setText it throws an error - no value for make. I'm still very new to android, so don't send death threats if there was some obvious error. The input text is the following JSON string:

{"GetJSONObjectResult":{"make":"Ford","model":"Focus","plate":"XXO123GP","year":2006}}

解决方案

No value for x error message is pretty common when dealing with JSON. This usually resulted by overlooked code.

usually, when dong JSON, I try to see the human readable structure first. For that, I usually use JSONViewer.

In your case, the structure is something like this:

You see that make is within another object called GetJSONObjectResult. Therefore, to get it, you must first get the container object first:

JSONObject vehicle = ((JSONObject)new JSONObject(result)).getJSONObject("GetJSONObjectResult");
//a more easy to read
JSONObject container = new JSONObject(result);
JSONObject vehicle = container.getJSONObject("GetJSONObjectResult");

and finally use the object to get make:

makeEdit.setText(vehicle.getString("make"));
plateEdit.setText(vehicle.getString("plate"));
modelEdit.setText(vehicle.getString("model"));
yearEdit.setText(vehicle.getString("year"));

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