Question

我正在尝试使用Android 4.0.3使用JSON对象将数据发送到Gsoap服务器。我的Android应用程序遇到了NetworkOnMainThread Exception。然后我在AsyncTask中使用过网络访问，所以无论如何我都没有看到这个Exception中的重点。但现在我得到了Nullpointer Exception。我发布了错误logcat的代码。我已经谷歌dint得到适当的解决方案。所以请有人说我哪里出错了。我正在尝试第一次使用JSON发送数据....我可以在不使用JSON的情况下将数据发送到服务器..但需要使用JSON发送..

它在此行崩溃 doInBack =（DownloadWebPageTask）doInBack.execute（new String [] {“192.168.1.40”}）;

这是我的代码.. MainAcitivty即AndroidJSONParsingActivity

 public class AndroidJSONParsingActivity extends ListActivity {

// url to make request
// private static String url = "http://192.168.1.40";

// JSON Node names
private static final String TAG_CONTACTS = "contacts";
private static final String TAG_ID = "id";
private static final String TAG_NAME = "name";
private static final String TAG_EMAIL = "email";
private static final String TAG_ADDRESS = "address";
private static final String TAG_GENDER = "gender";
private static final String TAG_PHONE = "phone";
private static final String TAG_PHONE_MOBILE = "mobile";
private static final String TAG_PHONE_HOME = "home";
private static final String TAG_PHONE_OFFICE = "office";

// contacts JSONArray
JSONArray contacts = null;

private AsyncTask<String, Void, String> doInBack;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // Hashmap for ListView
    ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>();

    // Creating JSON Parser instance
    JSONParser jParser = new JSONParser();

    doInBack = (DownloadWebPageTask) doInBack
            .execute(new String[] { "http://192.168.1.40" });
    // getting JSON string from URL
    JSONObject json = jParser.getJSONFromUrl(doInBack);

    try {
        // Getting Array of Contacts
        contacts = json.getJSONArray(TAG_CONTACTS);

        // looping through All Contacts
        for (int i = 0; i < contacts.length(); i++) {
            JSONObject c = contacts.getJSONObject(i);

            // Storing each json item in variable
            String id = c.getString(TAG_ID);
            String name = c.getString(TAG_NAME);
            String email = c.getString(TAG_EMAIL);
            String address = c.getString(TAG_ADDRESS);
            String gender = c.getString(TAG_GENDER);

            // Phone number is agin JSON Object
            JSONObject phone = c.getJSONObject(TAG_PHONE);
            String mobile = phone.getString(TAG_PHONE_MOBILE);
            String home = phone.getString(TAG_PHONE_HOME);
            String office = phone.getString(TAG_PHONE_OFFICE);

            // creating new HashMap
            HashMap<String, String> map = new HashMap<String, String>();

            // adding each child node to HashMap key => value
            map.put(TAG_ID, id);
            map.put(TAG_NAME, name);
            map.put(TAG_EMAIL, email);
            map.put(TAG_PHONE_MOBILE, mobile);

            // adding HashList to ArrayList
            contactList.add(map);
        }
    } catch (JSONException e) {
        e.printStackTrace();
        System.out.println("JsonException--- " + e.getMessage());
    }

    /**
     * Updating parsed JSON data into ListView
     * */
    ListAdapter adapter = new SimpleAdapter(this, contactList,
            R.layout.list_item, new String[] { TAG_NAME, TAG_EMAIL,
                    TAG_PHONE_MOBILE }, new int[] { R.id.name, R.id.email,
                    R.id.mobile });

    setListAdapter(adapter);

    // selecting single ListView item
    ListView lv = getListView();

    // Launching new screen on Selecting Single ListItem
    lv.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            // getting values from selected ListItem
            String name = ((TextView) view.findViewById(R.id.name))
                    .getText().toString();
            String cost = ((TextView) view.findViewById(R.id.email))
                    .getText().toString();
            String description = ((TextView) view.findViewById(R.id.mobile))
                    .getText().toString();

            // Starting new intent
            Intent in = new Intent(getApplicationContext(),
                    SingleMenuItemActivity.class);
            in.putExtra(TAG_NAME, name);
            in.putExtra(TAG_EMAIL, cost);
            in.putExtra(TAG_PHONE_MOBILE, description);
            startActivity(in);

        }
    });

}

private class DownloadWebPageTask extends AsyncTask<String, Void, String> {
    @Override
    protected String doInBackground(String... urls) {
        String response = "";
        for (String url : urls) {
            DefaultHttpClient client = new DefaultHttpClient();
            HttpPost httppost = new HttpPost(url);
            try {
                HttpResponse execute = client.execute(httppost);
                InputStream content = execute.getEntity().getContent();

                BufferedReader buffer = new BufferedReader(
                        new InputStreamReader(content));
                String s = "";
                while ((s = buffer.readLine()) != null) {
                    response += s;
                }

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return response;
    }

    @Override
    protected void onPostExecute(String result) {

    }
}

}

JsonParser.java类

public class JSONParser {

static InputStream is = null;
static JSONObject jObj = null;
static String json = "";

// constructor
public JSONParser() {

}

public JSONObject getJSONFromUrl(String url) {

    // Making HTTP request
    try {
        // defaultHttpClient
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);

        HttpResponse httpResponse = httpClient.execute(httpPost);
        HttpEntity httpEntity = httpResponse.getEntity();
        is = httpEntity.getContent();

    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
    } catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }

    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }

    // return JSON String
    return jObj;

}

public JSONObject getJSONFromUrl(AsyncTask<String, Void, String> doInBack) {
    // TODO Auto-generated method stub
    return null;
}
}

SingleMenuItemActivity.java类

public class SingleMenuItemActivity  extends Activity {

// JSON node keys
private static final String TAG_NAME = "name";
private static final String TAG_EMAIL = "email";
private static final String TAG_PHONE_MOBILE = "mobile";
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.single_list_item);

    // getting intent data
    Intent in = getIntent();

    // Get JSON values from previous intent
    String name = in.getStringExtra(TAG_NAME);
    String cost = in.getStringExtra(TAG_EMAIL);
    String description = in.getStringExtra(TAG_PHONE_MOBILE);

    // Displaying all values on the screen
    TextView lblName = (TextView) findViewById(R.id.name_label);
    TextView lblCost = (TextView) findViewById(R.id.email_label);
    TextView lblDesc = (TextView) findViewById(R.id.mobile_label);

    lblName.setText(name);
    lblCost.setText(cost);
    lblDesc.setText(description);
}
}

我的logcat错误报告

 06-08 17:46:55.459: E/AndroidRuntime(2542): java.lang.RuntimeException: Unable to start activity           ComponentInfo{com.androidhive.jsonparsing/com.androidhive.jsonparsing.AndroidJSONParsingAct ivity}: java.lang.NullPointerException
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at android.app.ActivityThread.access$600(ActivityThread.java:123)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at android.os.Handler.dispatchMessage(Handler.java:99)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at android.os.Looper.loop(Looper.java:137)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at android.app.ActivityThread.main(ActivityThread.java:4424)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at java.lang.reflect.Method.invokeNative(Native Method)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at java.lang.reflect.Method.invoke(Method.java:511)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at dalvik.system.NativeStart.main(Native Method)
 06-08 17:46:55.459: E/AndroidRuntime(2542): Caused by: java.lang.NullPointerException
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at com.androidhive.jsonparsing.AndroidJSONParsingActivity.onCreate(AndroidJSONParsingActivity.java:62)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at android.app.Activity.performCreate(Activity.java:4465)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
 06-08 17:46:55.459: E/AndroidRuntime(2542):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)

非常感谢..

Answer 1

检查JsonObject“c”是否真的包含这些字段。可能你会在下面的一行中得到NullPointerException。

    // Storing each json item in variable
        String id = c.getString(TAG_ID);
        String name = c.getString(TAG_NAME);
        String email = c.getString(TAG_EMAIL);
        String address = c.getString(TAG_ADDRESS);
        String gender = c.getString(TAG_GENDER);

        // Phone number is agin JSON Object
        JSONObject phone = c.getJSONObject(TAG_PHONE);
        String mobile = phone.getString(TAG_PHONE_MOBILE);
        String home = phone.getString(TAG_PHONE_HOME);
        String office = phone.getString(TAG_PHONE_OFFICE);

您可以通过以下代码检查jsonobject是否具有特定名称的映射

if(jsonObject.has(TAG_NAME)) {
    String name = c.getString(TAG_NAME);
}

或者您可以检查json是否具有名称的映射但其值为null

if(!jsonObject.isNull(TAG_NAME)) {
    String name = c.getString(TAG_NAME);
}

此外，如果没有映射或名称

的值为null，则可以获取空字符串

if(jsonObject.optString(TAG_NAME)) {
    String name = c.getString(TAG_NAME);
}

修改你不要创建你的asyncTask对象。在调用execute方法之前创建它。

doInBack = new DownloadWebPageTask(); doInBack.execute(...)

Android：使用JSON-Object＆amp ;;将数据从Android发送到服务器HttpClient的

1 个答案: