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 异常。然后我在 AsyncTask 中使用了网络访问，所以无论如何我都看不到这个异常的意义。但现在我得到了 Nullpointer 异常。我已经发布了带有错误 logcat 的代码。我已经 google dint 得到了正确的解决方案。所以请任何人告诉我我哪里出错了。我第一次尝试使用 JSON 发送数据.. 我可以不使用 JSON 将数据发送到服务器.. 但需要使用 JSON 发送..
它在这一行崩溃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..