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您好，当我尝试从我的 jsonString 中获取对象时，我总是收到 NPE。我尝试了很多东西，甚至多次更改了我的 json，但它就是不起作用。 HTTPResponse 工作正常，当我记录“myObject”时，它给出了正确的对象。但是当我试图在其中获取对象时，它给了我一个 NPE。我测试了json，它是有效的。我还尝试检索一个数组而不是一个对象，但它也给出了一个 NPE。谁能告诉我如何解决这个问题。
我做了一个简单的 jsontester Activity 来测试我的 json:
public class JSONTester extends Activity {
private DefaultHttpClient createHttpClient() {
HttpParams my_httpParams = new BasicHttpParams();
HttpConnectionParams.setConnectionTimeout(my_httpParams, 3000);
SchemeRegistry registry = new SchemeRegistry();
registry.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
ThreadSafeClientConnManager multiThreadedConnectionManager = new ThreadSafeClientConnManager(my_httpParams, registry);
DefaultHttpClient httpclient = new DefaultHttpClient(multiThreadedConnectionManager, my_httpParams);
return httpclient;
}
MikeyJSON mJSON;
Button mBtnGo;
TextView mTxt1;
TextView mTxt2;
TextView mTxt3;
TextView mTxt4;
ProgressDialog mProgressDialog;
private String lang;
private int length; // 0 - 6 (length 7 to length 12)
private int wordPos; // 0 - array length
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_jsontester);
mTxt1 = (TextView) findViewById(R.id.txt1);
mTxt1 = (TextView) findViewById(R.id.txt1);
mTxt1 = (TextView) findViewById(R.id.txt1);
mTxt1 = (TextView) findViewById(R.id.txt1);
mBtnGo = (Button) findViewById(R.id.btnGo);
}
public boolean isNumeric(String str) {
for(int i=0;i<str.length();i++) {
if(Character.isDigit(str.charAt(i))) {
return true;
}
}
return false;
}
public void testJSON(View view) {
if(view==mBtnGo) {
mProgressDialog = new ProgressDialog(this);
mProgressDialog.setMessage("loading");
mProgressDialog.show();
new DownloadNewWords().execute();
}
}
private class DownloadNewWords extends AsyncTask<Void, Void, Void> {
int mStatusCode = 0;
String mResultString;
Exception mConnectionException;
@Override
protected Void doInBackground(Void... args) {
String fetchUrl = "http://www.mikeywebs.nl/json/jsonexample.html";
DefaultHttpClient httpclient = createHttpClient();
HttpGet httpget = new HttpGet(fetchUrl);
try {
HttpResponse response = httpclient.execute(httpget);
StatusLine statusLine = response.getStatusLine();
mStatusCode = statusLine.getStatusCode();
if (mStatusCode == 200){
mResultString = EntityUtils.toString(response.getEntity());
}
} catch (ClientProtocolException e) {
e.printStackTrace();
mConnectionException = e;
} catch (IOException e) {
e.printStackTrace();
mConnectionException = e;
}
return null;
}
@Override
protected void onPostExecute(Void arg) {
mProgressDialog.dismiss();
if (mStatusCode == 200){
mJSON = new MikeyJSON(mResultString);
lang = "English"; //Integer.parseInt(langu);
length = 7; //Integer.parseInt(wordl);
wordPos = 0;
String getWord = mJSON.getResult(lang, length, wordPos);
mTxt4.setText(getWord);
}
else {
Toast.makeText(JSONTester.this, "Gegevens konden niet worden opgehaald. Controleer uw internetverbinding en probeer het opnieuw (" +mConnectionException.toString() + ")" , Toast.LENGTH_LONG).show();
mJSON = null;
}
}
}
}
我使用的 jsonclass 是:
public class MikeyJSON {
private JSONObject myObject;
private JSONArray jsonArray;
int i;
public MikeyJSON(String jsonString) {
Log.i("JSON", "jsonString: " + jsonString);
try {
JSONObject myObject = new JSONObject(jsonString);
Log.i("JSON", "myObject_Object: " + myObject.toString());
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public String getResult(String lang, int length, int wordPos) {
String word = "0";
//0 is Nederlands 1 is English
int la = 0;
if(lang.equals("English")) {
la = 1;
}
//make String length
String le = "length" + Integer.toString(length);
Log.i("PARSE", "get_length: " + le);
//the json
try {
jsonArray = myObject.getJSONArray("galgjejson");
Log.i("JSON", "jsonArray: " + jsonArray.toString());
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return word;
}
}
这是 json:
{ "galgjejson" : [
{ "Nederlands" : [
{ "length7" : [
{ "word" : "android" },
{ "word" : "camping" },
{ "word" : "koekjes" }
]
}
]
},
{ "English" : [
{ "length7" : [
{ "word" : "android" },
{ "word" : "camping" },
{ "word" : "koekjes" }
]
}
]
}
]
}
这是日志:
03-18 14:06:23.178: I/JSON(6719): myObject_Object: {"Nederlands":[{"length7":
[{"word":"android"},{"word":"camping"},{"word":"koekjes"}]}]}
03-18 14:06:23.178: I/PARSE(6719): get_length: length7
03-18 14:06:23.178: D/AndroidRuntime(6719): Shutting down VM
03-18 14:06:23.178: W/dalvikvm(6719): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
03-18 14:06:23.207: E/AndroidRuntime(6719): FATAL EXCEPTION: main
03-18 14:06:23.207: E/AndroidRuntime(6719): java.lang.NullPointerException
03-18 14:06:23.207: E/AndroidRuntime(6719): at me.mikey.my.games.galgjex.MikeyJSON.<init>(MikeyJSON.java:38)
03-18 14:06:23.207: E/AndroidRuntime(6719): at me.mikey.my.games.galgjex.JSONTester$DownloadNewWords.onPostExecute(JSONTester.java:128)
03-18 14:06:23.207: E/AndroidRuntime(6719): at me.mikey.my.games.galgjex.JSONTester$DownloadNewWords.onPostExecute(JSONTester.java:1)
03-18 14:06:23.207: E/AndroidRuntime(6719): at android.os.AsyncTask.finish(AsyncTask.java:631)
03-18 14:06:23.207: E/AndroidRuntime(6719): at android.os.AsyncTask.access$600(AsyncTask.java:177)
03-18 14:06:23.207: E/AndroidRuntime(6719): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
03-18 14:06:23.207: E/AndroidRuntime(6719): at android.os.Handler.dispatchMessage(Handler.java:99)
03-18 14:06:23.207: E/AndroidRuntime(6719): at android.os.Looper.loop(Looper.java:137)
03-18 14:06:23.207: E/AndroidRuntime(6719): at android.app.ActivityThread.main(ActivityThread.java:4745)
03-18 14:06:23.207: E/AndroidRuntime(6719): at java.lang.reflect.Method.invokeNative(Native Method)
03-18 14:06:23.207: E/AndroidRuntime(6719): at java.lang.reflect.Method.invoke(Method.java:511)
03-18 14:06:23.207: E/AndroidRuntime(6719): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
03-18 14:06:23.207: E/AndroidRuntime(6719): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-18 14:06:23.207: E/AndroidRuntime(6719): at dalvik.system.NativeStart.main(Native Method)
哦，第 38 行是:
jsonArray = myObject.getJSONArray("galgjejson");