无法启动活动？
我在添加异步任务之前对代码进行了一些更改我的应用程序正确地使用了来自远程服务器的身份validation用户名和密码，但是当登录成功消息消失时无法启动其他活动。 有人建议我添加异步任务现在我添加了但是当我输入正确的用户名和密码时它会停止工作。 当我输入错误的用户名和密码时，其正常工作显示错误的用户名密码信息 如果有人能够知道会发生什么错误，请帮助我。
码-
public class LoActivity extends Activity { Intent i; Button signin; TextView error; CheckBox check; String name = "", pass = ""; byte[] data; HttpPost httppost; StringBuffer buffer; HttpResponse response; HttpClient httpclient; InputStream inputStream; SharedPreferences app_preferences; List nameValuePairs; EditText editTextId, editTextP; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.login); signin = (Button) findViewById(R.id.signin); editTextId = (EditText) findViewById(R.id.editTextId); editTextP = (EditText) findViewById(R.id.editTextP); app_preferences = PreferenceManager.getDefaultSharedPreferences(this); check = (CheckBox) findViewById(R.id.check); String Str_user = app_preferences.getString("username", "0"); String Str_pass = app_preferences.getString("password", "0"); String Str_check = app_preferences.getString("checked", "no"); if (Str_check.equals("yes")) { editTextId.setText(Str_user); editTextP.setText(Str_pass); check.setChecked(true); } signin.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { name = editTextId.getText().toString(); pass = editTextP.getText().toString(); String Str_check2 = app_preferences.getString("checked", "no"); if (Str_check2.equals("yes")) { SharedPreferences.Editor editor = app_preferences.edit(); editor.putString("username", name); editor.putString("password", pass); editor.commit(); } if (name.equals("") || pass.equals("")) { Toast.makeText(Lo.this, "Blank Field..Please Enter", Toast.LENGTH_SHORT).show(); } else { new LoginTask().execute(); } } }); check.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { // Perform action on clicks, depending on whether it's now // checked SharedPreferences.Editor editor = app_preferences.edit(); if (((CheckBox) v).isChecked()) { editor.putString("checked", "yes"); editor.commit(); } else { editor.putString("checked", "no"); editor.commit(); } } }); } public void Move_to_next() { startActivity(new Intent(this, QuestionnActivity.class)); } @SuppressLint("NewApi") private class LoginTask extends AsyncTask { @SuppressLint("NewApi") @Override protected void onPreExecute() { super.onPreExecute(); // Show progress dialog here } @Override protected String doInBackground(Void... arg0) { try { httpclient = new DefaultHttpClient(); httppost = new HttpPost("http://abc.com/login1.php"); // Add your data nameValuePairs = new ArrayList(2); nameValuePairs.add(new BasicNameValuePair("UserEmail", name.trim())); nameValuePairs.add(new BasicNameValuePair("Password", pass.trim())); httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs)); // Execute HTTP Post Request response = httpclient.execute(httppost); inputStream = response.getEntity().getContent(); data = new byte[256]; buffer = new StringBuffer(); int len = 0; while (-1 != (len = inputStream.read(data))) { buffer.append(new String(data, 0, len)); } inputStream.close(); return buffer.toString(); } catch (Exception e) { e.printStackTrace(); } return ""; } @SuppressLint("NewApi") @Override protected void onPostExecute(String result) { super.onPostExecute(result); // Hide progress dialog here if (buffer.charAt(0) == 'Y') { Toast.makeText(LoActivity.this, "login successfull", Toast.LENGTH_SHORT).show(); Move_to_next(); } else { Toast.makeText(LoActivity.this, "Invalid Username or password", Toast.LENGTH_SHORT).show(); } } } } 原木猫 –
09-24 07:59:32.818: E/AndroidRuntime(17602): FATAL EXCEPTION: main 09-24 07:59:32.818: E/AndroidRuntime(17602): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.abc.cyk/com.abc.cyk.QuestionActivity}: java.lang.NullPointerException 09-24 07:59:32.818: E/AndroidRuntime(17602): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 09-24 07:59:32.818: E/AndroidRuntime(17602): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 09-24 07:59:32.818: E/AndroidRuntime(17602): at android.app.ActivityThread.access$600(ActivityThread.java:141) 09-24 07:59:32.818: E/AndroidRuntime(17602): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 09-24 07:59:32.818: E/AndroidRuntime(17602): at android.os.Handler.dispatchMessage(Handler.java:99) 09-24 07:59:32.818: E/AndroidRuntime(17602): at android.os.Looper.loop(Looper.java:137) 09-24 07:59:32.818: E/AndroidRuntime(17602): at android.app.ActivityThread.main(ActivityThread.java:5041) 09-24 07:59:32.818: E/AndroidRuntime(17602): at java.lang.reflect.Method.invokeNative(Native Method) 09-24 07:59:32.818: E/AndroidRuntime(17602): at java.lang.reflect.Method.invoke(Method.java:511) 09-24 07:59:32.818: E/AndroidRuntime(17602): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 09-24 07:59:32.818: E/AndroidRuntime(17602): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 09-24 07:59:32.818: E/AndroidRuntime(17602): at dalvik.system.NativeStart.main(Native Method) 09-24 07:59:32.818: E/AndroidRuntime(17602): Caused by: java.lang.NullPointerException 09-24 07:59:32.818: E/AndroidRuntime(17602): at com.abc.cyk.QuestionActivity.processScreen(QuestionActivity.java:41) 09-24 07:59:32.818: E/AndroidRuntime(17602): at com.abc.cyk.QuestionActivity.onCreate(QuestionActivity.java:33) 09-24 07:59:32.818: E/AndroidRuntime(17602): at android.app.Activity.performCreate(Activity.java:5104) 09-24 07:59:32.818: E/AndroidRuntime(17602): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 09-24 07:59:32.818: E/AndroidRuntime(17602): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 09-24 07:59:32.818: E/AndroidRuntime(17602): ... 11 more 09-24 07:59:38.557: I/Process(17602): Sending signal. PID: 17602 SIG: 9
QuestionnActivity-
public class QuestionActivity extends Activity implements OnClickListener{ private Question currentQ; private GamePlay currentGame; private CountDownTimer counterTimer; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.question); processScreen(); } /** * Configure current game and get question */ private void processScreen() { currentGame = ((CYKApplication)getApplication()).getCurrentGame(); currentQ = currentGame.getNextQuestion(); Button nextBtn1 = (Button) findViewById(R.id.answer1); nextBtn1.setOnClickListener(this); Button nextBtn2 = (Button) findViewById(R.id.answer2); nextBtn2.setOnClickListener(this); Button nextBtn3 = (Button) findViewById(R.id.answer3); nextBtn3.setOnClickListener(this); Button nextBtn4 = (Button) findViewById(R.id.answer4); nextBtn4.setOnClickListener(this); Button nextBtn5 = (Button) findViewById(R.id.answer5); nextBtn5.setOnClickListener(this); /** * Update the question and answer options.. */ setQuestions(); } /** * Method to set the text for the question and answers from the current games * current question */ private void setQuestions() { //set the question text from current question String question = Utility.capitalise(currentQ.getQuestion()); TextView qText = (TextView) findViewById(R.id.question); qText.setText(question); //set the available options List answers = currentQ.getQuestionOptions(); TextView option1 = (TextView) findViewById(R.id.answer1); option1.setText(Utility.capitalise(answers.get(0))); TextView option2 = (TextView) findViewById(R.id.answer2); option2.setText(Utility.capitalise(answers.get(1))); TextView option3 = (TextView) findViewById(R.id.answer3); option3.setText(Utility.capitalise(answers.get(2))); TextView option4 = (TextView) findViewById(R.id.answer4); option4.setText(Utility.capitalise(answers.get(3))); int score = currentGame.getScore(); String scr = String.valueOf(score); TextView score1 = (TextView) findViewById(R.id.score); score1.setText(scr); counterTimer=new CountDownTimer(15000, 1000) { public void onFinish() { if(currentGame.getRound()==20) System.exit(0); currentGame.decrementScore(); processScreen(); } public void onTick(long millisUntilFinished) { TextView time = (TextView) findViewById(R.id.timers); time.setText( ""+millisUntilFinished/1000); } }; counterTimer.start(); } @Override public void onResume() { super.onResume(); } @Override public void onClick(View arg0) { //Log.d("Questions", "Moving to next question"); if(arg0.getId()==R.id.answer5) { new AlertDialog.Builder(this) .setMessage("Are you sure?") .setCancelable(true) .setPositiveButton("Yes", new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int id) { finish(); } }).setNegativeButton("No", null).show(); } else { if(!checkAnswer(arg0)) return; /** * check if end of game */ if (currentGame.isGameOver()){ //Log.d("Questions", "End of game! lets add up the scores.."); //Log.d("Questions", "Questions Correct: " + currentGame.getRight()); //Log.d("Questions", "Questions Wrong: " + currentGame.getWrong()); Intent i = new Intent(this, EndgameActivity.class); startActivity(i); finish(); } else { Intent i = new Intent(this, QuestionActivity.class); finish(); startActivity(i); } } } @Override public boolean onKeyDown(int keyCode, KeyEvent event) { switch (keyCode) { case KeyEvent.KEYCODE_BACK : return true; } return super.onKeyDown(keyCode, event); } /** * Check if a checkbox has been selected, and if it * has then check if its correct and update gamescore */ private boolean checkAnswer(View v) { final Button b = (Button) v; String answer = b.getText().toString(); counterTimer.cancel(); b.setBackgroundResource(R.drawable.ans); b.setEnabled(false); //Log.d("Questions", "Valid Checkbox selection made - check if correct"); if (currentQ.getAnswer().equalsIgnoreCase(answer)) { b.setBackgroundResource(R.drawable.ansgreen); //Log.d("Questions", "Correct Answer!"); currentGame.incrementScore(); } else{ b.setBackgroundResource(R.drawable.ansred); //Log.d("Questions", "Incorrect Answer!"); currentGame.decrementScore1(); } return true; } }
转换评论以回答
通过查看logcat，我们可以看到问题出现在QuestionActivity第41行。 所以我们知道currentGame是null 。
您需要在此之前设置断点，并查看导致该断点的原因。 您可能已经发现其他变量/对象为null ，最终导致NPE 。
上下文是错误的，只是改变：
startActivity(new Intent(this, QuestionnActivity.class));
至：
startActivity(new Intent(LoActivity.this, QuestionnActivity.class));