我在添加异步任务之前对我的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验证用户名和密码，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。
代码 -
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<NameValuePair> 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 <Void, Void, String> {
@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<NameValuePair>(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();
}
}
}
}
记录猫 -
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<String> 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;
}
}
答案 0 :(得分：1)
将评论转换为答案
通过查看logcat，我们可以看到问题出现在QuestionActivity的第41行。我们知道currentGame是null。
您需要在此之前设置断点，并查看导致其为null的原因。您可能已发现其他变量/对象为null，最终导致NPE。
答案 1 :(得分：0)
背景错误，只需改变：
startActivity(new Intent(this, QuestionnActivity.class));
为：
startActivity(new Intent(LoActivity.this, QuestionnActivity.class));