我正在尝试使用putextra()和getextra()，但我的程序在实现后崩溃了
浏览我的代码，让我知道我的错误
如果我没有使用getextra()和putextra()，则代码可以正常运行
这是我获得价值的第一堂课
public class Assess extends ListActivity {
String itm;
ArrayAdapter<String> Adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
getListView().setBackgroundResource(R.drawable.background);
Adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, getResources()
.getStringArray(R.array.English));
setListAdapter(Adapter);
getListView().setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int pos,
long arg3) {
selectItem(pos);
itm = getListView().getItemAtPosition(pos).toString();
// Toast.makeText(getApplicationContext(), "CLicked",
// Toast.LENGTH_SHORT).show();
}
});
}
public void selectItem(int pos) {
switch (pos) {
case 0: {
Intent i;
List<Question> questions = getQuestionSetFromDb();
// Initialise Game with retrieved question set ///
GamePlay c = new GamePlay();
c.setQuestions(questions);
c.setNumRounds(getNumQuestions());
((ChuckApplication) getApplication()).setCurrentGame(c);
// Start Game Now.. //
i = new Intent(this, QuestionActivity.class);
**i.putExtra("itemname", itm);**
//startActivityForResult(i, Constants.PLAYBUTTON);
startActivity(i);
//this.finish();
break;
}
}
}
现在我正在尝试传递项目名称的第二课
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.question);
topic1 = i.getStringExtra("itemname");
Log.i("sanket", topic1);
/**
* Configure current game and get question
*/
currentGame = ((ChuckApplication) getApplication()).getCurrentGame();
currentQ = currentGame.getNextQuestion();
RadioGroup rdgb = (RadioGroup) findViewById(R.id.group1);
rdgb.setOnCheckedChangeListener(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)));
}
/*
* @Override public void onClick(View arg0) { //Log.d("Questions",
* "Moving to next question");
*//**
* validate a checkbox has been selected
*/
/*
* if (!checkAnswer()) 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); startActivity(i);
* finish(); } }
*/
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (a > 0) {
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() {
String answer = getSelectedAnswer();
if (answer == null) {
// Log.d("Questions", "No Checkbox selection made - returning");
return false;
} else {
// Log.d("Questions",
// "Valid Checkbox selection made - check if correct");
if (currentQ.getAnswer().equalsIgnoreCase(answer)) {
// Log.d("Questions", "Correct Answer!");
currentGame.incrementRightAnswers();
} else {
// Log.d("Questions", "Incorrect Answer!");
currentGame.incrementWrongAnswers();
}
return true;
}
}
/**
*
*/
public String getSelectedAnswer() {
RadioButton c1 = (RadioButton) findViewById(R.id.answer1);
RadioButton c2 = (RadioButton) findViewById(R.id.answer2);
RadioButton c3 = (RadioButton) findViewById(R.id.answer3);
RadioButton c4 = (RadioButton) findViewById(R.id.answer4);
if (c1.isChecked()) {
return c1.getText().toString();
}
if (c2.isChecked()) {
return c2.getText().toString();
}
if (c3.isChecked()) {
return c3.getText().toString();
}
if (c4.isChecked()) {
return c4.getText().toString();
}
return null;
}
@Override
public void onCheckedChanged(RadioGroup group, int checkedId) {
// TODO Auto-generated method stub
// Log.d("Questions", "Moving to next question");
a++;
/**
* validate a checkbox has been selected
*/
if (!checkAnswer())
return;
/**
* check if end of game
*/
if (currentGame.isGameOver()) {
// db.open();
// db.insertOptions(topic1, currentGame.getRight(), month);
// 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();
// db.close();
} else {
Intent i = new Intent(this, QuestionActivity.class);
startActivity(i);
finish();
}
}
}
或者是否有其他方式可以将数据从一个页面传送到putextra()和getextra()以外的其他页面。
这是我的LOGCAT
02-04 10:33:35.697: E/AndroidRuntime(1776): FATAL EXCEPTION: main
02-04 10:33:35.697: E/AndroidRuntime(1776): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.tmm.android.chuck/com.tmm.android.chuck.QuestionActivity}: java.lang.NullPointerException: println needs a message
02-04 10:33:35.697: E/AndroidRuntime(1776): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
02-04 10:33:35.697: E/AndroidRuntime(1776): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
02-04 10:33:35.697: E/AndroidRuntime(1776): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
02-04 10:33:35.697: E/AndroidRuntime(1776): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
02-04 10:33:35.697: E/AndroidRuntime(1776): at android.os.Handler.dispatchMessage(Handler.java:99)
02-04 10:33:35.697: E/AndroidRuntime(1776): at android.os.Looper.loop(Looper.java:130)
02-04 10:33:35.697: E/AndroidRuntime(1776): at android.app.ActivityThread.main(ActivityThread.java:3683)
02-04 10:33:35.697: E/AndroidRuntime(1776): at java.lang.reflect.Method.invokeNative(Native Method)
02-04 10:33:35.697: E/AndroidRuntime(1776): at java.lang.reflect.Method.invoke(Method.java:507)
02-04 10:33:35.697: E/AndroidRuntime(1776): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
02-04 10:33:35.697: E/AndroidRuntime(1776): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
02-04 10:33:35.697: E/AndroidRuntime(1776): at dalvik.system.NativeStart.main(Native Method)
02-04 10:33:35.697: E/AndroidRuntime(1776): Caused by: java.lang.NullPointerException: println needs a message
02-04 10:33:35.697: E/AndroidRuntime(1776): at android.util.Log.println_native(Native Method)
02-04 10:33:35.697: E/AndroidRuntime(1776): at android.util.Log.i(Log.java:158)
02-04 10:33:35.697: E/AndroidRuntime(1776): at com.tmm.android.chuck.QuestionActivity.onCreate(QuestionActivity.java:48)
02-04 10:33:35.697: E/AndroidRuntime(1776): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
02-04 10:33:35.697: E/AndroidRuntime(1776): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
02-04 10:33:35.697: E/AndroidRuntime(1776): ... 11 more
答案 0 :(得分：1)
尝试获取如下字符串：
首先更改onItemClickListener，如下所示：您需要为itm变量指定值，然后调用selectItem()方法，以使itm变量不为空。
getListView().setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int pos,
long arg3) {
itm = getListView().getItemAtPosition(pos).toString();
selectItem(pos);
}
});
在另一项活动中获取字符串，如下所示：
String topic1 =getIntent().getStringExtra("itemname");
答案 1 :(得分：1)
首先在itm的{{1}}实现中初始化OnItemClickListener字符串，然后调用ListView方法。
selectItem()并在收到 getListView().setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int pos,
long arg3) {
itm = getListView().getItemAtPosition(pos).toString(); // initialize it first.
selectItem(pos);
// Toast.makeText(getApplicationContext(), "CLicked",
// Toast.LENGTH_SHORT).show();
}
});
时，将此字符串设为
Activity答案 2 :(得分：0)
您应该从getIntent()读取字符串。阅读如下
topic1 = getIntent().getStringExtra("itemname");
答案 3 :(得分：0)
它必须是NullPointerException，因为“itm”在该范围内始终为null 你为什么不这样做：
itm = getListView().getItemAtPosition(pos).toString();
selectItem(pos,itm);
然后在此方法中将其作为额外传递 希望有所帮助：）